For 1990-2009 cars

### Circuit Description

The solar/twilight 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 voltage on circuits P11 or P111 significantly rises above 400 mV for 200 ms.

### Action Taken When the DTC Sets

• | Stores a DTC 40 in the heater and A/C control memory.

• | The system will default to a assumed value of no solar heat (darkness).

• | DTCs 10, 12, 14, 26, 39, 55, and 169 may also appear when DTC 40 sets.

### 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

• | In the event that the multiple DTCs set, first follow the repair procedures in the diagnostic table for DTC 40. If some or all of the multiple DTCs reappear after repairing the cause of DTC 40, follow the repair procedures given for the appropriate DTC.

• | 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.

1. This step tests the reference voltage from the heater and A/C control.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: HVAC Schematics
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - HVAC Systems - Automatic
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, observe the DTC list in the Heater and Air Conditioning.

Does the scan tool indicate that the DTC 40 is Current?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Disconnect the headlamp automatic control ambient light sensor connector.
2. Turn ON the ignition, with the engine OFF.
3. Measure the voltage between the sensor ground circuit of the headlamp automatic control ambient light sensor and a good ground.

Does the voltage measure greater than the specified value?

400 mV

Go to Step 4

Go to Step 5

4 | Test the sensor ground 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 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK