For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diangostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC B1395 03 : Voltage Below Threshold
DTC B1395 07 : Voltage Above Threshold

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
I/P Dimming Voltage Reference | B1395 03 | B1395 07 | B1395 07 | B1395 03, B1395 07
I/P Dimming Control Circuit | B3600 03 | B3600 03 | B3600 07 | B3600 03

### Circuit/System Description

Voltage for the interior backlighting components is supplied from the body control module (BCM). The BCM applies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp dimming switch, which is part of the headlamp switch. When the dimming switch is placed in the desired position, the dimmed voltage setting is applied from the interior lamp dimming switch through the I/P dimming control circuit to the BCM. The BCM then applies the dimmed voltage to the I/P lamps supply voltage circuit and they dim to the correct level.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

#### B1395 03

The BCM detects a voltage that is lower than 0.33 volts on the I/P dimming voltage reference circuit.

#### B1395 07

The BCM detects a voltage that is greater than 4.97 volts on I/P dimming voltage reference circuit.

#### B3600 03

The BCM detects a voltage that is lower than 0.10 volts on the I/P dimming control circuit.

### Action Taken When the DTC Sets

The I/P lamps are not illuminated.

### Conditions for Clearing the DTC

• | The conditions for setting the DTC are no longer present.

• | A history DTC clears after 100 malfunction-free ignition cycles.

• | The BCM receives the clear code command from the scan tool.

### Reference Information

#### Schematic Reference

Interior Lights Dimming Schematics

#### Connector End View Reference

Lighting Systems Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

• | Scan Tool Output Controls

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Verification

Ignition ON, cover the ambient light sensor, vary the interior lamp dimming switch from dim to full bright. The I/P lamps should dim and then become full bright.

### Circuit/System Testing

1. Clear the DTC.
2. Use a scan tool to monitor the Dimming Control Reference Signal data parameter in the BCM data list.

⇒ | If less than 0.33 volts, test the I/P dimming voltage reference circuit for a short to ground or an open/high resistance. If the circuit/connections test normal, replace the BCM.

⇒ | If greater than 4.97 volts, test the I/P dimming voltage reference circuit for a short to voltage. If the circuit/connections test normal, replace the BCM.

3. If the voltage is correct and all circuits/connections test normal, replace the headlamp switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Headlamp Switch Replacement for Switch Replacement Procedure.

• | Control Module References for BCM replacement, setup, and programming