Retrieving Codes

NOTE: Perform DIAGNOSTIC CIRCUIT CHECK chart under TROUBLE SHOOTING CHARTS . See Figure.

If using Tech 1 for retrieving codes, go to step 3). If using ANTILOCK light for retrieving codes, turn ignition on. Using a jumper wire, connect terminal "H" to terminal "A" in ALDL connector. See Fig 1. System will repeat trouble code(s) as long as ALDL connector terminals are jumpered.
Trouble codes will begin displaying by a flashing ANTILOCK warning light. As an example, Code 25 would be displayed by ANTILOCK warning light flashing 2 times, followed by a pause, then flashing 5 more times. See 4WAL FAULT CODES table for diagnosis. See CLEARING FAULT CODES to erase stored trouble codes. If no fault codes are present, see 4WAL SYMPTOM DIAGNOSIS table.
Turn ignition off. Connect Tech 1 to ALDL connector. Access 4WAL brake trouble codes with Tech 1. Tech 1 will display trouble code(s). Repair trouble codes in order they appear. See 4WAL FAULT CODES table for diagnosis. See CLEARING FAULT CODES for erasing stored trouble codes. If no fault codes are present, see 4WAL SYMPTOM DIAGNOSIS table.

Fig 1: Identifying ALDL Connector Terminals

Courtesy of GENERAL MOTORS CORP.

4WAL SYMPTOM DIAGNOSIS

Symptom

Perform Chart

ANTILOCK Light On

ANTILOCK LIGHT ON (Fig. Figure)

ANTILOCK Light Off

ANTILOCK LIGHT OFF (Fig. Figure)

Brake Pedal Pulses ⁽¹⁾

BRAKE PEDAL PULSES (Fig. Figure)

Wheel Pull During Hard Braking ⁽¹⁾

WHEEL PULL DURING HARD BRAKING (Fig. Figure)

⁽¹⁾	These conditions must exist with no fault codes stored.

4WAL FAULT CODES

Fault Code

Description

21, 25, 31 or 35 ⁽¹⁾

Speed Sensor Failure Or Open Circuit

22, 26, 32 Or 36 ⁽²⁾

Missing Speed Signal

23, 27, 33 Or 37 ⁽³⁾

Erratic Speed Sensor

Erratic Speed Sensor Signal (2 Dropouts Above 20 MPH)

Simultaneous Dropout Of All 4 Speed Sensors Above 8 MPH

35 ⁽⁴⁾

Speed Sensor Failure Or Open Circuit

36 ⁽⁴⁾

Missing Speed Sensor Signal

37 ⁽⁴⁾

Erratic Speed Sensor Signal

Speed Sensor Error

41-54

Control Valves

61, 62 Or 63

Reset Switches

65 & 66

Motor Relay Open Or Shorted

67 ⁽⁵⁾

Pump Motor Circuit Open Or EHCU Output Shorted

68 ⁽⁵⁾

Pump Motor Locked Or Motor Circuit Shorted

71-74

Memory Errors

Brake Switch Circuit Open Or Shorted

ANTILOCK Light Shorted

BRAKE Light Shorted

⁽¹⁾	"C" and "K" series vehicles will only display Codes 21 and 25.

⁽²⁾	"C" and "K" series vehicles will only display Codes 22 and 26.

⁽³⁾	"C" and "K" series vehicles will only display Codes 23 and 27.

⁽⁴⁾	Applies only to "C" and "K" series vehicles.

⁽⁵⁾	Codes 67 and 68 use the same trouble shooting flow chart.