DTC 91

DTC 91 Open Brake Switch During Deceleration:

Circuit Description:
This DTC is used to detect an open brake switch in the non-ABS mode. The EBCM looks for deceleration rates that would indicate braking action and verifies this assumption by requiring several repeats of this detection method. In each case, ABS will not be available since no brake switch is seen.

DTC Will Set When:
DTC 91 can be set if three deceleration cycles occur with the brake switch "OFF."

Action Taken:
A malfunction DTC is stored, ABS is disabled and the ABS warning lamp is turned "ON."

DTC Chart Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Indicates if the brake switch signal is being received by the EBCM.
2. Indicates if an open circuit exists in the brake switch or brake lamp circuitry.
3. Isolates the open circuit to either the brake switch input circuitry, or the EBCM.
4. Ensures malfunction was not due to poor terminal contact.
5. Verifies that voltage is available at the brake switch.
6. Verifies that the brake switch is functioning properly.

Diagnostic Aids:
An "Intermittent" malfunction may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.

The frequency of the malfunction can be checked by using the enhanced diagnostic function of the Tech 1.

Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.