Code 25 - Left Front Wheel Speed Sensor Fault

Toothed wheel generates a voltage pulse as it moves past sensor. EBTCM/EBCM uses these pulses to determine wheel speed. EBTCM/EBCM uses wheel speed sensor signal to calculate vehicle reference speeds and speed, acceleration and slip values for each wheel. These values are used to determine when anti-lock control is needed. Code 25 is set if there is a short to voltage or ground in circuits No. 830 or 873, or faulty speed sensor. Testing for this fault occurs with vehicle in motion.

1. Checks if code resets during road test.
2. Use Tech 1 to check for sources of induced electrical noise.
3. Checks for damaged wheel speed sensor circuit shield.
4. Checks for intermittent opens/shorts in wheel speed sensor circuits and cables.
5. Checks for proper resistance in sensor.
6. Checks for a short to battery in either speed sensor circuit wires.
7. Checks for a short between speed sensor circuit wires.
8. Checks for a short to ground in speed sensor input circuit wire.
9. Checks wiring and connectors for intermittents.

Fig 1: Code 25 - Schematic

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 25 - Diagnostic Flowchart (1 Of 2)

Courtesy of GENERAL MOTORS CORP.

Fig 3: Code 25 - Diagnostic Flowchart (2 Of 2)

Courtesy of GENERAL MOTORS CORP.