For 1990-2009 cars

### Circuit Description

The body control module (BCM) directly sends a reference voltage to the instrument panel (I/P) dimmer switch which is then reduced based on the I/P dimmer switch position and monitored as a signal to the BCM. The BCM uses this signal to directly control the desired level of I/P illumination lamp intensity.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC 2624 Dimming Display Pulse Width Modulation (PWM) Input Circuit Open

### Conditions for Running the DTC

The battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

When the BCM monitors a signal voltage equal to or greater than 4.86 volts for more than one second

### Action Taken When the DTC Sets

The I/P illumination lamp dimming will not operate.

### Conditions for Clearing the MIL/DTC

• | This DTC will clear on current status after the condition for setting the fault is corrected.

• | A history DTC will clear after 100 consecutive ignition cycles without a fault present.

• | History and current DTCs can be cleared using a scan tool.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step tests for the proper operation of the circuit in the low voltage range.

2. This step tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

3. This step tests for a short to voltage in the signal circuit.

4. This step tests for a high resistance or an open in the low reference circuit.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Interior Lights Dimming Schematics Connector End View Reference: Lighting Systems Connector End Views or Data Communication Connector End Views
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. With the scan tool, observe the Dimming Potentiometer input data parameter in the body control module (BCM) Data List.

Does the scan tool indicate that the Dimming Potentiometer input data parameter is within the specified range?

0.6-4.5 V

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the headlamp and panel dimmer switch.
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, observe the Dimming Potentiometer input data parameter.

Does the scan tool indicate that the Dimming Input data parameter is greater than the specified value?

4.5 V

Go to Step 10

Go to Step 4

4 |

1. Turn OFF the ignition.
2. Connect a 3-amp fused jumper wire between the connector terminals of the low reference circuit and the signal circuit of the headlamp and panel dimmer switch.
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, observe the Dimming Potentiometer input data parameter.

Does the scan tool indicate that the Dimming Potentiometer input data parameter is less than the specified value?

4.86 V

Go to Step 5

Go to Step 8

5 |

1. Disconnect the fused jumper wire.
2. Measure the voltage between the connector terminals of the low reference circuit and the signal circuit of the headlamp and panel dimmer switch.

Does the voltage measure less than the specified value?

5.15 V

Go to Step 6

Go to Step 7

6 |

1. Turn OFF the ignition.
2. Disconnect the negative battery cable.
3. Measure the resistance from the low reference circuit of the headlamp and panel dimmer switch connector and a good ground.

Does the resistance measure less than the specified value?

5 ohms

Go to Step 12

Go to Step 11

7 | Test the signal circuit of the headlamp and panel dimmer switch for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13
8 | Test the signal circuit of the headlamp and panel dimmer switch for a open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 9
9 | Test the low reference circuit of the headlamp and panel dimmer switch for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13
10 | Test the signal circuit of the headlamp and panel dimmer switch for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13
11 |

1. Disconnect the body control module.
2. Test the low reference circuit of the headlamp and panel dimmer switch for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

12 | Inspect for poor connections at the harness connector of the headlamp and panel dimmer switch. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14
13 | Inspect for poor connections at the harness connector of the BCM. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15
14 | Replace the headlamp and panel dimmer switch. Refer to Headlamp Switch Replacement . Did you complete the replacement? | -- | Go to Step 16 | --
15 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 16 | --
16 |

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