What causes the ABS warning light to stay on in an old Buick Excelle?

[DiLily]

ABS warning lights can indicate various conditions, each with different causes and solutions, as detailed below: Condition 1: ABS warning light stays on (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 speed signals. This prevents the ABS control module from determining vehicle speed or wheel slip rate, thus failing to issue appropriate braking commands. Solution: Clean 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 ABS relay contact causing signal issues. Solution: Inspect wiring connections and secure any loose connections. Condition 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: Battery voltage drops below 10.5V when multiple electrical components are in use. The light extinguishes when engine RPM increases and voltage rises. Possible low voltage supply to ABS system due to poor connections or grounding. Solution: Check battery specific gravity, charging system, and power supply (including voltage relay and connections). Condition 3: ABS warning light remains on after engine start until ignition is turned off. Cause: Poor grounding of ABS hydraulic valve body; loose wiring connections at valve body; ABS control module failure. Solution: Loosen and retighten valve body ground screw (clean contact surface if needed); inspect connector gaps; replace ABS or ABS/ASR control module if necessary. Condition 4: ABS warning light illuminates during high-speed driving. Cause: ABS control module detects significant speed difference between front and rear wheels; incorrect tire or wheel specifications. Solution: Verify proper tire and wheel specifications (refer to fuel filler door label). Condition 5: ABS warning light intermittently flashes. Cause: Improper brake light switch adjustment; internal contact issues in brake lights. Solution: With engine running, press brake pedal and manually push switch lever downward to reset position; replace brake light switch if needed. When the ABS warning light is illuminated, continued driving is not recommended. An active ABS fault means the anti-lock braking system is compromised. During emergency braking, locked wheels could cause loss of vehicle control, preventing proper deceleration or steering correction - creating significant safety risks.