U1935: CAN Communication Bus Fault

Definition

The OBD2 code U1935 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a communication issue between modules in the vehicle's network

Common causes

Faulty CAN bus wiring or connectors
Malfunctioning CAN bus modules
Short circuits in the CAN bus
Open circuits in the CAN bus
Interference from other electrical components
Faulty or damaged ECU (Electronic Control Unit)
Poor ground connections
Corroded or damaged terminals
Software issues or bugs in the ECU
Incompatible or faulty aftermarket accessories

Common misdiagnoses

Faulty Engine Control Module (ECM)
Defective Body Control Module (BCM)
Bad wiring or connectors
Malfunctioning CAN bus transceiver
Incorrectly programmed modules
Power supply issues
Faulty sensors or actuators
Software glitches in the vehicle's computer systems

Troubleshooting steps

1. Check for Additional Codes

Use an OBD-II scanner to check for any other trouble codes that may be present. Other codes can provide additional context for the issue
2. Inspect Wiring and Connectors
3. Visually inspect the wiring and connectors associated with the CAN bus. Look for signs of damage, corrosion, or loose connections
4. Pay special attention to the connectors at the ECM (Engine Control Module), BCM (Body Control Module), and any other modules that communicate over the CAN bus
5. Test the CAN Bus Voltage
6. Use a multimeter to check the voltage levels on the CAN High (CAN H) and CAN Low (CAN L) wires. The typical voltage levels should be around 2.5V when idle and should fluctuate between 2.0V and 3.0V when the bus is active
7. If the voltage levels are outside this range, there may be a fault in the wiring or a module
8. Check for Short Circuits
9. Use a multimeter to check for short circuits between the CAN H and CAN L wires and ground or each other. A short circuit can cause communication failures
10. Inspect Modules
11. Check the modules on the CAN bus for proper operation. If one module is malfunctioning, it can disrupt communication for the entire bus
12. If possible, disconnect modules one at a time to see if the code clears or communication is restored
13. Look for Interference
14. Ensure that there are no aftermarket devices or modifications that could be interfering with the CAN bus communication
15. Check for Ground Issues
16. Ensure that all ground connections related to the CAN bus are secure and free of corrosion. Poor grounding can lead to communication issues
17. Perform a Network Test
18. If you have access to a professional-grade scan tool, perform a network test to check the integrity of the CAN bus and identify any faults
19. Clear Codes and Test Drive
20. After performing the above checks and repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns
21. Refer to the vehicle's service manual for specific diagnostic procedures and wiring diagrams related to the CAN bus system. 1
22. Seek Professional Help
23. If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with CAN bus systems. By following these troubleshooting steps, you should be able to identify and resolve the issue causing the U1935 code

Definition

Common causes

Common misdiagnoses

Troubleshooting steps

1. Check for Additional Codes

2. Inspect Wiring and Connectors

3. Visually inspect the wiring and connectors associated with the CAN bus. Look for signs of damage, corrosion, or loose connections

4. Pay special attention to the connectors at the ECM (Engine Control Module), BCM (Body Control Module), and any other modules that communicate over the CAN bus

5. Test the CAN Bus Voltage

6. Use a multimeter to check the voltage levels on the CAN High (CAN H) and CAN Low (CAN L) wires. The typical voltage levels should be around 2.5V when idle and should fluctuate between 2.0V and 3.0V when the bus is active

7. If the voltage levels are outside this range, there may be a fault in the wiring or a module

8. Check for Short Circuits

9. Use a multimeter to check for short circuits between the CAN H and CAN L wires and ground or each other. A short circuit can cause communication failures

10. Inspect Modules

11. Check the modules on the CAN bus for proper operation. If one module is malfunctioning, it can disrupt communication for the entire bus

12. If possible, disconnect modules one at a time to see if the code clears or communication is restored

13. Look for Interference

14. Ensure that there are no aftermarket devices or modifications that could be interfering with the CAN bus communication

15. Check for Ground Issues

16. Ensure that all ground connections related to the CAN bus are secure and free of corrosion. Poor grounding can lead to communication issues

17. Perform a Network Test

18. If you have access to a professional-grade scan tool, perform a network test to check the integrity of the CAN bus and identify any faults

19. Clear Codes and Test Drive

20. After performing the above checks and repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns

21. Refer to the vehicle's service manual for specific diagnostic procedures and wiring diagrams related to the CAN bus system. 1

22. Seek Professional Help

23. If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with CAN bus systems. By following these troubleshooting steps, you should be able to identify and resolve the issue causing the U1935 code