Code 21 & Code 22 - Front Wheel Speed Is Zero: Notes

Code 21 - Left Front Wheel
Code 22 - Right Front 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/EBTCM uses this signal to compare individual wheel speed data and to detect wheel lock-up.

Code 21/22 can set when vehicle is not in an ABS stop. Code will set if EBCM/EBTCM detects zero MPH speed at left or right front wheel, while remaining wheels are turning at greater than 5 MPH and operating correctly. 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. For identification of circuits and terminals referenced in charts and text, see WIRING DIAGRAM .

Fig 1: Code 21/22 - Diagnostic Flow Chart

Courtesy of GENERAL MOTORS CORP.

Checks for apparent physical damage that may cause code to set.
Checks if sensor resistance is correct.
Verifies if sensor can generate appropriate output signal.
Ensures sensor circuitry is not shorted.
Ensure malfunction is not due to physical damage.