B2646

DTC B2646

Circuit Description
The HVAC control module determines the ambient light conditions either Daylight or Low Light based on the voltage from the ambient light sensor. The HVAC control module provides the ambient light sensor with a low reference circuit and a ambient light sensor signal circuit. The HVAC control module then sends out a class 2 message to the body control module (BCM) indicating the outside light condition base on the signal from the ambient light sensor. When the ambient light sensor detects Low Light or Daylight conditions, a varying voltage is applied to the HVAC control module through the ambient light sensor signal.

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 Low Light.

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.