What does it mean?
C1123 is a Chassis (ABS, traction control, steering) fault code. It indicates: Sensor 3 Battery Voltage Low .
Symptoms
- Warning lamps for the affected system on the dash
- The sensor reads zero, out of range, or is reported as unavailable in live data
- The function that depends on this sensor is disabled
- Fault appears mainly on cold starts or after the vehicle has stood for days
- Other modules record low voltage faults at the same time
- Warning clears itself after a longer drive
Likely causes
- Weak or discharged battery, or a charging system that cannot keep voltage up
- High resistance in the supply wire to that sensor from a corroded terminal or splice
- Poor ground on the sensor circuit or at the module
- Connector partly unlatched or with a pushed back terminal
- Chafed wiring with a partial short that loads the supply
- Failed supply driver inside the module that feeds the sensor
How to fix it
- Test the battery and charging system first, since a flat battery sets several similar codes
- Compare the supply voltage at the sensor connector with the battery voltage
- Perform voltage drop tests along the supply and ground of that sensor circuit
- Inspect the connector for corrosion, spread terminals and moisture
- Check the harness for chafing where it passes brackets and sharp edges
- Repair the corroded terminal, splice or damaged wire
- Replace the sensor or module only if the wiring and supply prove good