CAN Bus Troubleshooting Methods?
3 Answers
Here are the troubleshooting methods for the CAN bus: 1. Before inspecting the data bus system, ensure that all electronic control units (ECUs) connected to the data bus are free of functional faults. Functional faults refer to issues that do not directly affect the data bus system but may impact the functional flow of a specific system. For example, a damaged sensor would result in the inability to transmit signals through the data bus. Such functional faults have an indirect impact on the data bus system, affecting communication between ECUs that rely on the sensor's signal. If functional faults are present, they should be addressed first. Record the fault and clear all fault codes from the ECUs. 2. After resolving all functional faults, if data transmission between ECUs remains abnormal, inspect the data bus system. When troubleshooting the data bus system, distinguish between the following two scenarios: (1) Inspection of a two-wire data bus system consisting of two ECUs. (2) Inspection of a two-wire data bus system consisting of three or more ECUs. 3. If no hardware damage is found on the data bus, check whether the fault is caused by a specific ECU. Disconnect all ECUs that communicate via the CAN bus, turn off the ignition, and then reconnect one ECU at a time.
When dealing with CAN bus issues, I always start by reading the fault codes, connecting an OBD scanner to identify communication errors. Then, I inspect the physical connections: locate the CAN wiring harness in the engine compartment and under the dashboard, ensuring there are no damages, corrosion, or loose connectors. Test the resistance by measuring between CAN-H and CAN-L after disconnecting the battery; the standard value is 60 ohms. A reading too high may indicate an open circuit, while too low could suggest a short circuit. Next, measure the voltage with the battery connected: CAN-H should be between 2.5-3.5V, and CAN-L between 1.5-2.5V. If abnormal, use an oscilloscope to check for waveform distortion. Disconnect ECU nodes one by one to locate the fault source, and don't forget to test the ground wires. The vehicle's internal network is intricate, and these small details can prevent a complete system failure.
For CAN bus maintenance, I prefer to start by using diagnostic equipment to check for error codes and confirm if it's a communication failure. Then, I test the terminal resistance: disconnect the bus nodes and measure if the value is 60 ohms. If abnormal, I directly locate the problematic area. Inspect the wiring harness for any mechanical damage or water stains, especially ensuring the connector pins aren't bent. Use a multimeter to measure voltage, ensuring normal fluctuations; for more advanced checks, use a CAN analyzer to monitor data frames in real-time. If there's interference, consider adding shielded wires to prevent electromagnetic noise. Regular maintenance can extend service life—never wait for major issues to take action.
