U1103 SCP Bus Communication Fault
The U1103 code indicates that a control module has detected a communication failure or missing data on the SCP (Standard Corporate Protocol) bus, which is Ford's proprietary network based on SAE J1850. This protocol operates at 41.6 kbps using pulse-width modulation (PWM) on a single wire. The fault means a module on the network is not properly transmitting or receiving the required primary identification message, which can disrupt coordination between modules such as the PCM, ABS, instrument cluster, or comfort modules.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty module that transmits the Primary ID message
- Open or short circuit in the SCP bus wiring (circuits 914 or 915 on Ford vehicles)
- SCP bus termination resistance out of specification (typically 120 ohms)
- Corrupted or damaged control module software
- Electromagnetic interference on the bus wiring
- Corroded or loose connectors at SCP junction points
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Erratic behavior or failure of multiple systems (e.g., transmission, ABS, gauges)
4. Step-by-Step Diagnosis
Scan all modules for related communication codes and verify the Primary ID message is present on the SCP bus using a scope or scan tool.
Inspect the SCP bus wiring (circuits 914/915) for opens, shorts, or damage; check termination resistance at the OBD2 connector (should be ~60 ohms with two 120-ohm terminators).
Check for loose or corroded connectors at modules and junction points; clean and secure as needed.
If wiring and connectors are good, isolate the faulty module by disconnecting modules one at a time while monitoring the bus signal.
5. Frequently Asked Questions
Is it safe to drive?▼
The vehicle may still be drivable, but you may experience performance issues or loss of certain functions. It is recommended to diagnose and repair the fault promptly to avoid further problems.
How much does it cost to fix?▼
Repair costs vary widely depending on the cause. Simple wiring repairs may cost $100-$200, while replacing a faulty module can range from $300 to $800 or more, including labor.