What Causes the ABS Light to Illuminate in a Mercedes-Benz?

[HaileyFitz]

There are multiple states in which the ABS light may illuminate, with different causes and solutions for each state, as detailed below: State 1: ABS warning light remains constantly lit (most common). Cause 1: The ABS wheel speed sensor's sensing area is covered by dirt, mud, or other contaminants, affecting its ability to detect the corresponding wheel speed signal. This prevents the ABS control module from determining the vehicle's speed and wheel slip rate, thereby disabling its ability to issue commands to regulate braking. Solution: Clean the dirt from the wheel speed sensor and adjust the gap between the sensor and the signal ring to restore normal function. Cause 2: Poor signal transmission due to loose system wiring connections or faulty ABS relay contacts, leading to system malfunction. Solution: Inspect wiring connections and reconnect any loose parts. State 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: When multiple electrical components are in use, the battery voltage may drop below 10.5V. As engine speed increases, the voltage rises, causing the ABS light to turn off. This can also occur if the ABS system's power supply voltage is too low due to poor terminal contact or grounding issues. Solution: Check the battery's specific gravity, inspect the charging system, and verify the power supply (e.g., voltage relay or poor power contact). State 3: ABS warning light remains lit after engine startup and only turns off when the engine is turned off (IGFF). Cause: Poor grounding connection of the ABS hydraulic valve body; faulty wiring connection of the ABS hydraulic valve body; ABS control module malfunction. Solution: Loosen and retighten the grounding screw of the hydraulic valve body, cleaning the contact surface if necessary; check for enlarged terminal gaps; replace the ABS or ABS/ASR control module. State 4: ABS warning light illuminates during high-speed driving. Cause: The ABS control module detects a significant discrepancy between the rear and front wheel speed signals during high-speed driving; 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 all the way down, then release the pedal to complete self-positioning; replace the brake light switch if necessary. If the ABS warning light is illuminated, it is advisable not to continue driving. An illuminated ABS light 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.