Code 25/26/27/28 - Excessive Wheel Speed Variation: Notes
- Code 25 - Left Front Wheel
- Code 26 - Right Front Wheel
- Code 27 - Left Rear Wheel
- Code 28 - Right Rear Wheel
As toothed ring passes wheel speed sensor, changes in magnetic field causes wheel speed sensor to produce an AC voltage signal whose frequency is proportional to wheel speed. The magnitude of the signal is directly related to wheel speed and proximity of wheel speed sensor to toothed ring, referred to as air gap. EBCM uses this signal to compare individual wheel speed data and to detect wheel lock-up.
Code can set when brake is off. This test detects a situation in which wheel acceleration or deceleration is beyond specified limits. Code will be stored, ABS will be disabled and ABS warning light will be illuminated.
NOTE:
Test numbers refer to numbers on diagnostic chart. Use only 10-megohm (minimum) DVOM for all voltage and resistance tests.
- Identifies a wheel speed sensor for apparent physical damage that may cause code to set.
- Checks if wheel speed sensor resistance is correct.
- Verifies that wheel speed sensor can generate proper output signal.
- Ensures wheel speed sensor circuitry is not shorted.
- Ensures malfunction is not due to physical damage of circuitry.