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Flash Code Diagnostics

  1. Ground pin "H" to pin "A" of DLC connector. See Fig 1 . Connector is located under dash, near middle of instrument panel. Turn ignition on. Diagnostic display mode remains enabled as long as pin "H" is grounded, serial data link communications has not been initiated and vehicle speed is less than 4 MPH.
  2. About 3 seconds after DLC pin "H" is grounded, EBCM will begin flashing ANTI-LOCK light in code sequence. Sequence will begin with Code 12, signaling beginning of fault code display.
  3. Each stored code will be displayed 3 times. After all codes have been displayed, sequence will repeat, starting with Code 12. If code is present, perform appropriate DIAGNOSTIC CODE CHART. See DIAGNOSTIC TROUBLE CODES table.
  4. After all diagnosis and repairs are completed, clear trouble codes and verify operation. If no code is present, go to SYMPTOM DIAGNOSIS.
NOTE: Certain codes and ABS history data can only be read through DLC connector using Tech 1 scan tester.
Fig 1: Identifying DLC Connector Pins
G91F11291Courtesy of GENERAL MOTORS CORP.
DIAGNOSTIC TROUBLE CODES

Code Definition(1)
12 Diagnostic System Operational
21 Right Front Wheel Speed Sensor Fault
22 Right Front Toothed Wheel Frequency Error
25 Left Front Wheel Speed Sensor Fault
26 Left Front Toothed Wheel Frequency Error
35 Rear Axle (Wheel) Speed Sensor Fault
36 Rear Axle Toothed Wheel Frequency Error
41 Right Front Solenoid Valve Fault
45 Left Front Solenoid Valve Fault
55 Rear Solenoid Valve Fault
61 Pump Motor Or Relay Fault
63 Solenoid Valve Relay Fault
71 EBCM Fault
72 EBCM Serial Data Fault
(1) Always perform ABS system functional check before using DIAGNOSTIC CODE CHARTS. See
Figure .