ASE A4 Suspension and SteeringWheels and Tires Diagnosis and RepairHard
A technician is replacing a wheel bearing assembly on a front-wheel drive vehicle. After installation, the technician notices that the ABS light is illuminated. The wheel bearing assembly included a new wheel speed sensor. What is the MOST likely reason for the ABS light to be on?
- AThe new wheel speed sensor is incompatible with the ABS module.
- BThe brake fluid level is low due to air in the system.
- CThe wheel speed sensor tone ring was damaged during installation.
- DThe lug nuts were not torqued to specification.
Show answer & explanationAnswer & explanation
Correct answer: C. The wheel speed sensor tone ring was damaged during installation.
Damaging the wheel speed sensor tone ring (or reluctor ring) during wheel bearing installation is a common cause of ABS light illumination. The tone ring provides the speed signal to the ABS sensor, and damage can lead to an erratic or missing signal, triggering a fault.
Why the other options are wrong
- A. While possible, a new wheel bearing assembly typically comes with a compatible sensor. Damage during installation is more common.
- B. Low brake fluid or air in the system would trigger the brake warning light, not typically the ABS light directly, unless it's a combined system fault.
- D. Incorrect lug nut torque would primarily cause vibration or wheel loosening, not directly trigger the ABS light.
ABS Tone Ring Damage
The ABS tone ring (reluctor ring), which provides wheel speed data to the sensor, is susceptible to damage during wheel bearing or axle replacement, leading to ABS system faults and an illuminated ABS light.
- Provides wheel speed signal
- Often integrated with wheel bearing or axle
- Damage causes erratic/missing signal, triggering ABS light
Memory trick: Bearing's in, but ABS is out? Check the ring, no doubt!