WOMS
U code network High severity

U0022 Low Speed CAN Communication Bus (+) Low

The OBD2 code U0022 indicates a problem with the low-speed CAN communication bus, specifically that the positive signal line is reading lower than expected, which can affect communication between modules in the vehicle

Definition

The OBD2 code U0022 indicates a problem with the low-speed CAN communication bus, specifically that the positive signal line is reading lower than expected, which can affect communication between modules in the vehicle

Common causes

  • Faulty CAN bus wiring or connectors
  • Short circuit in the CAN bus
  • Open circuit in the CAN bus
  • Faulty or damaged CAN bus module
  • Poor ground connection
  • Interference from other electrical components
  • Low battery voltage
  • Faulty or incompatible aftermarket accessories
  • Corroded connectors or terminals
  • Software or firmware issues in the control modules

Common misdiagnoses

  • Faulty ABS module
  • Defective engine control module (ECM)
  • Malfunctioning body control module (BCM)
  • Bad wiring or connectors
  • Faulty CAN bus transceiver
  • Defective powertrain control module (PCM)
  • Issues with other communication modules
  • Battery or charging system problems

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide additional context for the issue

  2. 2. Inspect Wiring and Connectors

    Visual Inspection: Check the wiring and connectors associated with the Low Speed CAN bus for any signs of damage, corrosion, or loose connections

  3. 3. Connector Pins

    Ensure that the pins in the connectors are not bent, corroded, or pushed back

  4. 4. Test the CAN Bus Voltage

    Use a multimeter to measure the voltage on the CAN bus wires. The typical voltage levels should be around 2.5V to 3.5V when the bus is idle

  5. 5. Check both the CAN High (CAN H) and CAN Low (CAN L) lines. The voltage difference between these two lines should be approximately 2.0V when the bus is active

  6. 6. Check for Short Circuits

    Inspect the CAN bus wiring for any short circuits to ground or to other wires. A short can cause the voltage to drop, leading to the U0022 code

  7. 7. Test the Modules

    Identify the modules connected to the Low Speed CAN bus. Check if any of these modules are malfunctioning or not communicating properly

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

  9. 9. Check Termination Resistors

    Ensure that the termination resistors (typically 120 ohms) are present and functioning correctly at both ends of the CAN bus. A missing or faulty resistor can cause communication issues

  10. 10. Inspect for Interference

    Look for sources of electrical interference that may be affecting the CAN bus communication. This can include aftermarket accessories or modifications

  11. 11. Scan for Module Updates

    Check if there are any software updates available for the vehicle’s modules. Sometimes, communication issues can be resolved with a software update

  12. 12. Perform a Network Test

    If available, use a professional scan tool to perform a network test to check the integrity of the CAN bus and identify any communication faults

  13. 13. Consult Wiring Diagrams

    Refer to the vehicle’s wiring diagrams to understand the layout of the CAN bus and identify any potential issues in the network.1

  14. 14. Clear Codes and Test Drive

    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.1

  15. 15. Seek Professional Help

    If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who specializes in automotive electronics. By following these troubleshooting steps, you should be able to identify and resolve the issue causing the U0022 code