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 0.2 and 4.9 volts depending on outside lighting conditions. The HVAC control module provides a low reference ground and a 5-volt reference signals 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 class 2 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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B2646 Ambient Light Sensor Circuit Performance
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 (0.2 volts) 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. |
| • | You issue a scan tool CLEAR DTCs command. |
| • | A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics Connector End View Reference: Master Electrical Component List | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the Photocell parameter is within the specified range? | 50-250 Counts | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
3 |
Does the scan tool indicate that the Ambient Light Sensor parameter is less than the specified value? | 50 Counts | Go to Step 4 | Go to Step 8 |
4 |
Does the scan tool indicate that the Ambient Light Sensor parameter is greater than 60 counts? | Go to Step 5 | Go to Step 6 | |
5 | Test the low reference circuit of the sunload sensor for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 8 |
6 | Test the low reference circuit of the sunload sensor for a short to ground, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 7 |
7 | Test the ambient light sensor signal circuit of the sunload sensor for a short to ground, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 |
8 | Test the ambient light sensor signal circuit of the sunload sensor for a short to battery positive voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9 |
9 | Inspect for poor connections at the harness connector of the sunload sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 |
10 | Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
11 | Replace the sunload sensor. Refer to Sun Load Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
12 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
