GMobd1BrakeCodes

PROCEDURE:

Diagnostic Trouble Codes (DTC) 's can be displayed by jumping terminals "A" and "H" of the Data Link Connector and observing the flashing of the "BRAKE" warning light. This should only be done when the brake lamp is "ON".

The terminals must be jumped for about 20 seconds before the code will begin to flash. Count the number of short flashes starting from the long flash. Include the long flash as a count. Sometimes the first count sequence will be short. However, subsequent flashes will be accurate. If there is more than one failure, only the first recognized code will be retained and flashed.

NOTES:

DTC's 6, 9 and 10 will only turn the "BRAKE" lamp on while the fault exists. These are soft codes faults and can only be read with the Tech 1 scan tool.

Do not jump terminals "A" to "H" if the "BRAKE" lamp is not on. Jumping the terminals with the "BRAKE" lamp off will set a false DTC 9. This will turn the "BRAKE" lamp on and disable the antilock system.

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    • 1, 11, & 12 ECU Malfunction

    • 2 Open Isolation Valve or Malfunctioning ECU

    • 3 Open Dump Valve or ECU Malfunction

    • 4 Grounded Antilock Valve Reset Switch

    • 5 Eccessive Actuations of the Dump Valve

    • 6 Erratic Speed Signal

    • 7 Shorted Isolation Valve or Faulty ECU

    • 8 Shorted Dump Valve or Faulty ECU

    • 9 Open Circuit to Speed Signal

    • 10 Brake Lamp Switch Circuit

  • 13, 14 and 15 ECU Malfunction

The following is a list of the OBD-I trouble codes for the four wheel anti-lock brake system.

*Code 21: right front speed sensor or circuit open

*Code 22: missing right front speed signal

*Code 23: erratic right front speed signal

*Code 25: left front speed sensor or circuit open

*Code 26: missing left front speed signal

*Code 27: erratic left front speed signal

*Code 29: simultaneous drop-out of front speed sensors

*Code 35: vehicle speed sensor or open circuit

*Code 36: missing vehicle speed sensor signal

*Code 37: erratic vehicle speed sensor signal

*Code 38: wheel speed error

*Codes 41 through 54: control valves

*Codes 61 through 63: reset switches

*Code 65 and 66: open or shorted pump motor relay

*Code 67: open motor circuit or shorted BPMV output

*Code 68: locked motor or shorted motor circuit

*Codes 71 through 74: memory errors

*Code 81: brake switch circuit shorted or open

*Code 86: shorted anti-lock indicator lamp

*Code 87: shorted brake warning lamp