SCP Bus Communication Failure - Lost Primary ID
The U1102 code indicates that a control module on the SCP (Standard Corporate Protocol) communication network, based on SAE J1850, has detected invalid data or the absence of the expected Primary ID in a message from another module on the network. This represents a communication failure between controllers, where the periodic information exchanged on the bus is corrupted or fails to reach its destination. This multiplexing protocol was widely used by Ford Motor Company in vehicles before the widespread adoption of CAN. The loss of the Primary ID prevents the receiving module from correctly identifying the source or content of the message, which can lead to limited or inoperative functions in interconnected systems such as the powertrain, instrumentation, or comfort modules.
1. Commonly Affected Makes
2. Most Common Causes
- Internal failure of the sending or receiving control module on the SCP bus
- SCP+ or SCP- bus wiring with short circuit, open circuit, or abnormal resistance
- Network connectors with corroded, bent, or poorly contacting pins
- Incorrect termination or damaged characteristic impedance of the communication bus
- Short to ground or power on the J1850 SCP data lines
- Poor power supply or ground in network modules, causing erratic signal levels
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Intermittent or complete loss of function in interconnected systems (e.g., transmission shifting issues, instrument cluster malfunctions, or climate control problems)
4. Step-by-Step Diagnosis
Scan all modules for related communication codes and verify the U1102 is active.
Inspect the SCP bus wiring and connectors for damage, corrosion, or poor connections.
Measure resistance and voltage on the SCP+ and SCP- lines to check for shorts, opens, or incorrect termination.
Check power and ground supplies to all modules on the network.
If no wiring issues found, isolate the faulty module by disconnecting modules one at a time while monitoring the bus.
5. Frequently Asked Questions
Is it safe to drive?▼
Driving is not recommended as the communication failure can cause unpredictable behavior in critical systems like the transmission or engine control, potentially leading to a breakdown or unsafe driving conditions.
How much does it cost to fix?▼
Repair costs vary widely depending on the root cause. Simple wiring repairs may cost $100-$300, while replacing a faulty module can range from $400 to $1,200 including labor.