Often the main cause of a malfunction in a vehicle's electronic control system is mechanical damage to the CAN bus or failure of control units hanging on the CAN bus.
Below in the article are ways to diagnose the CAN bus for various faults. As an example, a typical CAN bus circuit is shown on a Valtra T "series tractor.
Legend:
- ICL- Instrumental Cluster (Dashboard)
- TC1/TC2- Transmission controller (Transmission control unit 1/2)
- E.C.- Electronic controller (Engine control unit)
- PCU- Pump Control Unit
CAN BUS measurements
120 Ohm termination resistors (Sometimes these resistors are called terminators) inside the EC control unit and a resistor located next to the TC1 unit
If the display (on the side pillar) shows a fault code related to the CAN bus, this indicates a fault in the CAN bus wiring or the control unit.
The system can automatically report which control unit cannot receive information (control unit monitors transmit information to each other).
If the display is flashing or the CAN bus message cannot be transmitted through the bus, a multimeter can be used to locate the faulty CAN bus wiring (or faulty control unit).
The CAN bus has no physical damage
If the resistance between the Hi and Lo wires of the CAN bus (at any point) is approximately 60 ohms, then the CAN bus is not physically damaged.
- The EC and TC1 control units are working properly, since the end-of-line resistors (120 Ohms) are located in the EC unit and next to the TC1 unit.
The TC2 control unit and the ICL instrument panel are also intact as the CAN bus passes through these units.
CAN bus is damaged
If the resistance between the Hi and Lo wires of the CAN bus (at any point) is approximately 120 ohms, then the CAN bus wiring is damaged (one or both wires).
The CAN bus is physically damaged
If the CAN bus is damaged, the location of the damage must be determined.
First, the resistance of the CAN-Lo line is measured, for example between the EC and TC2 control units.
Therefore, measurements must be made between Lo-Lo or Hi-Hi connectors. If the resistance is approximately 0 Ohm, then the wire between the measured points is not damaged.
If the resistance is approximately 240 ohms, then the bus is damaged between the measured points. The picture shows damage to the CAN-Lo wire between the TC1 control unit and the ICL instrument panel.
Short circuit in CAN bus
If the resistance between the CAN-Hi and CAN-Lo wires is approximately 0 ohms, then a short circuit has occurred in the CAN bus.
Disconnect one of the control units and measure the resistance between the contacts of the CAN-Hi and CAN-Lo connectors on the control unit. If the device is working properly, reinstall it.
Then disconnect the next device, take measurements. Continue in this manner until the faulty device is detected. The unit is faulty if the resistance is approximately 0 ohms.
If all blocks are checked and the measurements still indicate a short circuit, the CAN bus wiring is faulty. To find where the wires are damaged, they should be checked visually.
CAN bus voltage measurement
Turn on the power and measure the voltage between the CAN-Hi, CAN-Lo wires and the ground wire.
The voltage should be in the range of 2.4 - 2.7 V.
On-board electronics systems in modern cars and trucks have a huge number of additional devices and actuators. In order for the exchange of information between all devices to be as efficient as possible, the car must have a reliable communication network. In the early 80s of the 20th century, Bosch and developer Intel proposed a new network interface - Controller Area Network, which is popularly called Can-bus.
1 About the operating principle of the CAN-bus network interface
The can-bus in a car is designed to provide connection to any electronic devices that are capable of transmitting and receiving certain information. Thus, data on the technical condition of systems and control signals pass over twisted pair cable in digital format. This scheme made it possible to reduce the negative influence of external electromagnetic fields and significantly increase the speed of data transfer via the protocol (the rules by which control units of various systems are able to exchange information).
In addition, DIY car systems have become easier. Due to the use of such a system as part of the vehicle’s on-board network, a certain number of conductors have been freed up, which are capable of providing communication via various protocols, for example, between the engine control unit and diagnostic equipment, alarm system. It is the presence of the Kan-bus in the car that allows the owner to identify controller malfunctions and errors with his own hands using special diagnostic equipment.
CAN bus–This is a special network through which data is transferred and exchanged between various control nodes. Each node consists of a microprocessor (CPU) and a CAN controller, with the help of which the executable protocol is implemented and interaction with the vehicle network is ensured. The Kan bus has at least two pairs of wires - CAN_L and CAN_H, through which signals are transmitted via transceivers - transceivers capable of amplifying the signal from network control devices. In addition, transceivers perform such functions as:
- adjusting the data transfer rate by increasing or decreasing the current supply;
- current limiting to prevent damage to the sensor or shorting of transmission lines;
- thermal protection.
Today, two types of transceivers are recognized - High Speed and Fault Tolerant. The first type is the most common and complies with the standard (ISO 11898-2), it allows you to transfer data at speeds of up to 1MB per second. The second type of transceivers allows you to create an energy-saving network with a transmission speed of up to 120 Kb/sec, while such transmitters are not sensitive to any damage on the bus itself.
2 Features of the network
It should be understood that data is transmitted over the CAN network in the form of frames. The most important of them are the identifier field (Identifire) and the data system (Data). The most commonly used message type on Kanbus is Data Frame. This type of data transfer consists of a so-called arbitration field and determines priority data transfer in the event that several system nodes simultaneously transmit data to the CAN bus.
Each of the control devices connected to the bus has its own input resistance, and the total load is calculated from the sum of all executable blocks connected to the bus. On average, the input resistance of engine control systems that are connected to the CAN bus is 68-70 Ohms, and the resistance of the information and command system can be up to 3-4 Ohms.
3 CAN interface and system diagnostics
CAN control systems not only have different load resistances, but also different message transmission rates. This fact complicates the processing of similar messages within the on-board network. To simplify diagnostics, modern cars use a gateway interface (resistance converter), which is either designed as a separate control unit or built into the car’s engine ECU.
Such a converter is also designed to input or output certain diagnostic information via the “K”-line wire, which is connected during diagnostics or changing network operating parameters either to the diagnostic connector or directly to the converter.
It is important to note that there are currently no specific standards for Can network connectors. Therefore, each protocol determines its own type of connectors on the CAN bus, depending on the load and other parameters.
Thus, when carrying out diagnostic work with your own hands, a unified OBD1 or OBD2 type connector is used, which can be found on most modern foreign and domestic cars. However, some car models, e.g. Volkswagen Golf 5V, Audi S4, do not have a gateway. In addition, the layout of control units and CAN bus is individual for each make and model of car. In order to diagnose a CAN system with your own hands, you use special equipment, which consists of an oscilloscope, a CAN analyzer and a digital multimeter.
Troubleshooting work begins with removing the mains voltage (removing the negative terminal of the battery). Next, the change in resistance between the bus wires is determined. The most common types of CAN bus malfunction in a car are a short circuit or line break, failure of load resistors and a decrease in the level of message transmission between network elements. In some cases, it is not possible to identify a malfunction without using a Can analyzer.
The CAN bus is an interface used to make vehicle control more simplified. This is ensured through the exchange of data between different systems; the information is transferred in encrypted form.
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Where is the CAN bus located?
The CAN module in a car is a network of sensors and controllers that are designed to combine all control devices into one system.
This automotive technology is used as a socket with which the following control units can be connected:
- “signals” - an automatic engine start module can be connected to the anti-theft system;
- anti-lock braking system "ABS";
- safety mechanisms, in particular airbags and their sensors;
- vehicle powertrain control systems;
- instrument cluster;
- cruise control systems;
- air conditioner and heating unit;
- automatic transmission control systems, etc.
A CAN module is a device whose installation location may differ from the vehicle manufacturer.
If it is unknown where the interface is located, this point is clarified in the service documentation for the car; it is usually installed:
- under the hood of a car;
- inside the vehicle;
- under the control combination.
Specifications
Description of the main properties of the CAN diagnostic and analysis system:
- the overall speed of the technology when transmitting packet data varies around 1 MB/s;
- if information is transmitted between control units, the sending speed will be about 500 kb/s;
- When the device operates in “Comfort” mode, data transmission is carried out at 100 kb/s.
Purpose and functions of the can bus
If you correctly install and connect wires to the interface, you can provide the following options:
- reducing the impact of external interference on the functioning of main and additional mechanisms and components;
- the ability to connect and configure any electronic devices, including security systems;
- a simple principle of connecting and operating additional electronic devices and instruments that are available in the car;
- faster procedure for transferring information to certain equipment and vehicle mechanisms;
- the ability to send and receive digital data simultaneously, as well as analyze information;
- quick setup and connection of the remote engine start option.
Channel “Crossover 159” spoke in more detail about the purpose and general characteristics of the CAN module.
Design and principle of operation
By design, this interface is made in the form of a module in a plastic case or a block for connecting conductors. The digital bus includes several CAN cables. This device is connected to the on-board network via a single conductor.
The bus works on the principle of sending data in encrypted form. Each transmitted message has a special unique identifier. There may be information: “the speed of the car is 50 km/h,” “the coolant temperature is 90 degrees Celsius,” etc. When sending messages, all electronic units receive data that is verified by identifiers. If the information is relevant to a specific module, then it is processed, if not, it is ignored.
Depending on the model, the length of the interface identifier can be 11 or 29 bits.
Each device reads information transmitted to the bus. The lower priority transmitter must release the bus because the dominant level distorts its transmission. If the priority of the transmitted packets is higher, then it is not touched. A device that loses connection while sending messages will automatically restore it after a certain time interval.
The CAN bus can operate in several modes:
- Standalone, background or sleeping. When this mode is turned on, all main units and components are turned off and the engine is not started. The bus is still supplied with voltage from the on-board network. Its value is small, which makes it possible to prevent the battery from discharging.
- Wake up or start the interface. In this mode, the device starts working, this happens when the ignition system is turned on. If the vehicle is equipped with a Start/Stop button, the CAN bus starts working when it is pressed. The voltage stabilization function is turned on, as a result of which power begins to flow to the controllers and sensors.
- Turning on the active mode leads to the beginning of the process of information exchange between actuators and regulators. The voltage in the network increases, since the bus can consume up to 85 mA of current.
- Shutdown or sleep mode. When the car engine is stopped, all units and mechanisms connected via the CAN interface are turned off. The power supply to them stops.
User Valentin Belyaev spoke in detail about the operating principle of the digital interface.
Advantages and disadvantages
If the car is equipped with a digital interface, this provides the following advantages:
- Easy to install an alarm on a vehicle. The presence of a CAN bus in a car allows for a faster and simplified algorithm for connecting the security system.
- High speed of sending information between units and systems, which ensures the speed of nodes.
- Good immunity to interference.
- All digital interfaces have a multi-level control system. Thanks to this, you can prevent errors when sending and receiving information.
- The digital interface, working in active mode, performs speed spread across various channels independently. Thanks to this, all systems operate as quickly as possible.
- CAN bus security. If an attempt is made to gain unauthorized access to the vehicle, the system may block components and assemblies.
- Some systems have limitations on the amount of information transmitted. If the car is relatively new and equipped with different electronic devices, this leads to an increase in the load on the data transmission channel. As a result, response time increases.
- Most information transmitted over a digital interface has a specific purpose. The system allocates a small portion of traffic for useful data.
- There may be a problem of lack of standardization. This often happens when using higher-level protocols.
Varieties and labeling
Based on the type of identifier, such devices are divided into two types:
- CAN2, 0A. This is a marking of interfaces that can operate in an 11-bit information transfer format. This type of device is not able to detect pulse errors from blocks that operate with 29 bits.
- CAN2, 0B. This is a marking for buses operating in 11-bit format. The main feature is the ability to transfer information to control units when a 29-bit identifier is detected.
Depending on the area of application, tires are divided into three classes:
- For a vehicle engine. When connecting a bus, the maximum speed of data transfer and communication between control devices is ensured. Information is sent via an additional channel. The main purpose is to synchronize the operation of the microprocessor module with other systems. For example, anti-lock wheel assembly, transmission, etc.
- Comfort class digital interfaces. This class of buses is designed to interact with any device of this type. The interface is used to work with systems for electronically changing the position of electric mirrors, seat heating, sunroof control, etc.
- Information and command devices. They are characterized by similar speed when sending data. Such buses are usually used for communication between systems that are required to service the vehicle.
The Diyordie channel talked about the purpose of the digital interface, as well as its varieties in a car.
Do-it-yourself alarm connection
To connect the security system to the digital interface, you need to know the installation location of the microprocessor alarm control module. This device is installed under the instrument cluster of the car. The unit can be installed behind a glove box or audio system.
Necessary devices and tools
You must first prepare:
- voltage tester - multimeter;
- electrical tape;
- Phillips head screwdriver.
Step-by-step instruction
Installation is done like this:
- When starting the task, you need to make sure that the anti-theft system is working. If the installation of the system has not been completed, you need to connect all devices to the control unit, and it to the battery.
- A search is made for the main cable that goes to the digital interface. This wire is always thick and usually has an orange sheath.
- The microprocessor module of the anti-theft system must be connected to this conductor. To carry out the task, a digital bus block is used.
- If the security system control unit has not been installed, it must be installed. It should be placed in a hidden place, not exposed to moisture. During installation, the module is securely fixed using plastic ties or self-tapping screws.
- All wire connections must be insulated using heat-shrinkable tubing or electrical tape. After connection, the performed actions are diagnosed. If problems arise, you need to use a multimeter to find the damaged area.
- At the last stage, it is necessary to check and configure all data transmission channels. If there are additional channels, they are also configured.
The “Garage Amateur” channel spoke in detail about the installation and connection of the Starline anti-theft system with a CAN bus.
Working with the terminal
Setting options
If you are using a terminal, there are two options to configure the interface:
- Using a special “Configurator” program for your computer. When starting the utility, go to the “Settings” tab and select the CAN item. In the window that opens, the necessary parameters are indicated.
- Using the "CanRegime" commands. Typically this option is used for remote configuration using SMS messages. Commands that are sent from monitoring software may be used.
More details about the commands that are specified after CanRegime:
- Mode—defines the operating mode. If the number is 0, then the digital interface is disabled, if 1, the standard filter is used. Numbers 2 and 3 indicate that the packets belong to the 29- or 11-bit class.
- BaudRate. The command is intended to determine the speed of the digital interface. It is important that this parameter matches the speed of information transfer in the car.
- TimeOut - Defines the timeout for each message. If the received value is too low, then the digital interface will not be able to catch all transmitted messages.
Operating modes
There are several operating modes of the terminal:
- FMS - in it the car owner can find out the total fuel consumption, revolutions, vehicle mileage, axle load, and temperature of the power unit. It is possible to obtain data on the volume of fuel in the tank. To work in this mode, enter the filter type selection menu of the Configurator program. The type of FMS mode and the speed of the digital interface are indicated, after which the “Apply” button is pressed.
- Listening mode is used to receive messages transmitted via a digital interface. To work with it, you need to go to the CAN bus settings in the program and select one of the operating parameters. This could be interface speed or latency; the type of filter does not matter in this case. After specifying the parameters, the “Listen” button is clicked.
- Custom filters are used to link information obtained by listening to the digital interface. After listening to the data, you need to select the type of filtering technology (for 11 or 29 bits). Data decryption is carried out in accordance with technical documentation.
- OBD2 test mode is used to scan the sending speed of information as well as the ID class. To launch this function, the car owner needs to connect directly to the digital interface or. The mode is enabled by entering the “Settings” menu and selecting the “OBD2 Test” option. As a result, the terminal will begin sending requests with specific identifiers at various interface speeds. In the “Device” tab you can view the extracted and decrypted information.
Setting up monitoring software
After successfully connecting the terminal, you need to diagnose the correctness of sending information. This data is transmitted to the monitoring server.
Displaying information in the monitoring server system
Download free installation and use instructions in PDF format
Download the service manual for installation and operation from the links in the table.
Is it possible to make an analyzer with your own hands?
To perform this task, the car owner must have professional skills in the field of electronics:
- The device is assembled according to the diagram presented in the first photo in the gallery. You must first purchase all the parts necessary for manufacturing. The main component is the STM32F103С8Т6 board, equipped with a controller. You will also need an electrical circuit for the stabilizer and a CAN transceiver. You can use the MCP2551 device or another analogue.
- If you want to make the analyzer more technologically advanced, you can add a Bluetooth module to it. Thanks to this, the car owner can save important information to the smartphone’s memory.
- To program the analyzer, use any suitable software. According to reviews, the best option is Arduino or CANHacker utilities. The second utility has more options and has a function for filtering information.
- To flash the firmware, you will need a USB-TTL converter. This device is required for debugging; if it is missing, you can use ST-Link.
- After downloading the utility to the computer, the main file with the EXE extension is flashed into the block using a programmer. If the procedure is completed successfully, then you need to additionally install a jumper on the Bootloader. The assembled device must be synchronized with the computer using a USB cable.
- The next step is to add firmware to the analyzer. To complete the task you will need the MPHIDFlash utility.
- After successfully updating the program, the cable from the computer is disconnected and the jumper is removed. Drivers are being installed. If the assembly is completed correctly, then when connected to a PC, the analyzer will be detected as a COM port.
Photo gallery
Photos of circuits for making an analyzer yourself are given in this section.
What is the price?
Approximate prices for the purchase of CAN devices are shown in the table.
Video “Working with the CAN bus”
The “CAN-Hacker Automotive Data Bus Solutions” channel showed how to work with a digital interface using the example of a Renault Capture car.
In order to manage systems coherently and harmoniously, to ensure the quality and functionality of data transmission, many automotive companies use a modern system known as a CAN bus. The principle of its organization deserves detailed consideration.
general characteristics
Visually, the CAN bus looks like an asynchronous sequence. Its information is transmitted over two twisted conductors, a radio channel or optical fiber.
Several devices can control the bus simultaneously. Their number is not limited, and the information exchange speed is programmed up to 1 Mbit/s.
The CAN bus in modern cars is regulated by the "CAN Solution version 2.0" specification.
It consists of two sections. Protocol A describes the transfer of information using an 11-bit data transmission system. Part B performs these functions when using the 29-bit version.
CAN has personal clock generator nodes. Each of them sends signals to all systems simultaneously. Receiving devices connected to the bus determine whether the signal is within their jurisdiction. Each system has hardware filtering of messages addressed to it.
Varieties and labeling
One of the most famous today is the CAN bus developed by Robert Bosch. CAN BUS (the system is known by this name) can be sequential, where pulse is given pulse by pulse. It's called Serial bus. If information is transmitted over several wires, then this is a parallel bus.
I - control units;
II - system communications.
Based on the types of CAN bus identifiers, there are two types of markings.
In the case when a node supports an 11-bit information exchange format and does not indicate errors on 29-bit identifier signals, it is marked “CAN2.0A Active, CAN2.0B Passive”.
When such generators use both types of identifiers, the bus is labeled "CAN2.0B Active".
There are nodes that support communications in 11-bit format, but when they see a 29-bit identifier in the system, they display an error message. In modern cars, such CAN buses are not used, because the system must be logical and consistent.
The system operates at two types of signal transmission rates - 125, 250 kbit/s. The former are intended for auxiliary devices (window lifters, lighting), and the latter provide main control (automatic transmission, engine, ABS).
Signal transmission
Physically, the CAN bus conductor of a modern car is made of two components. The first one is black and is called CAN-High. The second conductor, orange-brown, is called CAN-Low. Thanks to the presented communication structure, a lot of conductors have been removed from the car circuit. In the production of vehicles, this allows the weight of the product to be reduced to 50 kg.
The total network load consists of disparate block resistances that are part of a protocol called the CAN bus.
The transmission and reception speeds of each system are also different. Therefore, processing of different types of messages is ensured. According to the description of the CAN bus, this function is performed by a signal converter. It's called the electronic gateway.
This device is located in the design of the control unit, but can be designed as a separate device.
The presented interface is also used to output and input diagnostic signals. For this purpose, a unified OBD block is provided. This is a special connector for system diagnostics.
Types of bus functions
There are different types of device presented.
- CAN bus of the power unit. This is a fast channel that transmits messages at a speed of 500 kbit/s. Its main task is to communicate between control units, for example transmission-engine.
- The Comfort system is a slower channel, transmitting data at a speed of 100 kbit/s. It links all Comfort system devices.
- The bus command program also transmits signals slowly (100 kbit/s). Its main purpose is to provide communication between service systems, such as telephone and navigation.
When studying the question of what a CAN bus is, it may seem that in terms of the number of programs it is similar to an aircraft system. However, in order to ensure quality, safety and comfort when driving, no programs will be superfluous.
Bus interference
All control units are connected to the CAN bus by transceivers. They have message receivers, which are selective amplifiers.
The description of the CAN bus stipulates the arrival of messages along the High and Low conductors to the differential amplifier, where it is processed and sent to the control unit.
The amplifier determines this output signal as the difference in voltage between the High and Low wires. This approach eliminates the influence of external interference.
To understand what a CAN bus is and its structure, you should remember its appearance. These are two conductors twisted together.
Since the interference signal arrives on both wires at once, during processing the Low voltage value is subtracted from the High voltage.
Thanks to this, the CAN bus is considered a reliable system.
Message Types
The protocol provides for the use of four types of commands when exchanging information via the CAN bus.
I - CAN bus;
II - resistance resistor;
III - interface.
In the process of receiving and transmitting information, a certain time is allotted for one operation. If it fails, an error frame is generated. Error Frame also lasts a certain amount of time. The faulty unit is automatically disconnected from the bus when a large number of errors accumulate.
System functionality
To understand what a CAN bus is, you need to understand its functional purpose.
It is designed to transmit real-time frames that contain information about a value (for example, a change in speed) or the occurrence of an event from one transmitter node to program receivers.
The command consists of 3 sections: name, event value, time of observation of the variable.
Key importance is attached to the indicator variable. If the message does not contain time information, then this message is accepted by the system upon receipt.
When a communication system computer requests a parameter status indicator, it is sent in priority order.
Bus Contention Resolution
When signals on the bus arrive at multiple controllers, the system chooses in what order each will be processed. Two or more devices can start working almost simultaneously. To ensure that no conflict arises, monitoring is carried out. The CAN bus of a modern car performs this operation while sending a message.
There is a gradation of messages according to priority and recessive gradation. The information that has the lowest numerical value of the arbitration field will win when a conflict occurs on the bus. The remaining transmitters will try to send their frames later if nothing changes.
In the process of transmitting information, the time specified in it is not lost even if there is a conflict situation in the system.
Physical components
The bus device consists, in addition to the cable, of several elements.
Transceiver chips are often found from Philips, as well as Siliconix, Bosch, Infineon.
To understand what a CAN bus is, you should study its components. The maximum length of the conductor at a speed of 1 Mbit/s reaches 40 m. The CAN bus (also known as CAN-BUS) is equipped with a terminator at the end.
To do this, 120 Ohm resistors are installed at the end of the conductors. This is necessary to eliminate message reflections at the end of the bus and ensure that it receives the appropriate current levels.
The conductor itself, depending on the design, can be shielded or unshielded. The end resistance can deviate from the classic one and range from 108 to 132 Ohms.
iCAN technology
When considering vehicle tires, you should pay attention to the engine blocking program.
For this purpose, data exchange via the CAN bus, iCAN module, has been developed. It connects to the digital bus and is responsible for the corresponding command.
It is small in size and attaches to any tire compartment. When the car starts moving, iCAN sends a command to the corresponding blocks, and the engine stalls. The advantage of this program is the absence of signal interruption. The electronic unit is instructed, after which the message disables the functioning of the corresponding actuators.
This type of blocking is characterized by the highest secrecy and, therefore, reliability. In this case, errors are not recorded in the ECU memory. The CAN bus provides all information about the speed and movement of the vehicle to this module.
Anti-theft protection
The iCAN module is installed in any node where the harnesses are located, where the bus is installed. Due to the minimal dimensions and special algorithm of actions, it is almost impossible to detect blocking using conventional methods when committing a theft.
Externally, this module is disguised as various monitoring sensors, which also makes it impossible to detect. If desired, it is possible to configure the operation of the device to automatically protect car windows and mirrors.
If the vehicle has an automatic engine start, iCAN will not interfere with its operation, since it is triggered when the vehicle starts moving.
Having become familiar with the structure and principles of data exchange with which the CAN bus is endowed, it becomes clear why all modern cars use these technologies when developing vehicle control.
The presented technology is quite complex in its design. However, all the functions included in it will ensure the most efficient, safe and comfortable driving.
Existing developments will help ensure vehicle protection even from theft. Thanks to this, as well as a complex of other functions, the CAN bus is popular and in demand.
Task: Get access to the readings of the car's standard sensors without installing additional ones.
Solution: Reading data from the car.
When it comes to monitoring parameters such as speed vehicle and fuel consumption A reliable and proven solution is to install an auto tracker and a fuel level sensor.
If you need access to information such as engine speed, mileage, coolant temperature and other data from the on-board computer, this task is more like a creative one.
It would seem that what could be more logical: If the car already has all the necessary sensors, then why install new ones? Almost all modern cars (especially when it comes to personal business-class cars and expensive special equipment) are standardly equipped with sensors, the information from which is sent to the on-board computer.
The only question is how to access this information. For a long time this problem remained unsolved. But now there are more and more highly qualified engineers working in the satellite monitoring market, who are still able to find a solution to the problem of correctly obtaining data such as:
- engine speed;
- fuel level in the tank;
- car mileage;
- vehicle engine coolant temperature;
- etc.
The solution we will talk about in this article is reading data from the vehicle's CAN bus.
. What's happened ?
CAN (Controller Area Network) is a popular industrial network standard aimed at combining various actuators and sensors into a single network, widely used in automotive automation. Today, almost all modern cars are equipped with so-called digital wiring - an automotive CAN bus.
. Where did the task of reading data from the CAN bus come from?
The task of reading data from the CAN bus appeared as a consequence of the task of optimizing the costs of operating vehicles.
In accordance with typical customer requests, cars and special equipment are equipped with a satellite GLONASS or GPS monitoring system and a fuel circulation control system (based on submersible or ultrasonic fuel level sensors).
But practice has shown that customers are increasingly interested in more economical ways of obtaining data, as well as those that would not require serious intervention in the design and electrics of the car.
Receiving information from the CAN bus was precisely such a solution. After all, it has a whole series advantages:
1. Saving on additional devices
There is no need to incur significant costs for the purchase and installation of various sensors and devices.
2. Maintaining the car warranty
Detection by the manufacturer of third-party interference in the design or electrics of the car threatens with almost guaranteed removal of the vehicle from the warranty. And this is clearly not in the sphere of interests of car owners.
3. Gaining access to information from standard installed electronic devices and sensors.
Depending on the electronic system, a certain set of functions may be standardly implemented in the car. All these functions, theoretically, we can access via the CAN bus. This could be mileage, fuel level in the gas tank, door opening/closing sensors, temperature outside and inside, engine speed, driving speed, etc.
Skysim technical specialists chose a device to test this solution. It has a built-in FMS decoder and can read information directly from the vehicle's CAN bus.
. What are the advantages and disadvantages of a solution that reads data from the CAN bus?
Advantages:
Ability to work in hard real time.
. Ease of implementation and minimal cost of use.
. High resistance to interference.
. Reliable control of transmission and reception errors.
. Wide range of operating speeds.
. Wide spread of technology, availability of a wide range of products from various suppliers.
Flaws:
The maximum network length is inversely proportional to the transmission speed.
. Large size of service data in the packet (relative to useful data).
. Lack of a single generally accepted standard for a high-level protocol.
The network standard provides ample opportunities for virtually error-free data transfer between nodes, leaving the developer the opportunity to put everything into this standard that can fit there. In this respect, the CAN bus is like a simple electrical wire. You can “push” any information flow there that can withstand the bus bandwidth.
There are known examples of transmitting sound and image via CAN bus. There is a known case of creating an emergency communication system along a highway several tens of kilometers long (Germany). (In the first case, a high transmission speed and a short line length were needed, in the second case - vice versa).
Manufacturers, as a rule, do not advertise exactly how they use payload bytes in the packet. Therefore, the FMS device cannot always decipher the data that the CAN bus “sends out”. In addition, not all car brands have a CAN bus. And not all cars of the same make and model may provide the same information.
Example implementation of the solution:
Not long ago, Skysim and its partner implemented a large project to monitor vehicles. The fleet included various foreign-made trucks. In particular, Scania p340 trucks.
In order to analyze the process of obtaining data from the CAN bus, we, in agreement with the customer, conducted relevant studies on three Scania p340 vehicles: one manufactured in 2008, the second from the beginning of 2009 and the third from the end of 2009.
The results were as follows:
- from the first, data were never received;
- from the second only mileage was obtained;
- from the third, all the data of interest was obtained (fuel level, coolant temperature, engine speed, total consumption, total mileage).
The figure shows a fragment of a message from the Wialon information system, where:
Fuel_level - fuel level in the tank in %;
Temp_aqua - Coolant temperature in degrees Celsius;
Taho - Data from the tachometer (rpm).
The rules for implementing the decision were as follows:
1. The Galileo GLONASS/GPS navigation device was connected to the CAN bus of the trucks.
This auto tracker model was chosen due to the optimal combination of functionality, reliability and cost. In addition, it supports FMS (Fuel Monitoring System), a system that allows you to record and monitor the basic parameters of vehicle use, i.e. Suitable for connection to CAN bus.
The connection diagram to the CAN bus from the side of the Galileo device can be found in the user manual. To connect from the car side, you must first find a twisted pair of wires suitable for the diagnostic connector. The diagnostic connector is always accessible and is located close to the steering column. In a 16-pin connector according to the OBD II standard, this is 6-CAN high, 14-CAN low. Please note that for High wires the voltage is approximately 2.6-2.7V, for Low wires it is usually 0.2V less.
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Another unique solution that was used to retrieve data from the CAN bus was the contactless CAN data reader Crocodile (manufactured by JV Technoton, Minsk). It is perfectly suited to work with Galileo instruments.
Advantages of CAN Crocodile technology:
CAN Crocodile allows you to receive data on vehicle operation from the CAN bus without interfering with the integrity of the tire itself.
Data reading occurs without mechanical and electrical contact with wires.
CAN Crocodile is used to connect GPS/GLONASS monitoring systems to the CAN bus, which receive information about engine operating modes, sensor status, faults, etc.
CAN Crocodile does not violate the insulation of CAN wires and “listens” to the exchange on the bus using a special wireless receiver.
The use of CAN Crocodile is absolutely safe for the car, invisible to the operation of the on-board computer, diagnostic scanner and other electronic systems. The use of CAN Crocodile is especially relevant for vehicles under warranty, in which the connection of any electronic devices to the CAN bus often serves as a reason for voiding the warranty.
2. If the wires are detected and identified correctly, you can start launching the CAN scanner in the Galileo device.
3. FMS standard is selected, speed for most cars is 250,000.
4. Scanning starts.
5. After scanning is completed, you go to the main page of the configurator. If the scan is completed successfully, we have access to the decrypted data.
6. If you don’t see anything other than “end scan”, there are several options. Either the connection was made incorrectly, or the car for some reason does not output data, or the device does not know the code of this CAN bus. As already mentioned, this happens quite often, since there is no single standard for data transmission and processing via CAN. Unfortunately, as practice shows, it is not always possible to obtain complete data from the CAN bus.
But there is one more point that is important to raise.
Most often, the main goal of customers is to control fuel level and consumption.
Even if data from standard sensors is successfully received from the CAN bus, what is their practical value?
The fact is that the main purpose of standard fuel level sensors is to provide an assessment with the degree of accuracy that seems correct to the vehicle manufacturer. This accuracy cannot be matched with the accuracy provided by the submersible fuel level sensor (FLS) manufactured Omnicom or, for example, Technoton.
One of the main tasks that a standard FLS solves is to ensure that the fuel does not suddenly run out, and that the driver understands the general situation with the fuel level in the tank. It is difficult to expect great accuracy from a standard float sensor that is simple in design. In addition, there are cases when a standard sensor distorts the data (for example, when the vehicle is located on a slope).
conclusions
For a number of the above reasons, we recommend not relying entirely on the readings of standard fuel level sensors, but considering each situation individually. As a rule, a suitable solution can only be found together with technical specialists. Different vehicle manufacturers have different accuracy of readings. All customers also have different tasks. And only for a specific task it is advisable to select solutions. For some, a solution that receives data from the CAN bus is quite suitable, since it is several times cheaper and does not require any changes to the vehicle’s fuel system. But for customers with high accuracy requirements, it is reasonable to consider the option of a submersible FLS.
