U1794 – SCP (J1850) Lack of Acknowledgment for Mirrors

The ODBII code U1794 SCP (J1850) indicates a communication issue where the vehicle’s control module is not receiving an acknowledgment signal from the mirrors’ control module, suggesting a potential fault in the wiring, connectors, or the mirrors’ control module itself.

The severity of ODBII code U1794 is moderate.

Common Causes For: U1793 refers to a communication issue between the engine control module (ECM) and the transmission control module (TCM).

• Faulty mirror control module
• Damaged wiring or connectors
• Poor ground connection
• Malfunctioning mirror motors
• Corroded terminals
• Issues with the vehicle’s body control module (BCM)
• Communication network problems (e.g., J1850 bus issues)
• Software glitches or programming errors

Common misdiagnosis for U1794 SCP (J1850) Lack of Acknowledgment for Mirrors

• Faulty mirror control module
• Wiring issues or shorts in the mirror circuit
• Defective mirrors
• Problems with the vehicle’s body control module (BCM)
• Communication issues with the CAN bus
• Low battery voltage or power supply issues
• Faulty connectors or terminals related to the mirror system

Common Troubleshooting Steps

The OBD-II code U1794 indicates a communication issue related to the SCP (Serial Communication Protocol) used in some vehicles, particularly those that utilize the J1850 protocol. This specific code refers to a lack of acknowledgment from the mirrors, which can affect their operation. 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 additional trouble codes. Addressing other related codes may help resolve the U1794 code.
• Inspect Wiring and Connectors: **Visual Inspection: Check the wiring harness and connectors related to the mirrors for any signs of damage, corrosion, or loose connections.
• **Repair or Replace: Repair any damaged wires or connectors, and ensure all connections are secure.
• Test the Mirrors: **Functionality Check: Manually test the mirrors to ensure they are functioning correctly. If they are not responding, they may need to be replaced.
• **Power Supply: Verify that the mirrors are receiving the correct voltage and ground.
• Check the Body Control Module (BCM): The BCM often controls the mirrors. Inspect the BCM for any faults or issues.
• **Reprogram or Replace: If the BCM is faulty, it may need to be reprogrammed or replaced.
• Inspect the SCP Bus: **Bus Integrity: Check the integrity of the SCP bus. Look for shorts, opens, or other issues in the communication lines.
• **Termination Resistors: Ensure that the termination resistors are present and functioning correctly.
• Scan for Communication Issues: Use a scan tool to monitor the communication on the SCP bus. Look for any irregularities or interruptions in communication.
• **Signal Quality: Check the signal quality on the bus lines to ensure they are within specifications.
• Check for Interference: Look for any aftermarket devices or modifications that may be interfering with the SCP communication.
• Perform a Reset: Clear the trouble codes using the OBD-II scanner and see if the code returns after a test drive. Sometimes, a reset can resolve temporary communication issues.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the U1794 code or mirror issues for your specific vehicle make and model. Manufacturers may have specific fixes or updates.
• Professional Diagnosis: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have specialized tools and knowledge to diagnose the problem more effectively. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the U1794 code.