Antilock Braking System (ABS)

DTC 21, 22, 23 & 24 Wheel Speed Sensor Input Signal = 0:

DTC's 21, 22, 23, & 24 Wheel Speed Sensor Input Signal = 0:

CIRCUIT DESCRIPTION
As a toothed ring passes by the wheel speed sensor, changes in the electromagnetic field cause the wheel speed sensor to produce a sinusoidal (AC) voltage signal whose frequency is proportional to wheel speed. The magnitude of this signal is directly related to wheel speed and the proximity of the wheel speed sensor to the toothed ring, often referred to as the air gap.

DTC WILL SET WHEN
DTC 21, 22, 23, or 24 can be set when the vehicle is not in an ABS or TCS event (if equipped with TCS). If one wheel speed = 0 and the vehicle's reference speed is greater than 8 km/h (5 mph), a malfunction exists.

ACTION TAKEN
A malfunction DTC is stored, ABS/TCS is disabled and the "ANTILOCK" and "TRACTION OFF" Indicator lamps are turned "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step identifies a wheel speed sensor or circuitry that is damaged and visibly apparent.
2. Checks to see that the wheel speed sensor coil is within proper resistance values.
3. Verifies that the wheel speed sensor can generate an appropriate output signal.
4. The 39700 Pinout Box with the 39700-25 adapter cable must be connected before this step is performed. This step ensures that the wheel speed circuitry is not shorted together.
5. Ensures that the malfunction was not due to physical damage.

DIAGNOSTIC AIDS
Possible causes:
^ Wheel speed sensor has low or no output.
^ Excessive air gap, due to worn or damaged wheel speed sensor/bearing assembly.

An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation. The frequency of the malfunction can be checked by using the enhanced diagnostic function of the Tech 1.

If the customer's comments reflect that the ABS or TCS warning lamps are "ON" only during moist environmental changes (rain, snow, vehicle wash), all wheel speed sensor circuitry should be thoroughly inspected for signs of water intrusion. If DTC is not current, clear DTCs and simulate the effects of water intrusion. Use the following procedure. Spray the suspected area with a 5% salt water solution (two teaspoons of salt to 12 oz. of water). Test drive vehicle over various road surfaces (bumps, turns, etc.) above 24km/h (15 mph) for at least 30 seconds. If DTC returns, replace suspected harness.

Resistance of the wheel speed sensor will increase with an increase in sensor temperature.

When replacing a wheel speed sensor, inspect the sensor terminals and harness connector for corrosion and/or water intrusion. If evidence of corrosion or water intrusion exists, replace wheel speed sensor jumper harness. Likewise, if replacing a wheel speed sensor jumper harness, inspect sensor terminals. If evidence of corrosion or water intrusion exists, replace wheel speed sensor.

It is necessary to test drive the vehicle greater than 10 mph for at least 3 seconds to verify that the problem has been corrected.