What Causes the ABS Light to Illuminate in Citroën Vehicles?

[DiBraxton]

ABS light illumination can occur in various states, each with different causes and corresponding solutions, as detailed below: State 1: ABS warning light remains constantly illuminated (most common). Cause 1: The ABS speed sensor's sensing area is covered by mud, sludge, or other contaminants, affecting its ability to detect the corresponding speed signal. This prevents the ABS computer from determining the vehicle's speed and wheel slip rate, thus failing to issue appropriate commands to regulate braking. Solution: Clean the dirt from the speed sensor and adjust the gap between the speed sensor and the signal ring to restore normal function. Cause 2: Poor signal transmission due to loose connections between system wires or poor contact in the ABS relay, leading to system malfunction. Solution: Inspect wire connections and reconnect any loose parts. State 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: When multiple vehicle electrical devices are in use, the battery voltage drops below 10.5V. As engine speed increases, voltage rises, and the ABS light turns off. This may also occur if the ABS system's power supply voltage is too low, such as due to poor terminal contact or grounding issues. Solution: Check the battery's specific gravity; inspect the charging system; examine the power supply (e.g., voltage relay or poor power contact). State 3: ABS warning light remains illuminated after engine start and only turns off when the engine is turned off (IGFF). Cause: Poor grounding contact in the ABS hydraulic valve body; poor contact in the ABS hydraulic valve body wire connector; ABS computer malfunction. Solution: Loosen the grounding screw on the hydraulic valve body, then retighten it, cleaning the contact surface if necessary; check if the connector gap has widened; replace the ABS or ABS/ASR computer. State 4: ABS warning light illuminates during high-speed driving. Cause: During high-speed driving, the ABS computer detects a significant discrepancy between the rear and front wheel speed signals; incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's tire and wheel rim specifications, as indicated on the label near the fuel tank cap. State 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch; poor internal contact in the brake light. Solution: With the engine running, press the brake pedal and use a finger to push the brake switch linkage fully downward, then release the brake pedal to complete self-positioning; replace the brake light switch. If the ABS warning light is illuminated, it is advisable not to continue driving, as this indicates a malfunction in the vehicle's anti-lock braking system. During emergency braking, if the wheels lock up, the vehicle may skid uncontrollably, preventing the driver from slowing down or adjusting the vehicle's trajectory, posing significant safety risks.

[Long]

I've been driving Citroën for over a decade, and the ABS light coming on is quite common. It's usually caused by a dirty or faulty wheel speed sensor, such as when the sensor gets clogged with mud or has an internal short circuit. Another common reason is a malfunctioning ABS pump or control module, and loose wiring connections or blown fuses can also trigger the light. Older Citroën models are particularly prone to this issue because the sensors are positioned close to the tires and easily get dirty. A preliminary check is simple: wipe the sensors around the wheel hubs with a cloth; check if the relevant fuses in the fuse box are blown; if possible, use an OBD scanner to read the fault codes, which can save a lot of time. But don't ignore it—ABS failure can cause skidding during emergency braking, especially in rainy or snowy conditions, which is extremely dangerous. I recommend finding time to visit a reliable repair shop for a diagnosis and not delaying it too long to avoid accidents. I've encountered this issue a few times, and timely repairs have prevented accidents.