SCP Bus Communication Fault U1186
Diagnostic trouble code U1186 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 Ford-proprietary network operates at 41.6 kbps using pulse width modulation. The fault occurs when a transmitting module fails to send the expected message, data is corrupted, or there is a communication interruption between modules on the SCP bus.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty PCM not transmitting correct data on the SCP bus
- Defective instrument cluster with intermittent SCP communication
- Short or open circuit in SCP+ or SCP- bus wires
- Incorrect or damaged bus termination resistor (typically 120 ohms)
- TCM with communication failure
- Electrical interference or noise on the data bus
- Corroded or damaged network connector pins
- Faulty GEM or convenience module
3. Symptoms You Will Notice
- Check Engine Light or other warning lights illuminated
- Erratic gauge readings or non-functional gauges
- Transmission shifting issues
- Engine performance problems
- Intermittent electrical component operation
4. Step-by-Step Diagnosis
Scan all modules for related communication codes
Inspect SCP bus wiring for shorts, opens, or corrosion
Check bus termination resistance (should be ~60 ohms across SCP+ and SCP- with modules connected)
Perform a network test to identify non-communicating modules
Isolate and test suspect modules (PCM, cluster, TCM, GEM) individually
5. Frequently Asked Questions
Is it safe to drive?▼
The vehicle may still be drivable, but symptoms like erratic gauges or transmission issues can affect safety. It's best to diagnose and repair promptly to avoid further damage.
How much does it cost to fix?▼
Repair costs vary widely depending on the root cause. Simple wiring repairs may cost $100-$300, while module replacement can range from $400 to $1,200 including labor.