GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2002 🢒 LeSabre 🢒 DTC 🢒 DTC B0249

Circuit Description

The mode actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The instrument panel integration module (IPM) controls the mode door position by sending a control signal to the actuator. The signal's value is dependent upon the desired mode selected by the vehicle occupants. The control signal is near 0 V when the mode actuator is commanded toward the defrost position, near 5 V when commanded toward the vent position, and near 2.5 V when stationary. As the mode actuator moves, the potentiometer produces the actual door position signal that is sent to the IPM. The IPM continues to command the actuator to move until the desired and actual values are equal.

When a calibration or recalibration procedure is performed, the IPM calculates the mode door travel range. The IPM commands the actuator through it's full range. The IPM stores the learned minimum and maximum position values. The travel range value is calculated by subtracting the minimum position value from the maximum position value. The IPM compares the travel range to calibrated limits. If the travel range value 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. The IPM continuously compares the actual actuator position to the calibrated minimum and maximum position values.

Conditions for Running the DTC
    • The range fault code can only be set following a calibration/recalibration of the mode actuator.
    • The IPM will not perform a calibration/recalibration of the mode actuator if DTC B0252 is set as current.

Conditions for Setting the DTC

The actual total travel range of the mode door (max - min) is less than 200 counts or greater than 246 counts.

Action Taken When the DTC Sets
    • The IPM will continue to make use of whatever travel range is still available.
    • The IPM will recalibrate the mode door travel range each time the ignition switch is turned ON.

Conditions for Clearing the DTC
    • A successful recalibration of the mode door must be completed.
    • A history DTC will clear after 50 fault-free ignition cycles.
    • Use the scan tool in order to clear the DTCs.

Diagnostic Aids
    • If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • The calibration limit is 200-246 counts (3.9-4.8 V). An actual range below this limit suggests an obstruction of the mode door or a binding linkage limiting travel. An actual range above this limit suggests an over travel condition (damaged or missing foam seals).

Test Description

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

  1. A total travel range greater than 15 counts indicates a mechanical malfunction with the door or linkage, causing an over travel or under travel condition. A total travel range less than 15 counts indicates an electrical malfunction, binding door, or binding linkage.

  1. This step uses the fused jumper wire to drive the actuator to its maximum and minimum positions. Use the scan tool to determine the total travel range of the actuator (maximum position - minimum position).

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

1

Did you perform the HVAC Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2
  1. Install a scan tool
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Min. Htr./Def./A/C Dr. Pos and Max. Htr./Def./A/C Dr. Pos parameters in the Instrument Panel Module data list.
  4. Subtract the value of the Min Htr./Def./A/C Dr. Pos parameter from the value of the Max Htr./Def./A/C Dr. Pos parameter.

Does the result of the calculation indicate that the travel range of the mode door is within the specified range?

200-246 Counts

(3.9-4.8 V)

Go to Diagnostic Aids

Go to Step 3

3

Does the result of the calculation indicate that the travel range of the mode door is greater than the specified value?

15 Counts

(0.3 V)

Go to Step 10

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the mode actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 3 voltage circuit of the mode actuator with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 13

5

Measure the voltage from the 5 volt reference circuit of the mode actuator to a good ground.

Does the voltage measure near the specified value?

5 V

Go to Step 6

Go to Step 9

6

Important: The ignition must be cycled from OFF to ON with the mode actuator disconnected during this step. Failure to do this may result in misdiagnosis.

  1. Turn OFF the ignition.
  2. Turn ON the ignition, with the engine OFF.
  3. Measure the voltage from the mode door control circuit to a good ground.

Does the voltage measure near the specified value?

2.3-2.7 V

Go to Step 8

Go to Step 7

7

Test the mode door control circuit of the mode actuator for an open, 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 16

Go to Step 12

8

Important: Ensure that the mode actuator connector and the instrument panel integration module connector are connected during this step in order to avoid misdiagnosis.

  1. Turn the ignition OFF.
  2. Connect the mode actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. With the scan tool, observe the Htr./Def./A/C Dr Actual parameter in the Instrument Panel Module HVAC Door Positions data list.
  5. Connect a 3-amp fused jumper wire between the mode door control circuit and the 5 volt reference circuit of the mode actuator, driving the actuator toward the vent position.
  6. Remove and reconnect the jumper wire between the mode door control circuit and the low reference circuit of the mode actuator, driving the actuator toward the defrost position.

Does the scan tool indicate that the total travel range of the mode door is greater than the specified value?

15 Counts

Go to Step 12

Go to Step 10

9

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

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

10

Inspect the mode door and the mode actuator for the following conditions:

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

Did you find and correct the condition?

--

Go to Step 16

Go to Step 11

11

Inspect for poor connections at the harness connector of the mode 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 16

Go to Step 14

12

Inspect for poor connections at the harness connector of the instrument panel integration module (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 16

Go to Step 15

13

Repair the ignition 3 voltage circuit for an open. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 16

--

14

Important: Perform the Recalibration procedure for the mode actuator.

Replace the mode actuator. Refer to Mode Actuator Replacement .

Did you complete the replacement?

--

Go to Step 16

--

15

Important: Perform the Recalibration procedure for the IPM.

Replace the IPM. Refer to Instrument Panel Module Replacement in Body Control System.

Did you complete the replacement?

--

Go to Step 16

--

16
  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