DTC 91: Open Brake Switch During Deceleration: Description

If EBCM fails to detect stoplight switch input for 3 deceleration cycles, DTC can be set.

1. Turn ignition on. Using scan tool, select ABS data list. Monitor stop light switch on scan tool. Apply light pressure on brake pedal. If scan tool indicates ON within 1" (25 mm) of pedal travel, system is currently functioning correctly. See DIAGNOSTIC AIDS . If scan tool does not indicate ON within 1" (25 mm) of pedal travel, go to next step.
2. With brake pedal pressure still applied, inspect rear brake lights. If brakes lights are illuminated, go to next step. If brake lights are not illuminated, go to step 4).
3. Turn ignition switch to LOCK position. Disconnect EBCM harness connectors. Turn ignition switch on. With brake pedal pressure still applied, measure voltage between ground and terminal No. 21 (Green/White wire) on EBCM 24-pin harness connector. If voltage is 10 volts or less, repair Green/White wire for short to ground. If voltage is greater than 10 volts, replace EBCM.
4. Measure voltage between ground and White/Yellow wire at terminal No. 2 (A/T) or No. 3 (M/T) on brake light switch harness connector. If voltage is 10 volts or less, repair White/Yellow wire for open or short to ground. If voltage is greater than 10 volts, go to next step.
5. While applying pressure to brake pedal, measure voltage between ground and terminal No. 1 (Green/White wire) brake light switch harness connector. If voltage is 10 volts or less, adjust or replace brake switch as needed. If voltage is greater than 10 volts, repair open in Green/White wire.