Diagnostic Aids

Make thorough inspection of wheel speed sensor circuitry. Pay particular attention to connectors, since connectors are the most likely area for problems.
ABS system is sensitive to ring damage. Inspect sensor ring for tooth damage or out-of-round condition. Ensure gap between sensor and sensor ring is .025-.070" (.64-1.78 mm).
Measure resistance between sensor terminals. Resistance should be 1650-1800 ohms.
Connect Tech 1 scan tester. Spin wheel by hand while monitoring wheel speed. Compare Tech 1 scan tester indications with those from other wheels.
Suspected intermittents or opens at connectors can be detected with diagnostic service probe which permits voltage to be measured on wires without unplugging connectors. Ensure terminals make good connection.
When diagnosing intermittent problems, select MALF HISTORY from Tech 1 scan tester ABS menu. Supplemental data can be used to duplicate problem.

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 23 - Diagnostic Flowchart (2 Of 2)

Courtesy of GENERAL MOTORS CORP.