DTC 91

This article has been updated with Bulletin No.: 63-50-11

DTC 91 Open Brake Lamp Switch Circuit During Deceleration:

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

DTC WILL SET WHEN
DTC 91 is set after the Cruise/Shift Interlock/B rake Switch remains open for three deceleration cycles. This fault occurs when: The Power Distribution system does not supply battery voltage to CKT 140. Fuse B6 (Brake LPS/Hazard) is open. Either CKT 17 or CKT 140 has a wiring problem, terminal corrosion, or poor connections. The Cruise/Shift Interlock/Brake Switch is malfunctioning. There is a malfunction in the EBTCM.

ACTION TAKEN
A malfunction DTC is stored, TCS is disabled and the "TRACTION OFF" indicator lamp is turned "ON." ABS remains functional.

DTC CHART TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Checks for Wheel Speed Sensor DTC(s).
2. Indicates if an open circuit exists in the brake switch or brake lamp circuit.
3. Checks for an open in CKT 17.

DIAGNOSTIC AIDS
Possible causes:
^ Open brake switch.
^ Open brake switch circuit fuse.
^ Brake switch misadjusted.

An "intermittent" malfunction is most likely 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 of 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.