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U1635CAN Communication Bus Fault

The OBD2 code U1635 indicates a fault in the CAN (Controller Area Network) communication bus, suggesting a communication issue between modules in the vehicle's network

Definition

The OBD2 code U1635 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
  • Poor ground connections
  • Faulty or damaged sensors on the CAN network
  • Software or firmware issues in the control modules

Common misdiagnoses

  • Faulty Engine Control Module (ECM)
  • Faulty Body Control Module (BCM)
  • Defective wiring or connectors
  • Faulty sensors
  • Battery or charging system issues
  • Faulty transmission control module (TCM)
  • Incorrectly programmed modules
  • Grounding issues

Troubleshooting steps

  1. 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 problem

  2. 2.Inspect the Wiring and Connectors

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

  4. 4.Pay special attention to the connectors on the modules that are part of the CAN network

  5. 5.Check the CAN Bus Termination Resistors

  6. 6.Ensure that the CAN bus has the correct termination resistors (typically 120 ohms) at both ends of the bus. A missing or faulty resistor can cause communication issues

  7. 7.Test the CAN Bus Voltage

  8. 8.Use a multimeter to measure the voltage levels on the CAN High and CAN Low wires. The typical voltage levels should be around 2.5V when idle and should vary when data is being transmitted

  9. 9.If the voltage levels are outside the expected range, there may be a fault in the bus

  10. 10.Inspect Modules on the CAN Bus

  11. 11.Identify all the modules connected to the CAN bus and check for any that may be malfunctioning. A faulty module can disrupt communication

  12. 12.Disconnect each module one at a time and check if the code clears or if communication is restored

  13. 13.Check for Short Circuits or Open Circuits

  14. 14.Use a multimeter to check for shorts or opens in the CAN bus wiring. This includes checking for continuity between the CAN High and CAN Low wires and ground

  15. 15.Scan for Module Communication

  16. 16.Use a scan tool to check if you can communicate with all the modules on the CAN bus. If some modules are unresponsive, it may indicate a problem with those specific modules or their connections

  17. 17.Inspect Ground Connections

  18. 18.Ensure that all ground connections for the modules on the CAN bus are secure and free of corrosion. Poor ground connections can lead to communication issues

  19. 19.Check for Interference

  20. 20.Look for any sources of electrical interference that may be affecting the CAN bus communication, such as aftermarket accessories or modifications

  21. 21.Update or Reprogram Modules

  22. 22.In some cases, a software update or reprogramming of the affected modules may be necessary to resolve communication issues. 1

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

  24. 24.Professional Diagnosis

  25. 25.If the issue persists after performing these steps, consider seeking help from a professional mechanic or automotive technician who has experience with CAN bus systems. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1635 code