Electronic Stability Program/Brake Assist System Indicator
ELECTRONIC STABILITY PROGRAM/BRAKE ASSIST SYSTEM INDICATORDESCRIPTION
An Electronic Stability Program/Brake Assist System (ESP/BAS) indicator is standard equipment on all instrument clusters. This indicator is located in the center of the speedometer, in the area below and to the left of the speedometer needle hub.
The ESP/BAS indicator consists of a stencil-like cutout of the text "ESP BAS" in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. An amber Light Emitting Diode (LED) behind the cutout in the opaque layer of the overlay causes the "ESP BAS" text to appear in amber through the translucent outer layer of the overlay when the indicator is illuminated from behind by the LED, which is soldered onto the instrument cluster electronic circuit board.
The ESP/BAS indicator is serviced as a unit with the instrument cluster.
OPERATION
The ESP/BAS indicator gives an indication to the vehicle operator when a problem has been detected in the Electronic Stability Program (ESP)/Brake Assist System (BAS). This indicator is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the Controller Antilock Brake (CAB) and the Front Control Module (FCM) over the Controller Area Network (CAN) data bus.
The ESP/BAS indicator is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the indicator will always be off when the ignition switch is in any position except On or Start. The indicator only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn on the ESP/BAS indicator for the following reasons:
- Bulb Test - Each time the ignition switch is turned to the On position the ESP/BAS indicator is illuminated for about four seconds as a bulb test. The entire bulb test is a function of the CAB.
- ESP/BAS Lamp-On Message - Each time the cluster receives an ESP/BAS lamp-on message from the CAB indicating that a fault has been detected in the ESP/BAS or that the ESP/BAS system has been manually disabled using the ESP/BAS Traction Control System (TCS) switch on the instrument panel, the ESP/BAS indicator will be illuminated. The indicator remains illuminated until the cluster receives an ESP/BAS lamp-off message from the CAB, or until the ignition switch is turned to the Off position, whichever occurs first.
- Actuator Test - Each time the cluster is put through the actuator test, the ESP/BAS indicator will be turned on, then off again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.
The CAB continually monitors the components and circuits of the ESP/BAS system to determine whether the system is in good operating condition and whether or not the system has been manually disabled by the vehicle operator using the ESP/BAS traction control switch. The CAB then sends the proper ESP/BAS lamp-on and lamp-off messages to the instrument cluster.
For proper diagnosis of the traction control switch, the ESP/BAS system, the CAB, the CAN data bus, or the electronic message inputs to the instrument cluster that control the ESP/BAS indicator, a diagnostic scan tool is required.