What Causes the ABS Light to Illuminate in Volkswagen Tiguan?

[DelAnderson]

ABS light illumination can occur in various states, each with different fault causes and solutions, as detailed below: 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 speed and wheel slip rate, thus failing to issue appropriate commands to regulate braking. Solution: Clean the contaminants from the wheel speed sensor and adjust the gap between the sensor and the tone ring to restore normal function. Cause 2: Loose connections in the system wiring or poor contact in the ABS relay can lead to signal issues, causing system malfunction. Solution: Inspect wiring connections and reconnect any loose parts. State 2: ABS warning light intermittently illuminates but turns off when accelerating. Cause: When multiple electrical devices are in use, the battery voltage may drop below 10.5V. As the engine speed increases and voltage rises, the ABS light turns 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 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; loose wiring connections in the ABS hydraulic valve body; or ABS control unit malfunction. Solution: Loosen and retighten the grounding screw on the hydraulic valve body, cleaning the contact surface if necessary. Check for enlarged gaps in connectors. Replace the ABS or ABS/ASR control unit if needed. State 4: ABS warning light illuminates during high-speed driving. Cause: The ABS control unit detects a significant discrepancy between rear and front wheel speeds during high-speed driving. This may also occur due to incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's tire and wheel rim specifications, typically found 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 manually push the brake switch linkage down fully, then release the pedal to complete self-adjustment. Replace the brake light switch if necessary. If the ABS warning light is illuminated, it is advisable not to continue driving. A lit ABS light indicates a malfunction in the anti-lock braking system, which can lead to wheel lock-up during emergency braking, causing loss of vehicle control and skidding. This poses significant safety risks as the driver may be unable to decelerate or adjust the vehicle's trajectory.

[MacJohn]

Last week, the ABS light on my Tiguan also came on. After checking, it turned out to be an issue with the wheel speed sensor. This car has sensors on all four wheels, which are prone to getting muddy or waterlogged, causing signal errors. After the last rain, the left front wheel sensor completely failed and had to be replaced with a new part. It could also be a blown fuse in the ABS control module—I’ve encountered this before, and replacing the fuse fixed it. If you hear unusual noises when braking, check if there’s enough brake fluid. The most troublesome issue is a faulty ABS pump, which can only be confirmed with a computer diagnosis. This problem affects the anti-lock braking function, making it especially dangerous when driving fast in the rain, so it’s best to get it checked immediately. If you can’t fix it yourself, go to a professional shop—don’t take safety lightly.