GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Park Avenue 🢒 Restraints 🢒 SIR 🢒 DTC B1340, B1341, B1343, or B1344

Circuit Description

The instrument panel module (IPM) controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5, or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts. The IPM converts the voltage values to count values where one volt is approximately equal to 51 counts. The IPM uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC B1340 Left Air Temperature Actuator
    • DTC B1341 Right Air Temperature Actuator
    • DTC B1343 Recirculation Actuator
    • DTC B1344 Mode Actuator

Conditions for Running the DTC
    • The ignition is turned ON.
    • The IPMs keep alive memory (KAM) battery power must be interrupted to run the range check. This can be accomplished with the scan tool by commanding HVAC Recalibration in Heating and Air Conditioning Special Functions.

Conditions for Setting the DTC
    • Left air temperature actuator
       - The IPM detects the position signal circuit is less than 0.25 volt (13 counts) or more than 4.08 volts (208 counts).
       - The actuators total travel range, max-min is less than or more than the calibrated limits.
    • Right air temperature actuator
       - The IPM detects the position signal circuit is less than 0.88 volt (45 counts) or more than 4.35 volts (222 counts).
       - The actuators total travel range, max-min is less than or more than the calibrated limits.
    • Mode actuator
        The actuators total travel range, max-min is less than or more than the calibrated limits.
    • Recirculation actuator
       - The IPM detects the position signal circuit is less than 0.25 volt (13 counts) or more than 4.80 volts (245 counts).
       - The actuators total travel range, max-min is less than or more than the calibrated limits.

Action Taken When the DTC Sets
    • A default value will be substituted for the door position data by the IPM.
    • Each time the ignition switch is turned ON, the IPM will recheck the actuator travel range.
    • The IPM will continue to make use of whatever travel range is still available.

Conditions for Clearing the DTC
    • The DTC will become history if the IPM no longer detects a failure.
    • The history DTC will clear after 50 fault-free ignition cycles.
    • The DTC can be cleared with a scan tool.

Diagnostic Aids
    • If the condition is not present refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • The range fault can only be detected following a check of the actuator travel range. The actuator travel range check can only be initiated by disrupting power to the IPM.
    • An actual range below this limit suggest an obstruction or something stuck in the door limiting travel. An actual range above this limit suggests an over travel condition such as damaged or missing foam seal.
    • A damaged or broken door an or actuator can cause the DTC to set by allowing the actuator shaft to rotate unrestricted to its internal stop. The internal stops are outside of the working range of the feedback potentiometers 0-250 counts.
    • Left air temperature actuator--The calibration limit is 152-250 counts.
    • Right air temperature actuator--The calibration limit is 130-250 counts.
    • Recirculation actuator--The calibration limit is 165-195 counts.
    • Mode actuator--The calibration limit is 215-245 counts.

Test Description

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

  1. Tests for the HVAC actuator operating within its travel range.

    2.

  2. Test the actual travel range of the HVAC actuator.

    3.

  3. Tests the HVAC actuator for proper operation.

    4.

  4. Tests for the proper operation of the circuit in the high voltage range.

    5.

  5. Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

    6.

  6. Tests for a short in the 5-volt reference circuit.

    7.

  7. Tests the HVAC actuator door position signal circuit for a short to ground.

    8.

  8. Tests the HVAC actuator door position signal circuit for a short to voltage, high resistance, or an open.

    9.

  9. Tests the HVAC actuator low reference circuit for high resistance or an open.

    10.

  10. Tests the HVAC actuator ignition 3 voltage circuit for high resistance or an open.

    11.

  11. Tests the HVAC actuator door control circuit for an open, high resistance, or a short to ground.

    12.

  12. Test for an inoperative HVAC actuator.

    13.

  13. Tests for proper operation of the IPM.

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 in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the appropriate Dr. Actual parameter in the Heating and Air Conditioning HVAC Door Positions data list.

Does the scan tool indicate that the Dr. Actual parameter is within the specified range?
    • Left Air Temperature Actuator: 0.25-4.16 V
    • Right Air Temperature Actuator: 0.71-4.41 V
    • Recirculation Actuator: 0.25-4.75 V
    • Mode Actuator: 0.06-4.84 V

Go to Step 3

Go to Step 4

3

  1. With the scan tool, observe the appropriate Min Dr. Pos data parameter and the Max Dr. Pos data parameter in the Heating and Air Conditioning HVAC Door Calibrations data list.
  2. Subtract the Min Dr. Pos from the Max Dr. Pos.

Does the result of the calculation indicate that the actual travel of the actuator is within the specified range?

    • Left Air Temperature Actuator: 152-250 Counts
    • Right Air Temperature Actuator: 130-250 Counts
    • Recirculation Actuator: 165-195 Counts
    • Mode Actuator: 165-195 Counts

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 14

4

  1. With a scan tool, command the appropriate actuator:
    2. • Left Temp Door Position from Hot to Cold
    • Right Temp Door Position form Hot to Cold
    • Air Inlet from Recirc. to Outside
    • Htr./Det./A/C from Defrost to A/C
  2. With a scan tool, observe the appropriate Dr. Actual parameter.

Does the scan tool indicate that the appropriate Dr. Actual parameter changes when the appropriate Door Position is commanded?

--

Go to Step 5

Go to Step 6

5

Inspect the appropriate HVAC door for a condition allowing excessive travel of the actuator.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Disconnect the appropriate HVAC actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the appropriate Dr. Actual parameter.

Does the scan tool indicate that the Dr. Actual parameter is more than the specified value?
    • Left Air Temperature Actuator: 4.08 V
    • Right Air Temperature Actuator: 4.35 V
    • Recirculation Actuator: 4.75 V
    • Mode Actuator: 4.75 V

Go to Step 7

Go to Step 11

7

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the door position signal circuit and the low reference circuit of the appropriate HVAC actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the appropriate Dr. Actual parameter.

Does the scan tool indicate that the Dr. Actual parameter is less than the specified value?
    • Left Air Temperature Actuator: 0.25 V
    • Right Air Temperature Actuator: 0.88 V
    • Recirculation Actuator: 0.25 V
    • Mode Actuator: 0.25 V

Go to Step 8

Go to Step 12

8

  1. Turn OFF the ignition.
  2. Disconnect the fused jumper wire.
  3. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the door position signal circuit of the appropriate HVAC actuator.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the appropriate Dr. Actual parameter.

Does the scan tool indicate that the Dr. Actual parameter is more than the specified value?
    • Left Air Temperature Actuator: 4.08 V
    • Right Air Temperature Actuator: 4.35 V
    • Recirculation Actuator: 4.75 V
    • Mode Actuator: 4.75 V

Go to Step 10

Go to Step 9

9

Test the 5-volt reference circuit of the appropriate HVAC actuator for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 12

10

Test the 5-volt reference circuit for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 11

11

Test the door position signal circuit of the appropriate HVAC actuator for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 12

12

Test the door position signal circuit of the appropriate HVAC actuator for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 13

13

Test the low reference circuit of the appropriate HVAC actuator for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 20

14

Test the ignition 3 voltage circuit of the appropriate HVAC actuator for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 15

15

Test the door control circuit of the appropriate HVAC actuator for an open, high resistance, short to ground or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 16

16

Important: Ensure that the appropriate HVAC actuator connector and the instrument panel module (IPM) connector are connected during this step in order to avoid misdiagnosis.

  1. Turn ON the ignition, with the engine OFF.
  2. With the scan tool, observe the appropriate Dr. Actual data parameter in the Heating and Air Conditioning HVAC Door Positions data list.
  3. Connect a 3-amp fused jumper wire between the door control circuit and the 5-volt reference circuit of the appropriate HVAC actuator.
  4. Remove and reconnect the jumper wire between the door control circuit and the low reference circuit of the appropriate actuator.

Does the actuator drive shaft rotate and do the counts change?

--

Go to Step 17

Go to Step 19

17

  1. Measure the voltage from the door control circuit of the appropriate HVAC actuator and a good ground.
  2. With a scan tool, command the appropriate actuator:
    3. • Left Temp Door Position from Hot to Cold
    • Right Temp Door Position form Hot to Cold
    • Air Inlet from Recirc. to Outside
    • Htr./Det./A/C from Defrost to A/C

Does the voltage measure near the specified value for each commanded state?

0 V

5 V

2.5 V stationary

Go to Step 18

Go to Step 20

18

Inspect the appropriate HVAC door and the actuator for the following conditions:

    • A misaligned HVAC door actuator--Refer to the appropriate replacement procedure:
       -  Mode Actuator Replacement
    • Broken or binding linkages
    • A broken or a binding HVAC door
    • Any obstruction that prevents the HVAC door from operating within it's full range of motion
    • Missing seals to the HVAC door
    • Misaligned seals to the HVAC door

Did you find and correct the condition?

--

Go to Step 23

Go to Diagnostic Aids

19

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

Did you find and correct the condition?

--

Go to Step 23

Go to Step 21

20

Inspect for poor connections at the harness connector of the IPM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 23

Go to Step 22

21

Important: : Perform the recalibration procedure for the HVAC door actuators.

Replace the HVAC door actuator. Refer to the appropriate replacement procedure:

Did you complete the replacement?

--

Go to Step 23

--

22

Replace the IPM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 23

--

23
  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 2

System OK