U1174 – SCP (J1850) Invalid or Missing Data for Primary Id

The ODBII code U1174 indicates that there is invalid or missing data for the primary identifier in the SCP (J1850) communication protocol, which may affect the vehicle’s ability to communicate properly with its modules.

The severity of ODBII code U1174 SCP (J1850) Invalid or Missing Data for Primary Id is moderate.

Common Causes For: U1173 U1173: Communication Network Fault Detected

• Faulty wiring or connectors
• Malfunctioning control module
• Corrupted data communication
• Poor ground connections
• Interference from aftermarket devices
• Software issues or bugs in the control module
• Faulty sensors or actuators
• Low battery voltage or power supply issues

Common misdiagnosis for U1174 SCP (J1850) Invalid or Missing Data for Primary Id

• Faulty O2 sensor
• Bad fuel injectors
• Engine misfire
• Transmission issues
• Faulty PCM (Powertrain Control Module)
• Wiring or connector issues
• Bad ground connections
• Faulty CAN bus communication
• Incorrectly configured aftermarket accessories
• Battery or charging system problems

Common Troubleshooting Steps

The OBD-II code U1174 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 U1174 code:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Addressing other codes may resolve the U1174 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 reprogrammed or replaced.
• **Reprogramming: If the module has been replaced, ensure it has been properly programmed to the vehicle.
• 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 issues.
• Battery and Power Supply: **Voltage Check: Verify that the vehicle’s battery is fully charged and that the voltage is within the normal range (typically 12-14 volts).
• **Power Supply: Check the power supply to the affected modules to ensure they are receiving the correct voltage.
• 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 manufacturer-specific TSBs related to the U1174 code or communication issues. There may be known fixes or updates available.
• Professional Diagnosis: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing communication issues. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1174 code.