What causes the ABS light to come on in a Golf?

[LeSawyer]

There are several conditions under which the ABS light may illuminate, each with different causes and solutions, as detailed below: Condition 1: ABS warning light stays on (most common). Cause 1: The ABS 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 computer from determining the vehicle's speed or the wheel's slip rate, thereby failing to issue appropriate commands to adjust braking. Solution: Clean the dirt from the speed sensor and adjust the gap between the sensor and the signal ring to restore normal function. Cause 2: Poor signal quality due to loose connections in the system wiring or poor contact in the ABS relay, leading to system failure. Solution: Check the wiring connections and reconnect any loose parts. Condition 2: ABS warning light intermittently illuminates but turns off when accelerating. Cause: When multiple vehicle electrical devices are in use, the battery voltage drops below 10.5V. As the engine speed increases, the 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, and examine the power supply (e.g., voltage relay or poor power contact). Condition 3: ABS warning light stays on 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 electrical connection in the ABS hydraulic valve body; ABS computer malfunction. Solution: Loosen and then retighten the grounding screws on the hydraulic valve body, cleaning the contact surfaces if necessary. Check for enlarged gaps in the connectors. Replace the ABS or ABS/ASR computer if needed. Condition 4: ABS warning light comes on during high-speed driving. Cause: The ABS computer detects a significant discrepancy between the rear and front wheel speed signals 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, which can typically be found on the label near the fuel cap. Condition 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch; poor internal contact in the brake light. Solution: Start the engine, press the brake pedal, and manually push the brake switch linkage down to its limit. Release the brake pedal to complete the self-setting process. Replace the brake light switch if necessary. If the ABS warning light is on, 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.

[BeauLee]

Having driven Golf models for decades, I've encountered the ABS warning light issue quite often. Most cases stem from faulty wheel speed sensors - those components mounted near the wheel hubs easily accumulate dust or metal shavings that interfere with signals, especially noticeable after rainy or muddy road conditions. Low brake fluid level can also trigger it because the system can't monitor pressure properly; other possibilities include loose wiring connections, worn-out short circuits, or rarely, a failed ABS control unit. When the light comes on, while the brakes still function, the ABS feature deactivates - wheels may lock during emergencies, increasing braking distance, which poses significant risks particularly on slippery surfaces. My routine check involves: inspecting sensor cleanliness under the car, topping up brake fluid to proper reservoir levels, and if unresolved, using OBD tools to read trouble codes for precise diagnosis before professional repair. Never delay fixes - safety comes first, and regret after accidents is too late.