What causes the ABS light to illuminate in a Touareg?

[MacChristopher]

There are multiple scenarios where 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 scenario). Cause 1: The ABS wheel speed sensor's sensing area is contaminated by mud, sludge, or other pollutants, interfering with its ability to detect wheel speed signals. This prevents the ABS control module from determining vehicle speed or calculating wheel slip rates, consequently disabling its ability to issue appropriate braking commands. Solution: Clean contaminants from the wheel speed sensor and adjust the gap between the sensor and tone ring to restore normal function. Cause 2: Loose wiring connections or poor contact in ABS relays causing signal disruptions that trigger system faults. Solution: Inspect all wiring connections and securely reconnect any loose terminals. State 2: ABS warning light illuminates intermittently, extinguishing during acceleration. Cause: Battery voltage drops below 10.5V when multiple electrical systems are active. The light extinguishes as engine speed increases voltage. Possible low voltage supply to ABS system due to poor terminal connections or grounding issues. Solution: Check battery specific gravity; inspect charging system; verify power supply components (voltage relays or connection integrity). State 3: ABS warning light remains illuminated after engine start until ignition OFF. Cause: Poor ground connection at ABS hydraulic valve body; faulty wiring harness connector at valve body; ABS control module malfunction. Solution: Loosen and retighten valve body ground screw, cleaning contact surfaces if necessary; inspect connectors for excessive play; replace ABS or ABS/ASR control module if required. State 4: ABS warning light activates during high-speed driving. Cause: ABS control module detects excessive speed differential between front and rear wheels; incorrect tire or wheel rim specifications. Solution: Verify proper tire and wheel rim specifications as indicated on vehicle's fuel filler door placard. State 5: ABS warning light flashes intermittently. Cause: Improper brake light switch adjustment; internal contact failure in brake lights. Solution: With engine running, depress brake pedal while manually pushing brake switch linkage downward to reset position; replace brake light switch if defective. When the ABS warning light is illuminated, continued driving is not recommended. An active ABS fault indicates compromised anti-lock braking functionality. During emergency braking, wheel lock-up may cause uncontrolled skidding, preventing the driver from decelerating or maintaining vehicle trajectory, creating significant safety hazards.