What does it mean?
C1124 is a Chassis (ABS, traction control, steering) fault code. It indicates: Sensor 4 Battery Voltage Low .
Symptoms
- Warning lamp for the affected chassis system
- The sensor value is missing, frozen or pegged at one end of its range
- The related driver assistance function is switched off
- Fault sets during cranking and may clear once the engine is running
- Several modules log supply voltage codes in the same session
- Intermittent warnings in wet weather or after washing the vehicle
Likely causes
- Battery that no longer holds charge, or a charging fault that lets system voltage sag
- Voltage drop across a corroded connector or an oxidised splice in the supply wire
- Damaged or partly broken conductor with only a few strands left carrying current
- Loose or rusty ground point shared by that sensor circuit
- Moisture in the connector creating a leakage path that loads the supply
- Blown or badly seated fuse feeding the circuit
- Faulty supply output in the control module
How to fix it
- Check battery state of charge and charging voltage before anything else
- Back probe the sensor connector and record supply voltage with the key on and while cranking
- Perform a voltage drop test on both the feed and the return of that circuit
- Inspect and clean the connector, then check terminal tension and seal condition
- Check the fuse and its holder, and clean the ground stud for that circuit
- Repair or replace the damaged wire or corroded terminal
- Retest with live data and clear the code once the supply stays in range