What does it mean?
C1127 is a Chassis (ABS, traction control, steering) fault code. It indicates: TPMS ECU Battery Voltage High .
Symptoms
- Tyre pressure warning lamp on with no actual pressure problem
- Pressure readings missing or the system reported as unavailable
- Other modules record overvoltage codes at the same time
- Lights unusually bright, sometimes brightening with engine speed
- Battery hot or giving off a smell
- Warning appears shortly after a jump start or battery charging
Likely causes
- Overcharging alternator with a defective voltage regulator
- Jump starting or a charger left on a high output setting
- Poor module ground raising the voltage the module measures
- Battery unable to accept charge because of an internal fault, letting voltage rise
- Loose alternator output connection causing spikes on the supply
- Incorrect battery or an added electrical accessory feeding voltage into the circuit
- Internal fault in the module's voltage monitoring circuit
How to fix it
- Measure charging voltage at the battery at idle and at raised engine speed
- Compare the module's reported supply voltage with a meter reading at the battery
- Inspect and clean the battery terminals, main ground straps and the module ground
- Check the alternator output connection for looseness, heat damage and corrosion
- Test the battery, since an internal fault can allow voltage to climb
- Replace the regulator or alternator if the output stays above specification
- Clear the code once voltage is stable and confirm the tyre pressure system operates normally