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. This input is processed by the controller and sent to the Body Control Module (BCM) where it is pulled up to a 12 volt pull-up resistor.
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 the DTC is a history or intermittent. Try performing the tests shown while moving the wiring harnesses and connectors, this can often cause the malfunction to appear. |
| • | Visually inspect sensor connector and harness for damage, corrosion or water intrusion. |
| • | Check for adequate terminal tension, mis-routed harness, rubbed through wire insulation, and broken wire(s) inside the insulation. |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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This step checks for available reference voltage from the heater and A/C control. A normal reading should be approximately 5.0 - 5.5 V. A significantly higher voltage reading indicates a circuit problem.
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This step isolates the circuit and a check is made for a short to battery.
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This step rechecks the circuit for a short to battery but with the ignition switch ON.
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If no apparent circuit problem was found in the previous steps and the DTC resets, the most likely cause is a heater and A/C control malfunction.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Air Delivery System Check performed? | -- | ||
Is the voltage reading within the specified value? | 5.0-5.5 V | Go to Diagnostic Aids | ||
Is the voltage reading within the specified value? | Less than 0.1 V | |||
Is the voltage reading within the specified value? | Less than 0.1 V | |||
5 | Locate and repair the short to B+ on CKT X812. Is the repair complete? | -- | -- | |
Is a current DTC 39 present? | -- | System OK | ||
7 | Replace and program the heater and A/C control. Refer to Control Assembly Replacement for the programming procedure. Is the replacement and programming complete? | -- | -- |
