Technical information

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Technician Guidelines for Antilock Braking Systems

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TABLE 3: COMMON ABS SENSOR PROBLEMS AND CAUSES

PROBLEM CAUSE

Sensor signal is erratic.

Damaged tooth wheel, excessive hub

runout, and/or sensor gap is too wide.

Replace as needed. Check sensor

adjustment, resistance. Check wheel

bearing adjustment.

Open sensor circuit.

Damaged sensor, cable or loose cable

connections. Replace as needed.

Shorted sensor circuit.

Damaged sensor, cable or cable

connections. Replace as needed.

One sensor is not producing a signal

when other sensors are producing

signals, and sensor resistance is within

specification.

Improper air gap at non-producing

sensor. Gaps should not exceed 2 mm

(0.080 in.). Check sensor adjustment.

Check wheel bearing adjustment.

ABS malfunction indicator lamp does not

go out when vehicle reaches speed

needed for minimum or “threshold”

voltage (such as five mph.)

All of the items listed above could be

causes. Also, no tooth wheel or sensor

installed. Install tooth wheel and sensor.

Sensor cap and cables lose elasticity,

swell, or become mechanically sensitive.

Corrosion of bushing, sensor, and/or

sensor clip. Make any necessary

replacements. Check manufacturer’s

recommendations for proper lubricant.

Even if the space between the teeth of the exciter ring is full of

dust and particles from the brake linings, the monitoring

operation is not affected. In fact, the magnetic property of the

dirt in the gaps is similar to that of air. The change in the

magnetic field is determined by the spacing of the teeth of the

exciter ring. The output voltage is unaffected by dirt.

Therefore, an ABS fault cannot be remedied by cleaning the

tooth wheel with compressed air. Dirt in the gaps doesn’t affect

voltage output, so removing it will not remedy an ABS fault.