Pinpoint Tests AE: The Hill Descent Indicator Is Never/Always On

Instrumentation, Message Center and Warning Chimes

Pinpoint Tests

Pinpoint Test AE: The Hill Descent Indicator Is Never/Always On

Normal Operation

When the hill descent control switch is pressed, a ground signal is provided to the Instrument Panel Cluster (IPC) through the hill descent control circuit. The IPC then sends a message to the ABS module over the High Speed Controller Area Network (HS-CAN) communication bus requesting system activation. The ABS module enables the hill descent control system and sends the IPC an indicator request to turn on the hill descent indicator.

The message center provides the specific messages that indicates whether the hill descent system is active mode, fault mode or in the brake cool down mode. For a list of messages, refer to Information And Message Center Information And Message Center description and operation.

If the hill descent control system message is missing for less than 5 seconds, the IPC defaults the hill descent control system message to the last on/off state, based upon the last known good hill descent control system status message.

If the hill descent indicator request message is missing for less than 5 seconds, the hill descent indicator remains in the last indication state (on or off) based upon the last known good message received. If the hill descent indicator request message is missing for more than 5 seconds or longer, the IPC sets DTC U0121:00 and defaults the hill descent indicator off.

This pinpoint test is intended to diagnose the following:

- ABS module
- IPC

PINPOINT TEST AE: THE HILL DESCENT INDICATOR IS NEVER/ALWAYS ON

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AE1 CHECK THE HILL DESCENT CONTROL MODE FUNCTION

- Drive the vehicle between 3 km/h (2 mph) and 32 km/h (20 mph) on a downhill grade and activate the hill descent control system mode.
- Does the hill descent control system function correctly and slow the vehicle?

Yes
GO to AE2.

No
REFER to Vehicle Dynamic Systems Testing and Inspection to diagnose the hill descent system.

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AE2 CARRY OUT THE IPC WARNING LAMPS COMMAND USING THE SCAN TOOL

- Ignition ON.
- Enter the following diagnostic mode on the scan tool: IPC DataLogger.
- Select the IPC hill descent indicator (HDC_ACTIVE) active command. Command the hill descent indicator on and off. Observe the hill descent indicator.
- Does the hill descent indicator illuminate when commanded on, and turn off when commanded off?

Yes
GO to AE3.

No
INSTALL a new IPC. REFER to Instrument Panel Cluster (IPC) Instrument Panel Cluster (IPC). TEST the system for normal operation.

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AE3 RETRIEVE THE RECORDED DTCs FROM THE IPC SELF-TEST

- Check for recorded DTCs from the IPC self-test.
- Is DTC U0121:00 recorded?

Yes
GO to Pinpoint Test BD. Pinpoint Tests BD: DTC U0121:00

No
GO to AE4.

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AE4 RETRIEVE THE RECORDED DTCs FROM THE ABS MODULE SELF-TEST

- Check for recorded ABS module DTCs from the self-test.
- Are any DTCs recorded?

Yes
REFER to Vehicle Dynamic Systems Testing and Inspection.

No
INSTALL a new ABS module. REFER to Vehicle Dynamic Systems Service and Repair. TEST the system for normal operation.

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