For 1990-2009 cars

### 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

1. Ignition switch ON
2. Check the ignition voltage, 12 volt and motor voltage, 5 volt of air intake door motor.
3. 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 | Go to Diagnostic System Check - Vehicle
2 | Is DTC B3779 set as a current DTC? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | 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 |

1. Disconnect the fused jumper.
2. Measure the voltage between the 5-volt reference circuit and the low reference circuit of the HVAC door actuator.

Does the voltage measure less than the specified value?

5.5V

Go to Step 5

Go to Step 10

5 |

1. Turn OFF the ignition.
2. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection .
3. Measure the resistance from the low reference circuit of the HVAC door actuator to a good ground.

Does the resistance measure less than the specified value?

5 ohms

Go to Step 11

Go to Step 13

6 |

1. Disconnect the most accessible affected HVAC door actuator.
2. Probe the low reference circuit of the HVAC door actuator with a test lamp from battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 14

7 |

1. Turn ON the ignition, with the engine OFF.
2. With a scan tool, observe the Heating and Air Conditioning DTC list.
3. While observing the DTC list, disconnect and connect the electrical connector for each affected HVAC door actuator.

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 |

1. Disconnect the HVAC control module.
2. Test the low reference circuit of the appropriate HVAC door actuator for a high resistance or for an open.

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 |

1. Use the scan tool in order to clear the DTCs.
2. Operative the vehicle according to the Conditions for Running in the DTC as specified in the supporting text.

Does the DTC set again?

--

Go to Step 4

System OK