Circuit Description

Toothed wheel generates a voltage pulse as it moves past sensor. EBCM uses these pulses to determine wheel speed. The amount of voltage generated in each pulse depends on air gap between sensor and toothed wheel and wheel speed.

EBCM uses wheel speed sensor signal to calculate vehicle reference speeds and individual speed, acceleration and slip values for each wheel. These values are used to determine when anti-lock control is needed.

EBCM performs 2 basic types of checks on wheel speed sensors: sensor continuity and sensor output.

1. Determines if code stored is due to a current fault. Current wheel speed sensor faults will be detected when vehicle is driven and reaches speed of 4 MPH. If ANTI-LOCK light comes on, fault is current.
2. Checks for open or short in wheel speed sensor wiring or sensor coil.
3. Checks for conditions that may cause intermittent code setting.

Fig 1: Code 25

Courtesy of GENERAL MOTORS

Fig 2: Code 25: Ckt Diag. (Reatta, Riviera, Toronado, Trofeo)

Courtesy of GENERAL MOTORS

Fig 3: Code 25: Diagnostic Flow Chart (1 of 2)

Courtesy of GENERAL MOTORS

Fig 4: Code 25: Diagnostic Flow Chart (2 of 2)

Courtesy of GENERAL MOTORS