U1203 Power Window Bus Communication Fault
The U1203 code indicates that a control module (typically the GEM, BCM, or window module) has detected invalid or missing data on the SCP (J1850) bus related to the power window system. This protocol is used by Ford vehicles from approximately 1996 to 2010. The fault occurs when the expected window data messages are not received, are corrupted, out of range, or do not conform to the SAE J1850 specification.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty driver or passenger power window control module
- Open or short circuit in the SCP bus wiring (SCP+ and SCP- circuits)
- Damaged or out-of-spec SCP bus termination resistor (typically 120 ohms)
- Loose or corroded connections at data bus connectors
- Electromagnetic interference affecting signal integrity on the SCP bus
3. Symptoms You Will Notice
- Power windows may be inoperative or work intermittently
- Other body functions (e.g., locks, mirrors) may also be affected
- Check Engine Light or other warning lights may illuminate
4. Step-by-Step Diagnosis
Scan for all stored codes and note freeze frame data
Inspect SCP bus wiring for damage, shorts, or corrosion
Measure resistance between SCP+ and SCP- at the data link connector; should be approximately 60 ohms (two 120-ohm resistors in parallel)
Check for proper voltage and ground at the window control modules
Test the termination resistors and replace if out of spec
If wiring and resistors are good, suspect a faulty module (GEM, BCM, or window module) and perform module-specific tests
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is generally safe to drive, but power windows and possibly other body functions may not work properly. Have it diagnosed soon to prevent further issues.
How much does it cost to fix?▼
The cost can range from $100 for a simple wiring repair to $500 or more if a module needs replacement, including parts and labor.