WOMS
U code network Medium severity

U1187 SCP (J1850) Invalid or Missing Data for Primary Id

The OBD2 code U1187 SCP (J1850) indicates that there is invalid or missing data for the primary identifier in the vehicle's communication network, which may affect the proper functioning of connected modules

Definition

The OBD2 code U1187 SCP (J1850) indicates that there is invalid or missing data for the primary identifier in the vehicle's communication network, which may affect the proper functioning of connected 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 PCM (Powertrain Control Module)
  • Wiring issues or shorts in the data bus
  • Bad ground connections
  • Faulty sensors or actuators
  • Corrupted software or firmware in the PCM
  • Issues with the vehicle's battery or charging system
  • Problems with the OBDII connector or communication lines
  • Incorrectly configured aftermarket accessories or modules

Troubleshooting steps

  1. 1. Check for Other Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. Addressing other codes may resolve the U1187 code

  2. 2. Inspect Wiring and Connectors

    Visually inspect the wiring and connectors related to the modules on the SCP bus. Look for signs of damage, corrosion, or loose connections

  3. 3. Pay special attention to the ground connections, as poor grounding can lead to communication issues

  4. 4. Check the Modules

    Identify the modules that communicate over the SCP bus. Common modules include the PCM (Powertrain Control Module), BCM (Body Control Module), and others

  5. 5. Ensure that these modules are functioning correctly. If one module is malfunctioning, it can disrupt communication on the bus

  6. 6. Test the SCP Bus

    Use a multimeter or an oscilloscope to test the SCP bus for proper voltage levels and signal integrity

  7. 7. Check for short circuits or open circuits in the wiring harness

  8. 8. Inspect the Battery and Charging System

    Ensure that the vehicle's battery is in good condition and that the charging system is functioning properly. Low voltage can cause communication issues

  9. 9. Perform a Hard Reset

    Disconnect the vehicle's battery for a few minutes to reset the modules. Reconnect the battery and see if the code returns

  10. 10. Update or Reprogram Modules

    If applicable, check for any software updates or reprogramming requirements for the affected modules. Sometimes, manufacturers release updates to fix communication issues

  11. 11. Check for Interference

    Look for any aftermarket devices or modifications that may interfere with the SCP communication, such as alarms, remote starters, or audio systems

  12. 12. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1187 code for your specific vehicle make and model. Manufacturers may have specific fixes or recommendations

  13. 13. Seek Professional Help

    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 issue causing the U1187 code