Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC B2647: Ambient Light Sensor Circuit LowDTC B2648: Ambient Light Sensor Circuit High
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Ambient Light Sensor Circuit Signal | B2647 | B2648 | B2648 | -- |
Ambient Light Sensor Low Reference | 1 | B2648 | 1 | -- |
Daytime Running Lamp Control Circuit Signal | B2602 | B2602 | B2603 | -- |
Daytime Running Lamp - Left Voltage Supply | 2 | 2 | 2 | -- |
Daytime Running Lamp - Right Voltage Supply | 2 | 2 | 2 | -- |
Headlamp - Left Voltage Supply | 1 | 1 | 1 | -- |
Headlamp - Right Voltage Supply | 1 | 1 | 1 | -- |
Daytime Running Lamp Ground | -- | 2 | -- | -- |
Headlamp - Left Front Ground | -- | 1 | -- | -- |
Headlamp - Right Front Ground | -- | 1 | -- | -- |
1. Headlamps Malfunction 2. Daytime Running Lamps Malfunction | ||||
Circuit/System Description
The ambient light sensor is used to monitor outside lighting conditions. The ambient light sensor provides a voltage signal that will vary between 1.75 volts and 4.9 volts depending on outside lighting conditions. The body control module (BCM) provides a low reference ground to the ambient light sensor. The body control module monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either daytime running lights (DRL) or automatic lamp control (ALC) when the headlamp switch is in the AUTO position. In daylight conditions the BCM will command the DRLs ON. During low light conditions the BCM will command the low beam headlamps ON. Any function or condition that turns on the headlamps will cancel DRL operation.
Conditions for Running the DTC
The system voltage must be between 9-16 volts.
Conditions for Setting the DTC
B2647
When the ambient light sensor signal voltage is less than 1.75 volts.
B2648
When the ambient light sensor signal voltage is greater than 4.9 volts.
Action Taken When the DTC Sets
The ALC will remain always ON or always OFF in any ambient light state.
Conditions for Clearing the DTC
| • | This DTC will clear immediately after the condition for setting the fault is corrected. |
| • | A history DTC will clear after 100 consecutive ignition cycles without a fault present. |
Reference Information
Schematic Reference
Headlights/Daytime Running Lights (DRL) Schematics
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Ignition ON, observe the scan tool ambient light sensor parameter. The reading should be between 1.75- 4.9 volts.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the ambient light sensor.
- Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit terminal B and ground.
- Ignition ON, verify the scan tool ambient light sensor parameter is between 1.75-4.9 volts.
- Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool ambient light sensor parameter is less than 0.5 volts.
- If all circuits test normal, test or replace the ambient light sensor.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the BCM. |
| ⇒ | If less than 1.75 volts, test the signal circuit terminal A for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
| ⇒ | If more than 4.9 volts, test the signal circuit terminal A for a short to voltage. If the circuit tests normal, replace the BCM. |
| ⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, programming, and setup |
