WOMS
U code network Medium severity

U1177 SCP (J1850) Invalid or Missing Data for Primary Id

The OBD2 code U1177 indicates that there is invalid or missing data related to the primary identifier in the SCP (J1850) communication protocol, which can affect the vehicle's ability to communicate properly with its...

Definition

The OBD2 code U1177 indicates that there is invalid or missing data related to the primary identifier in the SCP (J1850) communication protocol, which can affect the vehicle's ability to communicate properly with its modules

Common causes

  • Faulty or damaged wiring/connectors
  • Malfunctioning control module
  • Poor ground connections
  • Communication issues between modules
  • Corrupted data or software glitches
  • Faulty sensors or actuators
  • Interference from aftermarket devices
  • Low battery voltage or power supply issues

Common misdiagnoses

  • Faulty O2 sensor
  • Bad fuel injectors
  • Malfunctioning ECM/PCM
  • Wiring issues or shorts
  • Faulty CAN bus communication
  • Defective ABS module
  • Incorrectly installed aftermarket accessories
  • Battery or charging system problems

Troubleshooting steps

  1. 1. Check for Other Codes

    Use an OBD-II scanner to check for any additional trouble codes. Addressing other codes may resolve the U1177 issue

  2. 2. Inspect Wiring and Connectors

    Visual Inspection: Check the wiring and connectors related to the affected modules for any signs of damage, corrosion, or loose connections

  3. 3. Repair or Replace

    Repair any damaged wires or connectors as necessary

  4. 4. Check the SCP Bus

    Bus Integrity: Use a multimeter to check the resistance and continuity of the SCP bus wiring. Ensure that there are no shorts or open circuits

  5. 5. Signal Quality

    If possible, use an oscilloscope to check the signal quality on the SCP bus. Look for any irregularities in the waveform

  6. 6. Inspect Modules

    Module Functionality: Ensure that the primary module (often the PCM or another control module) is functioning correctly. If the module is faulty, it may need to be repaired or replaced

  7. 7. Reprogramming

    In some cases, reprogramming or updating the software of the affected module may resolve communication issues

  8. 8. Check for Ground Issues

    Ensure that all ground connections for the affected modules are secure and free of corrosion. Poor grounding can lead to communication problems

  9. 9. Battery and Power Supply

    Voltage Check: Verify that the vehicle's battery is in good condition and that the voltage is within the normal range (typically 12.4 to 12.6 volts when the engine is off)

  10. 10. Check Fuses

    Inspect relevant fuses related to the communication modules and replace any that are blown

  11. 11. Clear Codes and Test Drive

    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

  12. 12. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1177 code for your specific vehicle make and model. Manufacturers may have specific recommendations or known issues

  13. 13. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have specialized diagnostic tools and experience with your vehicle. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1177 code