What does it mean?
P1131 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Glow Plug Control Module Internal Fault-Voltage Supply Concern .
Symptoms
- Extended cranking and hard starting in cold weather
- White or blue-grey smoke from the exhaust for the first minute after start
- Rough, uneven running and a knocking sound until the engine warms
- Preheat lamp flashing or staying on after the normal glow period
- Malfunction indicator lamp on and preheating disabled altogether
Likely causes
- Weak or discharged battery, or an undercharging alternator leaving system voltage below the module's working range
- Corroded, loose or undersized main power feed to the glow plug module
- Poor module ground: loose bolt, paint under the eyelet or corroded body stud
- Shorted or heavily worn glow plug drawing excessive current and stressing the module output
- Water intrusion into the module connector or into the module housing itself
- Blown high-current fuse or fusible link in the preheat supply
- Internal failure of the control module after prolonged overload
How to fix it
- Test the battery under load and confirm charging voltage at idle before touching the module
- Measure voltage at the module's main feed with the key on and again during preheat; look for excessive drop
- Clean and retighten the module power feed and ground connections, including the body stud
- Measure the resistance of each glow plug individually and replace any that read shorted or far out of specification
- Check the preheat fuse and fusible link, and inspect the connector for corrosion and water
- Command a preheat cycle with a scan tool and watch current draw per circuit where the data is available
- Replace the glow plug control module only after supply, ground and plug resistance all check good, then verify a cold start