U1797 SCP Bus Communication Failure
The U1797 code indicates a communication failure on the SCP (Standard Corporate Protocol) data bus, specifically related to a missing acknowledgment from the door lock module. The SCP bus, based on SAE J1850, is a serial communication network used by Ford Motor Company in vehicles from the 1990s and 2000s. When a master module such as the GEM or body control module sends a command to the door locks, the receiving module must send an acknowledgment signal (ACK). The absence of this confirmation means the door lock module is not responding on the bus, which can be due to a faulty module, an open or short in the SCP wiring, or a power/ground issue at the slave module.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty door lock module (integrated actuator or standalone module)
- Open or short circuit in the SCP bus wires (typically SCP+ and SCP-)
- Power or ground failure at the door lock module
- Missing or degraded SCP bus termination resistor
- Corrosion at door module or BCM/GEM connectors
- Faulty master module (GEM, BCM, or body control module) failing to detect a valid response
3. Symptoms You Will Notice
- Door locks inoperative or intermittent operation
- Power door lock switch does not work
- Remote keyless entry (RKE) failure
- Other body functions may be affected (e.g., interior lights, windows)
4. Step-by-Step Diagnosis
Scan for other related codes (e.g., U codes for SCP bus faults)
Inspect SCP bus wiring for opens, shorts, or corrosion at connectors
Check power and ground at the door lock module
Test SCP bus termination resistance (should be around 120 ohms)
Verify door lock module operation by commanding it with a scan tool
If wiring and power are good, suspect a faulty door lock module or master module
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is generally safe to drive, but you may lose power door lock and remote keyless entry functions. The issue is moderate in severity and should be repaired to restore convenience features.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on whether the issue is a wiring repair, connector cleaning, or module replacement. Door lock module replacement can cost $150-$300 plus labor.