GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The mode actuator is an electronic device that incorporates a stepper motor and feedback potentiometer. The HVAC control module 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. As the actuator moves, the potentiometer produces the actual door position signal that is sent to the HVAC control module. The HVAC control module continues to command the actuator to move until the desired and actual values are equal. The door directs airflow through the outlets as selected by the vehicles occupants.

Conditions for Running the DTC

    • The ignition is ON.
    • Ignition voltage is between 9-16 volts.
    • An mode actuator positional change is attempted.

Conditions for Setting the DTC

The actual mode door position differs from the commanded mode door position by 4 counts or more.

Action Taken When the DTC Sets

The mode actuator is considered stalled and the HVAC control module will command the mode actuator to stop rotation (2.5 V).

Conditions for Clearing the DTC

    • If the HVAC control no longer detects a failure, then the DTC will become history.
    • The history DTC will clear after 50 ignition cycles without a failure.
    • The DTC can be cleared with a scan tool.

Diagnostic Aids

    • A dead zone exists in a range 10 counts above or below the mode door max or mode door min positions. When the mode door actual data parameter is within the dead zone, the DTC will not set. If the mode door commanded data parameter differs from the mode door actual data parameter by 4 counts or more outside the dead zone, the DTC will set.
    • A damaged or broken mode door and or actuator can cause this DTC to set.

Step

Action

Value(s)

Yes

No

Schematics Reference: HVAC Air Delivery/Temperature Control Schematics

1

Did you perform the HVAC Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check

2

  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, observe the Mode Door Commanded data parameter and the Mode Door Actual data parameter in the Primary ECC Data list.

Does the scan tool indicate that the Mode Door Commanded data parameter is within the specified value of the Mode Door Actual data parameter?

0-3  counts

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. With the scan tool, command the mode actuator from panel (ON) to defrost (OFF).
  2. With the scan tool, observe the mode actuator actual position.

Does the scan tool indicate that the mode actuator actual parameter changes within the specified range when it is commanded from panel to defrost?

5-250  counts

Go to diagnostic aids

Go to Step 4

4

Test the mode door actuator ignition 3 circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 5

5

Test the 5 volt reference circuit of the mode actuator for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 6

6

Test the mode door control circuit 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 13

Go to Step 7

7

Important: The air temperature actuator connector and the HVAC control module connector must be connected to correctly perform test.

  1. Turn on the ignition, with the engine off.
  2. With the scan tool, observe mode actuator actual parameter in the Primary ECC Data List.
  3. Connect a 3 amp fused jumper wire between the mode door control circuit of the mode actuator and the 5 volt reference circuit of the mode actuator (drives the door to panel).
  4. Remove the reconnect the jumper wire between the mode door control circuit of the mode actuator to ground circuit of the mode actuator (drives the door to defrost).

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

--

Go to Step 13

Go to Step 8

8

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

    • Incorrectly installed mode actuator.
    • Broken or binding linkages or mode door.
    • Obstruction that prevents the mode door from operating within it's full range of motion.

Did you find and correct the condition?

--

Go to Step 10

Go to Step 9

9

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 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 in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Replace the mode actuator. Refer to Mode Actuator Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

Important: Perform the recalibration procedure for the HVAC control module.

Replace the HVAC control module. Refer to Control Assembly Replacement .

Did you complete the replacement?

--

Go to Step 13

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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 2

System OK