Antilock Braking System (ABS)

DTC 26 RF Excessive Wheel Speed Variation:

DTC 26 Right Front Excessive Wheel Speed Variation (2 Of 3):

DTC 26 RF Excessive Wheel Speed Variation (3 Of 3):

Right Front Excessive Wheel Speed Variation:

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 26 can be set when the brake is "OFF." The purpose of this test is to detect a situation in which the right front wheel acceleration or deceleration is beyond specified limits.

Action Taken:
A malfunction DTC is stored, ABS is disabled and the "ABS" warning lamp is turned "ON."

DTC Chart Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks wheel speed sensor for proper resistance value.
2. Ensures the wheel speed sensor is not shorted to ground.
3. Ensures the wheel speed sensor is not shorted to voltage.
4. Ensures that DTC 26 was not set due to a poor connection at the EBCM or physical damage of the circuitry.
5. Checks for proper voltage at the wheel signal low speed sensor harness connector.
6. Checks for proper voltage at the wheel signal high speed sensor harness connector.
7. Tests for a short between the wheel signal high and wheel signal low circuits.
8. Checks for an open in the wheel signal low circuit.
9. Checks for an open in the wheel signal high circuit.
10. Checks for proper resistance of the wheel speed sensor.
11. Ensures that the wheel speed sensor circuitry is not shorted to ground.
12. Ensures the wheel speed sensor is not shorted to ground.

Diagnostic Aids:
An "intermittent" malfunction is most likely 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 amber warning lamp is "ON" only during moist environmental changes, (rain, snow, vehicle wash) all wheel speed sensor circuitry should be thoroughly inspected for water intrusion. Use the following procedure. Spray down the suspected area with 5% salt water solution (two teaspoons of salt to 12 oz. of water). Drive vehicle above 24 km/h (15 mph) for at least 30 seconds. If DTC returns immediately, replace suspected harness.

Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.

A careful visual inspection of the toothed ring, CV joint, bearing and wheel speed sensor for physical damage should also be performed. If DTC sets at the same mph every time and wheel speed variation is noted above this mph on the Tech 1, the speed ring is most likely damaged. This can occur at any speed.

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 harness.

If wheel speed sensor harness shows evidence of water intrusion, inspect wheel speed sensor for water intrusion. If water intrusion is evident, replace wheel speed sensor.