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U code network Medium severity

U0166 Lost Communication With Auxiliary Heater Control Module

The OBD2 code U0166 indicates that there is a loss of communication between the vehicle's main control module and the auxiliary heater control module, which may affect the operation of the auxiliary heating system

Definition

The OBD2 code U0166 indicates that there is a loss of communication between the vehicle's main control module and the auxiliary heater control module, which may affect the operation of the auxiliary heating system

Common causes

  • Faulty auxiliary heater control module
  • Damaged wiring or connectors
  • Poor ground connection
  • Blown fuse
  • Corroded terminals
  • Communication network issues (e.g., CAN bus problems)
  • Software or firmware issues in the control module
  • Intermittent electrical connections

Common misdiagnoses

  • Faulty wiring or connectors
  • Malfunctioning main engine control module (ECM)
  • Defective auxiliary heater control module
  • Battery or power supply issues
  • Faulty sensors related to the heating system
  • Software or firmware issues in the vehicle's control modules
  • Issues with the vehicle's communication network (CAN bus)

Troubleshooting steps

  1. 1. Check for Other Codes

    Use an OBD-II scanner to check for any additional trouble codes. Sometimes, other codes can provide context or indicate related issues

  2. 2. Inspect the Wiring and Connectors

    Visual Inspection: Check the wiring harness and connectors associated with the auxiliary heater control module 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 Auxiliary Heater Control Module

    If accessible, test the auxiliary heater control module for proper operation. This may involve checking for power and ground at the module

  5. 5. Use a multimeter to measure voltage and ground at the module's connector

  6. 6. Check for Power and Ground

    Verify that the auxiliary heater control module is receiving the correct voltage and ground. Refer to the vehicle’s wiring diagram for specifications

  7. 7. If there is no power or ground, trace the wiring back to the source to identify any breaks or shorts

  8. 8. Inspect the CAN Bus Communication

    Since U0166 is a communication-related code, check the CAN (Controller Area Network) bus for issues

  9. 9. Look for any other modules that may be having communication problems, as a fault in one module can affect others

  10. 10. Perform a Network Test

    If you have access to a professional scan tool, perform a network test to see if the auxiliary heater control module is communicating with other modules

  11. 11. Check for any communication errors or faults in the network

  12. 12. Check for Software Updates

    Sometimes, software updates for the vehicle’s control modules can resolve communication issues. Check with the manufacturer or a dealership for any available updates

  13. 13. Reset the Codes

    After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  14. 14. Consult Technical Service Bulletins (TSBs)

    Look for any TSBs related to the auxiliary heater control module or communication issues for your specific vehicle make and model

  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 has experience with your vehicle’s specific systems. By following these troubleshooting steps, you should be able to identify the cause of the U0166 code and take appropriate action to resolve the issue