Code 23/24 - Rear Wheel Speed Is Zero Or Unreasonable: Notes

Code 23 - Left Rear Wheel
Code 24 - 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 23 can set when vehicle is not in an ABS stop. If EBCM detects zero MPH speed at left or right front wheel while remaining wheels are turning at greater than 5 MPH and operating correctly, code will set. 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 23/24 Diagnostic Flow Chart

Courtesy of GENERAL MOTORS CORP.

Identifies damaged circuit.
Checks for proper resistance at rear speed sensor harness connector.
Checks for short between wheel signal high and low circuits.
Checks wheel speed sensor and harness for proper resistance values.