What does it mean when the ABS light is on in a Jetta?

[LeChase]

When the ABS light is displayed on a car, it indicates a malfunction in the vehicle's anti-lock braking system. During emergency braking, if the wheels lock up, the vehicle may lose control and skid, preventing the driver from slowing down or adjusting the vehicle's trajectory, which poses a significant safety hazard. There are several states in which the ABS light may illuminate, each with different causes and solutions. The details are as follows: State 1: The ABS warning light remains constantly lit (most common). Cause 1: The ABS wheel speed sensor's sensing area is covered by dirt, mud, or other contaminants, affecting the sensor's ability to detect the corresponding speed signal. This prevents the ABS computer from determining the vehicle speed and 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 signal ring to restore normal function. Cause 2: Poor signal 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. State 2: The 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 indicator 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 verify the power supply (e.g., voltage relay or poor power contact). State 3: The ABS warning light remains lit after the engine starts 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 valve body's wiring, or a faulty ABS computer. Solution: Loosen and then retighten the grounding screw on the hydraulic valve body, clean the contact surface if necessary, check for enlarged gaps in the connectors, and replace the ABS or ABS/ASR computer if needed. State 4: The ABS warning light illuminates during high-speed driving. Cause: During high-speed driving, the ABS computer detects a significant discrepancy between the rear and front wheel speed signals. This may also occur due to incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's tire and wheel rim specifications, as indicated on the label near the fuel tank cap. State 5: The 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, push the brake switch linkage down with your finger, release the brake pedal to complete the self-setting position, or replace the brake light switch.