Code 21 - Right 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.

1. Checks if code resets during a 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 correct 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 short to ground in speed sensor input circuit wire.
9. Checks wiring and connections for intermittents.

Fig 1: Code 21 - Schematic

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 21 - Diagnostic Flowchart (1 Of 2)

Courtesy of GENERAL MOTORS CORP.

Fig 3: Code 21 - Diagnostic Flowchart (2 Of 2)

Courtesy of GENERAL MOTORS CORP.