GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2001 🢒 LeSabre 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B0252

Circuit Description

The mode actuator is an electronic stepper motor with a feedback potentiometer. The instrument panel integration module (IPM) determines the position of the mode door based on the voltage from the potentiometer. When the airflow is from the panel, the voltage is high. When the airflow is from the defrost outlet, the voltage is low. The IPM controls the mode door position to direct airflow from the outlets selected by the vehicle occupants.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The IPM detects the mode door position signal is less than 5 counts (0.1 volts) or greater than 250 counts (4.9 volts).

Action Taken When the DTC Sets
    • The IPM will only direct airflow from either the vent or defrost outlets.
    • If B0252 sets during a calibration/recalibration event, the IPM will no longer issue commands to the actuator and will not perform a calibration/recalibration until the door position feedback fault is corrected.

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
    • A disconnected or broken door/linkage may also set this DTC during calibration/recalibration by allowing the actuator to travel to its minimum internal stop (over travel condition).
    • If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

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

    2.

  2. 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.

    3.

  3. Tests for a short to ground in the 5 volt reference circuit.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

1

Did you perform the HVAC Diagnostic System Check?

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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 Htr./Def./A/C Dr. Actual parameter in the Instrument Panel Module data list.

Does the scan tool indicate that the Htr./Def./A/C Dr Actual parameter is within the specified range?

13-250 counts

(0.25-4.9 V)

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the mode actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Htr./Def./A/C Dr. Actual parameter.

Does the scan tool indicate that the Htr./Def./A/C Dr Actual parameter is greater than the specified value?

250 counts

(4.9 V)

Go to Step 4

Go to Step 8

4

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

Does the scan tool indicate that the Htr./Def./A/C Dr. Actual parameter is less than the specified value?

13 counts (0.25 V)

Go to Step 5

Go to Step 9

5

  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 of the mode actuator and the mode door position signal circuit of the mode actuator.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the Htr./Def./A/C Dr. Actual parameter.

Does the scan tool indicate that the Htr./Def./A/C Dr. Actual parameter is greater than the specified value?

250 counts (4.9 V)

Go to Step 7

Go to Step 6

6

Test the 5 volt reference circuit of the mode 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 16

Go to Step 13

7

Test the 5 volt reference circuit of the mode 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 16

Go to Step 11

8

Test the mode door position signal circuit of the mode 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 16

Go to Step 15

9

Test the mode door position signal circuit of the mode 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 16

Go to Step 10

10

Test the low reference circuit of the mode 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 16

Go to Step 13

11

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

  1. A misaligned mode actuator. Refer to Mode Actuator Replacement .
  2. Broken or binding linkages or mode door
  3. An obstruction that prevents the mode door from operating within it's full range of motion
  4. Missing seals to the mode door
  5. Misaligned seals to the mode door

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

12

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

13

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 16

Go to Step 15

14

Important: Recalibrate the mode actuator.

Replace the mode actuator. Refer to Mode Actuator Replacement .

Did you complete the replacement?

--

Go to Step 16

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15

Important: Recalibrate the IPM.

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

Did you complete the replacement?

--

Go to Step 16

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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