Code 91/92 - Open Brake Switch Contacts During Deceleration Or When Abs Is Required: Notes

CODE 91/92 test is used to detect an open brake switch in non-ABS mode. When brake pedal is applied, brake switch closes and a voltage signal is sent to EBCM/EBTCM. EBCM/EBTCM looks for this signal to know when brake pedal has been applied. EBCM/EBTCM cannot activate ABS without this signal. Code 91/92 can set if 3 deceleration cycles occur with brake switch off. Code will be stored, ABS will be disabled and ABS warning light illuminated.

Code 91/92 test determines proper operation of brake switch, because ABS is activated when brake switch is on. If brake switch is off, ABS will never be activated. Since this malfunction is difficult to detect under normal braking conditions, this malfunction is only detected when ABS is required. Code 91/92 can set if vehicle's speed is greater than 5 MPH and brake switch was not on and a release was required on 2 channels for 0.5 second. Code will be stored, ABS will be disabled and ABS warning light illuminated.

Fig 1: Code 91/92 Diagnostic Flow Chart Diagnostic Flow Chart Courtesy of General Motors Corp.

1. Determines if brake switch signal is being received by EBCM/EBTCM.
2. Indicates if an open circuit exists in brake switch or brakelight circuit.
3. Isolates open circuit to either brake switch input circuit or EBCM/EBTCM.
4. Ensures malfunction was not due to poor terminal contact.
5. Verifies voltage is available at brake switch.
6. Verifies brake switch is functioning properly.