GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The actuators are a 2-wire bi-directional electric motor. Two control circuits enable the actuators to operate. The control circuits use either a 0 or 12-volt value to coordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds the appropriate control circuit for the commanded direction. The HVAC control module reverses the polarity of the control circuits to move the actuators in the opposite direction. The HVAC control module determines the door position by counting motor pulses on one of the control circuits. These pulses are small voltage fluctuations that occur when the brush is shorted across 2 commutator contacts as the motor rotates. As the actuator shaft rotates, the HVAC control module monitors the voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position.

When a calibration or recalibration procedure is performed, the HVAC control module calculates the door travel range. The HVAC control module commands the actuator to each extreme position and counts the total number of pulses. The HVAC control module compares the total number of pulses to calibrated limits. If the total pulse count is less than or equal to the maximum calibrated limit and greater than or equal to the minimum calibrated limit, then the calibration is considered successful.

    • Temperature control 1 circuit refers to the air temperature actuator.
    • Air flow control 3 circuit refers to the mode actuator.
    • Air flow control 7 circuit refers to the recirculation actuator.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC B0248 Air Flow Control 3 Circuit
    • DTC B0268 Air Flow Control 7 Circuit
    • DTC B0408 Temperature Control 1 Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

DTC Symptom

DTC Symptom Descriptor

05

Short to Battery or Open Circuit

06

Short to Ground or Open

4B

Calibration not Learned

51

Calibration Failure

61

Actuator Stuck

11

Above Maximum Threshold

12

Below Minimum Threshold

Conditions for Running the DTC

    • The ignition is turned ON.
    • The ignition voltage is between 9-16 volts.

Conditions for Setting the DTC

2A and 61

Sets after 2 occurrences of the test fail code setting conditions listed below in the same ignition cycle.

51 and 04

Sets after one occurrence of the test fail code setting conditions listed below in the same ignition cycle.

2A, 04, 51 and 61

The following failures occur and set the DTC:

    • The HVAC control module does not detect any movement of the actuator.
    • The HVAC control module detects a measured actuator range that exceeds the calibratible value.
    • The HVAC control module detects a measured actuator range that is less than the calibratible value.
    • The HVAC control module detects a calibratible procedure time that exceeds the calibratible value.
    • The HVAC control module detects the actuator motor as stalled before the actuator motor reaches the expected stall at the end of the travel. When the drive voltage is reversed, the motor is unable to move more than a calibratible amount in the other direction.
    • The HVAC control module detects the actuator motor as stalled before the actuator motor reaches the expected stall at the end of the travel. But, when the drive voltage is reversed, the motor is able to move more than a calibratible amount in the other direction.

Action Taken When the DTC Sets

2A

The HVAC control module will use a default range to retry calibration procedure when the ignition is OFF.

61

The HVAC control module will stop trying to move the air temperature actuator motor during the current ignition cycle.

04

The HVAC control module will retry the command to move the actuator in a certain direction in 5-minute intervals.

51

The HVAC control module will retry calibration when the ignition is OFF.

Conditions for Clearing the MIL/DTC

    • The DTC will become history if the HVAC control module no longer detects a failure.
    • The history DTC will clear after 40 fault-free ignition cycles.
    • The DTC can be cleared with a scan tool.

Diagnostic Aids

    • Inspect the actuator door and actuator for the following conditions:
       - A misaligned air temperature actuator--Refer to Temperature Valve Actuator Replacement .
       - Broken or binding linkages or actuator door
       - Obstruction that prevents the actuator door from operating within its full range of motion
       - Missing seals to the actuator door
       - Misaligned seals to the actuator door
    • Refer to Testing for Intermittent Conditions and Poor Connections .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step verifies that the HVAC control module is able to command the appropriate actuator through its full range of motion.

  2. This step verifies the position of the actuators.

  3. If the actuator does not move at all, the problem is likely to be the drive circuitry within the HVAC control module, the actuator, or the wiring harness. If the actuator does move, but not within its full range of motion, the problem is likely to be a mechanical binding of the actuator door or actuator door linkage.

  4. This step drives the actuator in one position. The actuator shaft will not move if the actuator door is already in the position you are attempting to drive it to.

  5. This step drives the actuator in the opposite direction.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, command the actuators in both directions.
  4. Observe the Temp, Mode and Recirc Door Position parameter.

Does the scan tool indicate that the value of the Door parameter changes from the minimum specified value to the maximum specified value?

0 Counts

255 Counts

Go to Step 3

Go to Step 4

3

With a scan tool, recheck the Actuator Position parameter in the HVAC control module data list.

Does the scan tool display correct values?

--

Go to Diagnostic Aids

Go to Step 8

4

Does the scan tool indicate that the value of the appropriate Door Position parameter changes by more than the specified value?

0-3 Counts

Go to Step 8

Go to Step 5

5

Test the door control A circuit and the door control B circuit for the following:

    • An open
    • A high resistance
    • A short to ground
    • A short to voltage

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Disconnect the HVAC control module.
  3. Connect a 10-amp fused jumper wire between the door control A circuit of the appropriate actuator and battery positive voltage.
  4. Connect a 10-amp fused jumper wire between the door control B circuit of the appropriate actuator and a good ground.

Does the actuator shaft rotate?

--

Go to Step 10

Go to Step 7

7

  1. Connect a 10-amp fused jumper wire between the door control B circuit of the appropriate actuator and battery positive voltage.
  2. Connect a 10-amp fused jumper wire between the door control A circuit of the appropriate actuator and a good ground.

Does the actuator shaft rotate?

--

Go to Step 10

Go to Step 8

8

Inspect the appropriate air temperature, recirc door, or mode door actuator for the following conditions:

    • A misaligned actuator.
    • Broken or binding linkages or actuator door
    • An obstruction that prevents the actuator door from operating within its full range of motion
    • Missing seals to the actuator door
    • Misaligned seals to the actuator door

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

9

Inspect for poor connections at the harness connector of the appropriate actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

10

Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Important: Perform the recalibration procedure for the appropriate actuator after the replacement. Upon fuse replacement, a recalibration of the actuator will occur.

Replace the appropriate actuator.

    • Air temperature actuator--Refer to Temperature Valve Actuator Replacement .
    • Mode actuator--Refer to Mode Actuator Replacement .
        
    • Recirculation actuator--Refer to Recirculation Actuator Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

Replace the HVAC control module. Refer to Control Module References for HVAC replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 13

--

13

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

Does the DTC reset?

--

Go to Step 3

System OK