follow the instruction and fix it. God bless you
When a wheel speed sensor (WSS) fails
or there's a problem in the sensor's wiring circuit, it usually
disables the ABS system and causes the ABS warning light to come on.
Loss of a wheel speed signal is a serious problem because the ABS module
needs accurate input from all its sensors to determine whether or not a
wheel is locking up. Without this vital information, the ABS system
can't do its thing.
Wheel speed sensors produce an alternating current (AC) output
voltage that varies in frequency and amplitude with wheel speed. The
faster the wheel turns, the greater the frequency and amplitude of the
sensor's output signal. The strength of the signal can be affected by
resistance in the sensor, resistance in the wiring and connectors,
metallic debris on the end of the sensor, and the air gap between the
sensor and tone ring mounted on the axle, hub, brake rotor, drum or CV
A narrow air gap is usually necessary to induce a strong signal
in the sensor's magnetic windings. Air gaps typically range from .016
in. to as much as .050 in. (0.40 to 1.3 mm) depending on the
application. If the ABS warning light is on and you find a code for a
wheel speed sensor (and the sensor is adjustable), the problem may be
nothing more than too wide an air gap. Use a brass or nonmagnetic
feeler gauge set the gap to the factory recommended specs.
Variations in the air gap can also cause fluctuations in the
sensor's output signal. These may be caused by bad wheel bearings or
missing, broken or chipped teeth on a tone ring. Even minor damage to
the tone ring that's nearly impossible to see can sometimes cause a
problem. One equipment supplier makes a test bench with a magnetic
pickup and oscilloscope to check tone rings on remanufactured FWD axle
shafts. The setup simulates the signal produced in a wheel speed
sensor. Tests have shown that a variation in height of only about .010
inch on a single tooth can cause a noticeable fluctuation in the
sensor's output signal!
WHEEL SPEED SENSOR CHECKS
One way to check a suspicious wheel speed sensor is to
measure its output voltage. One way to do this is to plug a breakout
box into the ABS module's wiring harness and attach the test leads from a
digital volt ohm meter (DVOM) to the appropriate pins for the WSS
A good wheel speed sensor will generally produce an alternating
current (AC) voltage reading of 50 to 700 MV when the wheel is spun by
hand at about one revolution per second. Refer to a shop manual for the
sensor's exact voltage specifications.
A low voltage reading or no reading calls for a direct
measurement of the resistance in the WSS circuit (with the key off).
This should be done through the breakout box to check the entire
circuit. A good wheel speed sensor and circuit will typically have a
resistance of 800 to 1400 ohms (specs vary, so refer to a manual for the
If the sensor circuit has too much resistance, reads open or is
shorted (little or no resistance), measure the resistance across the
sensor itself. If the sensor itself reads within specs, the problem is
in the wiring or connectors. If not, then you have identified a bad
sensor that needs to be replaced.