What causes the ABS light to illuminate in a Volkswagen Santana?

[DelKai]

There are multiple states of the ABS light being on, with different causes and solutions for each state. The details are as follows: State 1: ABS warning light stays on (most common). Cause 1: The ABS speed sensor's sensing part is covered by mud, sludge, 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, thus failing to issue appropriate commands to regulate braking. Solution: Clean the dirt from the speed sensor and adjust the gap between the speed sensor and the signal ring to restore normal function. Cause 2: Loose connections between system lines or poor contact in the ABS relay can cause signal issues, leading to system failure. Solution: Check the line connections and reconnect any loose parts. State 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: When multiple vehicle 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. Another cause is insufficient power supply voltage to the ABS system, such as 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 stays on after engine start and only turns off after engine IGFF. Cause: Poor grounding contact in the ABS hydraulic valve body, poor contact in the ABS hydraulic valve body's wiring connector, or ABS computer failure. Solution: Loosen and then retighten the hydraulic valve body's grounding screw, cleaning the contact surface if necessary. Check if the connector gap has widened, and replace the ABS or ABS/ASR computer if needed. State 4: ABS warning light illuminates during high-speed driving. Cause: During high-speed driving, the ABS computer detects a significant difference between the rear and front wheel speed signals. Incorrect tire or wheel rim specifications may also cause this issue. Solution: Refer to the vehicle's tire and wheel rim specifications, as indicated on the fuel tank cap sticker. State 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch or poor internal contact in the brake light. Solution: Start the engine, press the brake pedal, and use a finger to push the brake switch linkage all the way down. Then release the brake pedal to complete the self-setting position. 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.