Circuit Description
The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The module supplies a 5-volt source voltage to the potentiometer on the 5-volt reference circuit. The module supplies ground to the potentiometer through the low reference circuit. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The HVAC control module calibrates the travel range of the HVAC door actuators when it is initially powered by the battery positive voltage circuit. During calibration, the module commands the actuators in each direction until door travel is stopped. The module stores the minimum door positions and the maximum door positions of each actuator into memory. The total travel range is calculated by subtracting the minimum door position from the maximum door position. The door actuators can be calibrated again with a scan tool.
DTC Descriptors
This diagnostic procedure supports the following DTC :
DTC B3779 Mode Door Motor Feedback
Conditions for Running the DTC
Ignition is ON.
Conditions for Setting the DTC
The DTC sets when one of the following conditions are present:
| • | The mode door motor feedback voltage is less than 0.20 V. |
| • | The mode door motor feedback voltage is greater than 4.8 V. |
| • | The mode door motor position value is unattainable position. |
Conditions for Clearing the DTC
| • | The DTC will become history if the HVAC control module no longer detects a fault. |
| • | Ignition is ON or OFF. |
| • | The DTC can be cleared with a scan tool. |
Diagnostic Aids
- Ignition switch ON
- Check the ignition voltage, 12 volt and motor voltage, 5 volt of air intake door motor.
- Check the reference of air intake door motor.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 | Is DTC B3779 set as a current DTC? | -- | Go to Step 3 | |
3 | With a scan tool, observe the Heating and Cooling DTC list. Does the scan tool indicate that at least two of the following DTCs B0228 and B0413 are set as current DTC? | -- | Go to Step 6 | Go to Step 4 |
4 |
Does the voltage measure less than the specified value? | 5.5V | Go to Step 5 | Go to Step 10 |
5 |
Does the resistance measure less than the specified value? | 5 ohms | Go to Step 11 | Go to Step 13 |
6 |
Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 14 |
7 |
Did the scan tool indicate that only one DTC was present when a HVAC door actuator was disconnected? | -- | Go to Step 9 | Go to Step 8 |
8 | Test the 5-volt reference circuit of the appropriate HVAC door actuator for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
9 | Test the appropriate door position signal circuit of the HVAC door actuator for a short to ground. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 15 |
10 | Test the 5-volt reference circuit of the appropriate HVAC door actuator for a short to voltage. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
11 | Test the 5-volt reference circuit of the appropriate HVAC door actuator for a short to ground, for a high resistance, or for an open. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 12 |
12 | Test the 5-volt reference circuit of the appropriate HVAC door actuator for a short to ground, for a high resistance, or for an open. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
13 | Test the 5-volt reference circuit of the appropriate HVAC door actuator for a short to voltage. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
14 |
Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
15 | Inspect for poor connections at the harness connector of the appropriate HVAC door actuator. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 17 |
16 | Inspect for poor connections at the harness connector of the HVAC control module. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 18 |
17 |
Important: Perform the calibration procedure for HVAC door actuators. Replace the HVAC door actuator. Did you complete the replacement? | -- | Go to Step 19 | -- |
18 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 4 | -- |
19 |
Does the DTC set again? | -- | Go to Step 4 | System OK |
