B2646

DTC B2646

CIRCUIT DESCRIPTION
The HVAC Control Module determines the ambient light conditions either DAYTIME or NIGHT based on the voltage from the ambient light sensor. The HVAC control module provides the ambient light sensor with a 5 volt reference voltage and a signal return circuit. The ambient light sensor signal circuit is a direct input to the HVAC control module. The HVAC control module sends out a class 2 message to the dash integration module (DIM) indicating the outside light condition base on the signal from the ambient light sensor.

CONDITIONS FOR RUNNING THE DTC
This test is run every 250 milliseconds.

CONDITIONS FOR SETTING THE DTC
The twilight sensor voltage is less than 0.09 V or greater than 4.75 V on 3 consecutive tests.

ACTION TAKEN WHEN THE DTC SETS
Twilight status set to "NIGHT".

CONDITIONS FOR CLEARING THE MIL/DTC
The HVAC control module does not detect a voltage that is less than or greater than the predetermined value during the diagnostic self test.

DIAGNOSTIC AIDS
- The following may cause an intermittent:
- Bent terminal
- Backed out terminal
- Damaged terminal
- Poor terminal tension
- Chafed wire
- Broken wire inside the insulation
- When diagnosing for an intermittent short or an open, manipulate the wire harness while watching the test equipment for changes.

TEST DESCRIPTION

Steps 1-2:

Steps 3-6:

Steps 7-12:

Steps 13-14:

The numbers below refer to the step numbers on the diagnostic table.
3. Tests for the proper operation of the circuit in the low voltage range.
4. Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.
5. Tests for a short to voltage in the 5 volt reference circuit.