Circuit Description
The mode actuator is an electronic stepper motor. The HVAC control module (IPM) supplies power and ground to the actuator. The IPM controls the direction of the mode actuator by changing the polarity of the control circuits. When the actuator reaches its desired position, both circuits are fixed to the same value (9.5 to 12 volts). The IPM determines the door position by counting pulses (voltage fluctuations) caused by the brush to commutator action generated during normal motor operation. The IPM monitors a voltage drop across an internal resistance to detect the pulses. The IPM converts the pulses to counts with a range of 0 to 255 counts.
When a calibration or recalibration procedure is performed, the IPM calculates the mode door travel range. The IPM commands the actuator to each extreme position and counts the total number of pulses. The IPM 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.
Conditions for Running the DTC
The IPM will run the DTC when either of the following conditions are met.
| • | The IPM has completed a calibration/recalibration of the mode actuator. |
| • | The IPM commands the actuator to move. |
Conditions for Setting the DTC
The IPM will set this DTC if either of the following conditions are true.
| • | The mode actuator fails calibration/recalibration due to an over travel or under travel condition. (The IPM does not detect the calibrated number of total pulse counts during a travel range check.) |
| • | The IPM determines that the actual door position does not equal the commanded door position. (The IPM commands the door to move but does not see the expected number of pulses between positions.) |
Action Taken When the DTC Sets
| • | The IPM will attempt to make use of whatever range is still available. |
| • | The IPM will recalibrate the mode actuator each time the ignition switch is turned ON. |
Conditions for Clearing the MIL/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
| • | Inspect the mode door and mode actuator for the following conditions: |
| - | A misaligned mode actuator. Refer to Mode Actuator Replacement . |
| - | Broken or binding linkages or mode door |
| - | Obstruction that prevents the mode door from operating within its full range of motion |
| - | Missing seals to the mode door |
| - | Misaligned seals to the mode door |
| • | 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.
-
This step verifies that the IPM is able to command the mode actuator through its full range of motion.
-
This step verifies that the IPM has successfully calibrated the mode actuator.
-
If the actuator does not move at all, the problem is likely to be the drive circuitry within the IPM, 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 mode door or mode door linkage.
-
This step drives the actuator to the vent position. The mode actuator will not move if the mode door is in already at the extreme position.
-
This step drives the actuator to the defrost position.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | |
Does the scan tool indicate that the value of the Htr./Def./A/C Dr. Actual parameter changes from the minimum specified value to the maximum specified value? | 0 Counts 255 Counts | Go to Step 3 | Go to Step 4 | |
With a scan tool observe the Htr./Def./A/C Dr. Cal. Status parameter in the Instrument Panel Module data list. Does the scan tool display Cal OK? | -- | Go to Diagnostic Aids | Go to Step 8 | |
Does the scan tool indicate that the value of the Htr./Def./A/C Dr. Actual parameter changes by more than the specified value? | 0-3 Counts | Go to Step 8 | Go to Step 5 | |
5 | Test the mode door control A circuit and the mode door control B circuit for an open, high resistance, short to ground or a 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 6 |
Does the mode actuator shaft rotate? | -- | Go to Step 10 | Go to Step 7 | |
Does the mode actuator shaft rotate? | -- | Go to Step 10 | Go to Step 8 | |
8 | Inspect the mode door and mode actuator for the following conditions:
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 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 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 13 | Go to Step 12 |
11 |
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 13 | -- |
12 |
Important: Perform the recalibration procedure for the IPM. Replace the IPM. Refer to HVAC Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Does the DTC reset? | -- | Go to Step 3 | System OK |
