What Causes the ABS Light to Illuminate in a Ford Focus?

[McPaige]

ABS light illumination can occur in various states, with different causes and solutions for each state, as detailed below: State 1: ABS warning light remains constantly illuminated (most common). Cause 1: The ABS wheel speed sensor's sensing area is covered by mud, sludge, or other contaminants, affecting its ability to detect the corresponding speed signal. This prevents the ABS control unit from determining the vehicle speed and 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 tone ring to restore normal function. Cause 2: Poor signal transmission due to loose system wiring connections or faulty ABS relay contacts. Solution: Inspect wiring connections and reconnect any loose parts. State 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: When multiple vehicle electrical components are in use, the battery voltage drops below 10.5V. The ABS warning light turns off as engine speed increases and voltage rises. This may also occur due to insufficient power supply voltage to the ABS system, such as poor terminal contact or grounding issues. Solution: Check battery specific gravity; inspect the charging system; examine power supply components (e.g., voltage relay or poor power contact). State 3: ABS warning light remains illuminated after engine start until engine is turned off (IGFF). Cause: Poor grounding connection of ABS hydraulic valve body; poor electrical connector contact at ABS hydraulic valve body; ABS control unit malfunction. Solution: Loosen and retighten the hydraulic valve body grounding screw, cleaning contact surfaces if necessary; check for enlarged connector gaps; replace ABS or ABS/ASR control unit. State 4: ABS warning light illuminates during high-speed driving. Cause: During high-speed driving, the ABS control unit detects a significant discrepancy between rear and front wheel speed signals; incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's specified tire and wheel rim sizes, typically listed on the fuel filler cap sticker. State 5: ABS warning light intermittently illuminates. Cause: Improper brake light switch adjustment; poor internal contact in brake lights. Solution: With engine running, fully depress brake pedal and manually push the brake switch linkage downward to complete self-setting; replace brake light switch if necessary. When the ABS warning light is illuminated, it is recommended not to continue driving as this indicates a malfunction in the anti-lock braking system. During emergency braking, if wheels lock up, the vehicle may skid uncontrollably, preventing the driver from decelerating or adjusting the vehicle's trajectory, posing significant safety risks.