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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 DTC 12, signaling beginning of DTC display.
  3. Each stored DTC will be displayed 3 times. After all DTCs have been displayed, sequence will repeat, starting with DTC 12. If code is present, perform appropriate DIAGNOSTIC TROUBLE CODE (DTC) CHART. See DIAGNOSTIC TROUBLE CODE (DTC) table.
  4. After all diagnosis and repairs are completed, clear DTCs and verify operation. If no DTC is present, go to SYMPTOM DIAGNOSIS.
NOTE: Certain DTCs 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 CODE (DTC)

DTC (1) Definition
12 Diagnostic System Operational
21 Right Front Wheel Speed Sensor Circuit
23 Right Front Wheel Speed Sensor Continuity
25 Left Front Wheel Speed Sensor Circuit
27 Left Front Wheel Speed Sensor Continuity
28 Wheel Speed Sensor Frequency Error
35 Rear Axle (Wheel) Speed Sensor Circuit
37 Rear Axle (Wheel) Speed Sensor Continuity
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
(1) Always perform ABS system functional check before using DIAGNOSTIC TROUBLE CODE (DTC) CHARTS. See Figure .