Pinpoint Test W: The Rear Fog Lamp Indicator Is Never/Always On

Instrumentation and Warning Chimes

Pinpoint Tests

Pinpoint Test W: The Rear Fog Lamp Indicator Is Never/Always On

Refer to Wiring Diagram Set 60, Instrument Cluster for schematic and connector information. Diagrams By Number

Normal Operation

The Instrument Cluster (IC) receives the rear fog lamp on/off status from the Generic Electronic Module (GEM) over the Medium Speed Controller Area Network (MS-CAN) communication bus. The GEM is hardwired to the headlamp switch. When the rear fog lamps are on, the headlamp switch provides voltage to the fog lamps and the GEM. The GEM monitors the voltage input on the rear fog lamp input circuit and sends a message to the IC to turn on the rear fog lamp indicator.

If the rear fog lamp data is missing for less than 5 seconds, the rear fog lamp indicator remains in the last indication mode (on or off), based upon the last known good data message. If the rear fog lamp data is missing for more than 5 seconds, the IC defaults the rear fog lamp indicator off.

This pinpoint test is intended to diagnose the following:

- Wiring, terminals or connectors
- Rear fog lamp concern
- GEM
- IC



PINPOINT TEST W: THE REAR FOG LAMP INDICATOR IS NEVER/ALWAYS ON

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W1 CARRY OUT THE IC INDICATOR LAMP CONTROL ACTIVE COMMAND USING THE SCAN TOOL


- Ignition ON.
- Enter the following diagnostic mode on the scan tool: IC DataLogger.
- Select the IC rear fog lamp (R_FOG_LMP) active command. Command the rear fog lamp indicator on and off while observing the rear fog lamp indicator.
- Does the rear fog lamp indicator illuminate when commanded on, and turn off when commanded off?

Yes
GO to W2.

No
INSTALL a new IC. REFER to Instrument Cluster (IC) Service and Repair. TEST the system for normal operation.

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W2 CHECK THE REAR FOG LAMP OPERATION


- Turn on the rear fog lamps while monitoring the rear fog lamps.
- Do the rear fog lamps operate?

Yes
GO to W3.

No
REFER to Lighting and Horns.

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W3 CHECK THE REAR FOG LAMP INPUT TO THE GEM


- Turn the rear fog lamps off.
- Ignition OFF.
- Disconnect: GEM C201b.
- Turn the rear fog lamps on.
- Measure the voltage between the GEM C201b-19, circuit 15S-LD13 (GN/OG), harness side and ground.




- Is the voltage greater than 10 volts?

Yes
GO to W4.

No
REPAIR circuit 15S-LD13 (GN/OG) for an open. TEST the system for normal operation.

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W4 CHECK FOR CORRECT GEM OPERATION


- Disconnect the GEM connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect the GEM connectors and make sure they seat correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?

Yes
INSTALL a new GEM. REFER to Body Control Systems. TEST the system for normal operation.

No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.

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