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

The ODBII 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.

The severity of ODBII code U1187 SCP (J1850) Invalid or Missing Data for Primary Id is moderate.

Common Causes For: U1186 U1186: “Module Communication Failure”

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

• 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

Common Troubleshooting Steps

The OBD-II code U1187 indicates that there is an issue with the communication on the SCP (Serial Communication Protocol) bus, specifically related to the J1850 protocol. This code typically means that the vehicle’s onboard computer is not receiving valid data from a module that it expects to communicate with. Here are some common troubleshooting steps to diagnose and resolve the issue:

• 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.
• 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.
• Pay special attention to the ground connections, as poor grounding can lead to communication issues.
• 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.
• Ensure that these modules are functioning correctly. If one module is malfunctioning, it can disrupt communication on the bus.
• Test the SCP Bus: Use a multimeter or an oscilloscope to test the SCP bus for proper voltage levels and signal integrity.
• Check for short circuits or open circuits in the wiring harness.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.