What causes the ABS light to come on in a Sunny?

[ValentinaDella]

There are multiple conditions under which the ABS light may illuminate, each with different causes and solutions, as detailed below: Condition 1: ABS warning light remains constantly lit (most common). Cause 1: The ABS wheel speed sensor's detection area is covered by mud, dirt, 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 contaminants from the wheel speed sensor and adjust the gap between the sensor and the signal ring to restore normal function. Cause 2: Poor signal transmission due to loose system wiring connections or faulty ABS relay contacts, leading to system malfunction. Solution: Inspect wiring connections and reconnect any loose parts. Condition 2: ABS warning light intermittently illuminates but turns off during acceleration. Cause: When multiple electrical components are in use, the battery voltage drops below 10.5V. As engine speed increases and voltage rises, the ABS warning light turns off. 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 the power supply (e.g., voltage relay or poor power contact). Condition 3: ABS warning light remains lit after engine startup until the engine is turned off (IGFF). Cause: Poor grounding connection of the ABS hydraulic valve body; faulty wiring connections at the ABS hydraulic valve body; malfunction of the ABS control unit. Solution: Loosen and then retighten the grounding screw of the hydraulic valve body, cleaning the contact surface if necessary; check for enlarged terminal gaps; replace the ABS or ABS/ASR control unit. Condition 4: ABS warning light illuminates during high-speed driving. Cause: The ABS control unit detects a significant discrepancy between rear and front wheel speed signals during high-speed driving; incorrect tire or wheel rim specifications. Solution: Refer to the vehicle's specified tire and wheel rim sizes, typically listed on the fuel tank cap label. Condition 5: ABS warning light intermittently illuminates. Cause: Improper adjustment of the brake light switch; poor internal contact in the brake light. Solution: With the engine running, press the brake pedal and manually push the brake switch linkage down fully, then release the pedal to reset its position; replace the brake light switch if necessary. When the ABS warning light is on, it is advisable to avoid further driving. An illuminated ABS light indicates a malfunction in the anti-lock braking system. During emergency braking, locked wheels can cause the vehicle to skid uncontrollably, preventing the driver from slowing down or adjusting the vehicle's path, posing significant safety risks.