High Idle Indicator: Description and Operation

ADR INDICATOR

DESCRIPTION
A constant engine speed (ADR) indicator is standard equipment on all instrument clusters, but is only functional on vehicles equipped with the optional ADR switch. The ADR indicator is located near the lower edge of the instrument cluster, to the right of the multi-function indicator display. The ADR indicator consists of the text "ADR" imprinted within a rectangular cutout 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 text to appear silhouetted against an amber field 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 ADR indicator is serviced as a unit with the instrument cluster.

OPERATION
The constant engine speed (ADR) indicator gives an indication to the vehicle operator concerning the operating status of the constant engine speed (ADR) feature. The ADR 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 Engine Control Module (ECM) over the Controller Area Network (CAN) data bus. The ADR indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster detects that the ignition switch is in the On position. Therefore, the LED will always be off when the ignition switch is in any position except On. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn on the traction control indicator for the following reasons:

- Constant Engine Speed (ADR) Indicator Lamp-On Message - Each time the cluster receives an ADR indicator lamp-on message from the ECM, the indicator will be illuminated. The indicator is illuminated when the ADR feature has been activated with the ADR switch, and is turned off when the ADR feature is deactivated with the ADR switch. The ADR indicator will be extinguished if the ADR feature is turned off because the park brake has been released or the vehicle is in motion. The ADR indicator will also be extinguished if the service brake pedal is depressed, but the ADR feature will automatically be restored and the indicator illuminated when the brake pedal is released. The indicator remains illuminated until the cluster receives a lamp-off message from the ECM, or until the ignition switch is turned to the Off position, whichever occurs first.

The ECM continually monitors the constant engine speed (ADR) switch and electronic messages from the Controller Antilock Brake (CAB) concerning the status of the four wheel speed sensors, the park brake switch and the brake lamp switch to determine the correct operating mode for the ADR feature. The ECM then sends the proper lamp-on or lamp-off messages to the instrument cluster. See the owner's manual in the vehicle glove box for the features, use, activation and deactivation of the constant engine speed (ADR) feature. For proper diagnosis of the ADR feature, the ECM, the CAB, the CAN data bus, or the electronic message inputs to the instrument cluster that control the ADR indicator, a diagnostic scan tool is required. Refer to the appropriate diagnostic information.