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 B2646: Ambient Light Sensor Circuit PerformanceDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Ambient Light Sensor Signal | B2646 | B2646 | B2646 | -- |
Driver Sun Load Sensor Signal | B0184 | B0184 | B0184 | -- |
Passenger Sun Load Sensor Signal | B0189 | B0189 | B0189 | -- |
Left Front Turn Signal Lamp Control | B3948 02 | B3948 05 | B3948 05 | -- |
Right Front Turn Signal Lamp Control | B3949 02 | B3949 05 | B3949 05 | -- |
Sunload Sensor Assembly Low Reference | -- | B0184 or B0189 | B0184 or B0189 | -- |
Turn Signal Lamp - LF Ground | -- | 1 | 1 | -- |
Turn Signal Lamp - RF Ground | -- | 1 | 1 | -- |
1. Turn Signal Lamps and/or Indicators 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 0.09 and 4.9 volts depending on outside lighting conditions. The HVAC control module provides a low reference ground and a 5-volt reference signal to the ambient light sensor. The HVAC 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. The HVAC control module sends a signal to the body control module (BCM) via serial data commanding the BCM to turn the front turn signal lamps on steady (non-flashing). Any function or condition that turns on the headlamps will cancel the DRL operation. With the turn signal/multifunction switch in the OFF position, the turn signal lamps will either be turned ON or OFF after a 30 second delay, depending on whether daylight or low light conditions are sensed by the ambient light sensor.
Conditions for Running the DTC
Battery voltage must be between 9-16 volts.
Conditions for Setting the DTC
The HVAC control module detects the ambient light sensor signal circuit is less than 5 counts (0.09 volt) or greater than 250 counts (4.75 volts) for 3 consecutive tests.
Actions Taken When the DTC Sets
The HVAC control module defaults to low light status.
Conditions for Clearing the DTC
| • | The condition responsible for setting the DTC no longer exists. |
| • | A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred. |
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 Testing
- Ignition OFF, disconnect the harness connector at the sunload sensor assembly.
- Ignition OFF, scan tool OFF, doors CLOSED test for less than 20 ohms between the low reference circuit terminal C and ground.
- Ignition ON, verify the scan tool Ambient Light Sensor parameter is greater than 250 counts.
- Install a 3A fused jumper wire between the signal circuit terminal D and the low reference circuit terminal C. Verify the scan tool Ambient Light Sensor parameter is less than 5 counts.
- If all circuits test normal, replace the sun load sensor assembly.
| ⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If less than the specified range, test the signal circuit terminal D for a short to ground. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | 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 HVAC control module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for HVAC control module replacement, setup, and programming |
