What Causes the ABS Warning Light to Illuminate in the Volkswagen Touran?

[AaliyahRose]

There are multiple states in which the ABS light can illuminate, with different causes and solutions for each state. The details are as follows: State 1: ABS warning light remains constantly illuminated (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 speed signal. This prevents the ABS control unit from determining the vehicle's speed or calculating the wheel slip rate, thus failing to issue appropriate commands to regulate braking. Solution: Clean the dirt from the wheel speed sensor and adjust the gap between the sensor and the tone 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 re-secure any loose connections. State 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: When multiple electrical components are in use, the battery voltage drops below 10.5V. As engine speed increases, voltage rises, causing the ABS light to turn off. This may also occur due to insufficient power supply voltage to the ABS system, such as poor terminal contact or grounding issues. Solution: Check battery specific gravity; inspect the charging system; verify 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 connection of the ABS hydraulic valve body; loose wiring connections at the ABS hydraulic valve body; ABS control unit failure. Solution: Loosen and re-tighten the hydraulic valve body grounding screw, cleaning the contact surface if necessary; check for enlarged terminal gaps; replace the ABS or ABS/ASR control unit. State 4: ABS warning light illuminates during high-speed driving. Cause: The ABS control unit detects a significant discrepancy between rear and front wheel speed signals during high-speed driving; incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's specified tire and wheel rim sizes, as indicated on the fuel filler cap label. State 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch; internal poor contact in the brake light. Solution: With the engine running, depress the brake pedal and manually push the brake switch lever fully downward, then release the pedal to complete self-positioning; replace the brake light switch if necessary. When the ABS warning light is illuminated, it is advisable to avoid continued driving. An illuminated ABS light indicates a malfunction in the anti-lock braking system. During emergency braking, wheel lock-up may occur, causing loss of vehicle control and skidding, preventing the driver from decelerating or adjusting the vehicle's trajectory, posing significant safety risks.