Brake Warning Lamp

PURPOSE
The vehicle instrument cluster has a red BRAKE warning light to alert the driver to the following conditions:
- Parking brake applied
- Hydraulic failure in either front or rear channel
- ABS warning lamp circuit problem

OPERATION
An ignition switch controlled circuit provides power to the brake warning light in the vehicle instrument cluster. There are three parallel paths to chassis ground to complete the circuit:
- Through the parking brake switch contacts
- Through the combination valve differential switch
- Through the Controller - Antilock Brake (CAB)

The CAB completes the brake circuit for two reasons:
- To Conduct a brake light circuit check at the beginning of each ignition cycle.
- To Alert the driver of an ABS system malfunction related to the foundation brakes.

Self Diagnosis of Lamp Circuit
The CAB checks the brake warning light circuit at the beginning of each ignition cycle.
- If the CAB monitors a high voltage when it attempts to ground the light circuit, it determines that a short exists.
- Diagnostic action for this detected condition includes setting a (88) Indicator Lamp (Red) Circuit trouble code.
- The ABS system will not be inhibited.

Light Illuminates At Start-up
The amber antilock light illuminates at start-up as part of the system self check feature. The light illuminates for 2-3 seconds then goes off as part of the normal self check routine.

Light Remains On After Start-up
An ABS system fault is indicated when the light remains on after start-up. Diagnosis with the flash codes or DRB II scan tool will be necessary to determine the faulty component.

Light Illuminates During Brake Stop
A system fault such as loss of speed sensor signal or solenoid failure, will cause the amber warning light to illuminate. The most effective procedure here is to check for obvious damage first. Then check the electronic components with the DRB II scan tool, or flash codes.