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

The ODBII 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.

The severity of ODBII code U1177 is moderate.

Common Causes For: U1176 U1176: “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 U1177 SCP (J1850) Invalid or Missing Data for Primary Id

• 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

Common Troubleshooting Steps

The OBD-II code U1177 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 control module is not receiving valid data from a primary module, which can lead to various performance issues. Here are some common troubleshooting steps to diagnose and resolve the U1177 code:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Addressing other codes may resolve the U1177 issue.
• 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.
• **Repair or Replace: Repair any damaged wires or connectors as necessary.
• 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.
• **Signal Quality: If possible, use an oscilloscope to check the signal quality on the SCP bus. Look for any irregularities in the waveform.
• 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.
• **Reprogramming: In some cases, reprogramming or updating the software of the affected module may resolve communication issues.
• 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.
• 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).
• **Check Fuses: Inspect relevant fuses related to the communication modules and replace any that are blown.
• 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.
• 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.
• 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.