Circuit Description
The headlamp automatic control ambient light sensor is a photo-electric cell that provides two inputs to the heater and A/C control system. The input for the sunload is at terminal 3 of the heater and A/C control. This is used by the controller for temperature control compensation based on additional heat from the sun (sunload.) The input for the twilight sentinel is at terminal 2. The twilight sentinel input is then processed by the controller and sent to the body control module (BCM).
Conditions for Setting the DTC
The heater and A/C control continuously monitors CKT X812. DTC 39 will set when the circuit stays above 5.5 V for 200 ms.
Action Taken When the DTC Sets
| • | Stores a DTC 39 in the heater and A/C control memory. |
| • | The system will default to a assumed value of no solar heat (darkness). |
Conditions for Clearing the DTC
| • | The conditions for the fault are no longer present. |
| • | Using a scan tool. |
| • | A history DTC will clear after 20 consecutive ignition cycles if the condition for the fault is no longer present. |
Diagnostic Aids
If condition not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the DTC 39 is Current? | -- | Go to Step 3 | Go to Diagnostic Aids |
Does the voltage measure greater than the specified value? | 5.5 V | Go to Step 4 | Go to Step 5 | |
4 | Test the 5 volt reference circuit of the headlamp automatic control ambient light sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 6 |
5 | Inspect for poor connections at the harness connector of the headlamp automatic control ambient light sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 |
6 | Inspect for poor connections at the harness connector of the heater and A/C controls. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 |
7 | Replace the headlamp automatic control ambient light sensor. Refer to Sun Load Sensor Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- |
8 |
Important: Perform the recalibration procedure for the heater and A/C controls. Replace the heater and A/C controls. Refer to HVAC Control Module Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
