B0408

CIRCUIT DESCRIPTION
The air temperature actuator is an electronic device that incorporates a stepper motor and a feedback potentiometer. The HVAC control module determines the position of the air temperature actuator from the voltage on the potentiometer. When the air temperature changes by greater than 4 counts, the control module performs the following functions:
- Drives the air temperature actuator in the appropriate direction in order to achieve the desired setting
- Compares the actual position to the commanded position

If the actual value differs from the commanded value by 4 or more counts, the actuator is stalled, and the DTC will set.

CONDITIONS FOR RUNNING THE DTC
- The ignition is ON.
- Ignition voltage is between 9-16 volts.
- An actuator change in position is attempted.

CONDITIONS FOR SETTING THE DTC
The actual position of the air mix door differs from the commanded position by at least 4 counts.

ACTION TAKEN WHEN THE DTC SETS
The actuator is stalled, and the HVAC control module will command the actuator to stop rotation.

CONDITIONS FOR CLEARING THE DTC
- If the HVAC control no longer detects a condition, then the DTC will become history.
- The history DTC will clear after 50 ignition cycles without a condition.
- The DTC can be cleared with a scan tool.

DIAGNOSTIC AIDS
- A dead zone exists in a range 10 counts above the mix door maximum position to 10 counts below the mix door minimum position. When the air mix door actual data parameter is within the dead zone, the DTC will not set. If the commanded data parameter differs from the actual data parameter by 4 or more counts outside the dead zone, the DTC will set.
- A damaged air temperature door, a damaged actuator, a broken air temperature door, or a broken actuator can cause this DTC to set.
- If the condition is not present, refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST DESCRIPTION

Steps 1-8:

Steps 9-15:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the air temperature door position is within the specified range of the commanded value.
4. Tests for the proper operation of the circuit in the low voltage range.
5. Tests for the proper operation of the circuit in the high voltage range. If the jumper fuse opens when you perform this test, then the signal circuit contains a short to ground.
6. Tests for a short to voltage in the 5-volt reference circuit.