For 1990-2009 cars

### Circuit Description

The instrument panel module (IPM) provides the instrument panel (I/P) dimmer switch with a 5-volt reference voltage and ground. The I/P dimmer switch is a potentiometer that varies the input signal voltage to the IPM. This input determines the intensity level of the back lighting illumination. When the IPM receives the input from the I/P dimmer switch, the IPM will send a GMLAN serial data message to all control modules that have lamps capable of being dimmed, indicating the ON/OFF status and intensity level of the back lighting. The IPM will default to full intensity if the input from the I/P dimmer switch is not within the specified values. For more detailed information concerning interior lighting operation, refer to Interior Lighting Systems Description and Operation .

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B3600 Passenger Compartment Dimming Request Signal Circuit

The vehicle has DTCs including the DTC symptoms. Refer to DTC Symptom Description for more DTC symptoms.

DTC Symptom | DTC Symptom Descriptor
--- | ---
08 | Signal Invalid

### Conditions for Running the DTC

• | The IPM must be powered.

• | The IPM performs this diagnostic test mode every 150 milliseconds.

### Conditions for Setting the DTC

The IPM detects an open, short to ground, or short to voltage in the I/P lamp dimmer switch signal circuit after 450 milliseconds.

### Action Taken When the DTC Sets

The IPM will default to full intensity if the input from the I/P dimmer switch is not within the specified values.

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC no longer exists.

• | You issue a scan tool CLEAR DTCs command.

• | A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.

### Diagnostic Aids

Thoroughly inspect the wiring and connectors. An incomplete inspection of the wiring and connectors may result in misdiagnosis causing part replacement with the reappearance of the malfunction. If an intermittent malfunction exists, refer to Testing for Intermittent Conditions and Poor Connections .

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Interior Lights Dimming Schematics Connector End View Reference: Master Electrical Component List
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Place the headlamp switch in the PARK position.
4. With a scan tool observe the Dimming Pot A/D parameter in the instrument panel module (IPM) inputs list.
5. Turn the instrument panel (I/P) dimmer switch from minimum to maximum intensity.

Does the scan tool indicate the dimming pot A/D parameter is within the specified range as the I/P dimmer switch is changed from minimum to maximum intensity?

25-145 Counts

Go to Step 6

Go to Step 3

3 | Test the I/P lamp dimmer switch signal circuit for an open, short to ground, or short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 4
4 | Test the I/P dimmer switch low reference circuit for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 5
5 | Inspect for poor connections at the harness connector of the I/P dimmer switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7
6 | Inspect for poor connections at the harness connector of the IPM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8
7 | Replace the I/P dimmer switch. Refer to Instrument Panel Lamp Dimmer Switch Replacement . Did you complete the replacement? | -- | Go to Step 9 | --
8 | Replace the IPM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 9 | --
9 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK