U1111: SCP Bus Invalid Data
The U1111 code indicates that a control module has detected invalid or missing data on the SCP (Standard Corporate Protocol) bus, also known as J1850 PWM/VPW. This proprietary Ford network is used in pre-CAN vehicles. The fault means a module isn't receiving the expected Primary Id data from another module, or the data is corrupted or incomplete.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty source control module not transmitting the Primary Id correctly
- Electrical interference or noise on the SCP (J1850) bus
- Abnormal resistance in SCP wiring due to loose connections, corrosion, or physical damage
- Internal failure in the receiving control module
- Incorrect bus termination
- Low system voltage affecting module communication
3. Symptoms You Will Notice
- Check Engine Light or other warning lights on
- Intermittent or complete loss of function in affected systems (e.g., transmission, ABS, instrument cluster)
4. Step-by-Step Diagnosis
Scan all modules for related codes and check for communication faults
Inspect SCP bus wiring for damage, corrosion, or loose connections
Measure bus resistance and voltage at the OBD2 connector (J1850 pins 2 and 10)
Check for proper bus termination (typically 120 ohms across the bus)
Test system voltage and charging system output
Isolate the fault by disconnecting modules one at a time while monitoring bus activity
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, but you may experience drivability issues or loss of some features. Have it diagnosed soon to prevent further problems.
How much does it cost to fix?▼
Diagnosis typically $100-$200. Repairs range from $50 for a wiring fix to $500+ for a module replacement.