What does it mean?
C1125 is a Chassis (ABS, traction control, steering) fault code. It indicates: Brake Fluid Level Sensor Input Circuit Failure .
Symptoms
- Red brake warning lamp on, often together with the ABS lamp
- Warning flickers over bumps or when cornering, when the fluid moves in the reservoir
- Brake pedal travels further than normal if fluid really is low
- Message centre reports low brake fluid even when the reservoir is full
- Fluid visibly below the minimum mark or the reservoir empty on inspection
- Warning stays on permanently after brake work
Likely causes
- Genuinely low brake fluid from worn pads or a leak in the hydraulic system
- Failed float or reed switch inside the reservoir cap assembly
- Corroded or water damaged connector on the reservoir cap
- Broken, chafed or shorted wire between the sensor and the module
- Loss of the ground for the sensor circuit
- Cap not fitted correctly after a fluid top up, leaving the float jammed
- Failed input circuit inside the control module
How to fix it
- Look at the reservoir level and compare it with the minimum and maximum marks
- Inspect the pads, callipers, lines and hoses for wear and leaks, and check the fluid condition
- Unplug the sensor connector and watch the warning change state, which proves the circuit
- Bridge the connector terminals carefully and compare the module reading with the open circuit reading
- Measure continuity of the signal and ground wires from the cap to the module connector
- Repair the damaged wire or corroded connector, or replace the reservoir cap sensor assembly
- Top up with the correct specification fluid, bleed if the system was opened, and clear the code