Circuit Description
The HVAC control module receives a left air temperature actuator position signal from the left air temperature actuator. The left air temperature actuator position sensor is a potentiometer that is tied to a 5 volt reference source. The variable output from the potentiometer feeds back a position signal to a pull-up resistor located in the HVAC control module. This signal is used to determine the necessary drive signal to the left air temperature actuator motor to provide the proper air mix door position. This value is stored in the Keep Alive Memory (KAM) portion of the HVAC control module.
When the HVAC control module is first connected to power (or the battery connection is established), the system will perform an initialization routine lasting approximately 60 seconds. During this routine, both right and left air temperature actuators will cycle full travel in both directions learning the end positions. Position feedback readings are sent back to the HVAC control module and compared to a range of acceptable end readings. If during initialization the position feedback readings are not within the acceptable range, a diagnostic code will be set. If the position feedback readings reach values of 0-5 counts or 250-255 counts, the HVAC control module will then interpret the reading as a "feedback-short" or "feedback-open" condition respectively.
Important: Feedback-short or feedback-open conditions can occur due to air temperature actuators being initialized while not being attached to the HVAC module case.
Conditions for Running DTC
The ignition is in the ON position.
Conditions for Setting the DTC
| • | A damaged or bound up temperature door mechanism. |
| • | Improper alignment of the temperature door after air temperature actuator replacement. |
| • | The air temperature actuator has not been initialized after replacement. |
| • | During initialization, the position feedback reading is not within an acceptable range. |
Action Taken When the DTC Sets
No driver warning message will be displayed for this DTC.
Conditions for Clearing the DTC
| • | The DTC will become history if the HVAC control module 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
Install a scan tool to the diagnostic link connector. Turn the ignition switch to the ON position. Select the OUTPUT CONTROL screen in HVAC special functions. Use the MISCELLANEOUS TEST screen to manually drive the left air temperature actuator with the scan tool from fully open to fully closed. Monitor the LH MIX MTR POSITION FEE with the scan tool when this is done. A normal position feedback signal should range between 0-255 counts as the electric actuator is being moved.
If condition not present refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
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Tests for the proper operation of the circuit in the high voltage range.
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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.
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Tests for a short to ground in the 5 volt reference circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the LH Mix Mtr Position Fee parameter is within the specified range? | 5-250 Counts | Go to Diagnostic Aids | Go to Step 3 |
Does the scan tool indicate that the LH Mix Mtr Position Fee parameter is greater than the specified value? | 250 Counts | Go to Step 4 | Go to Step 8 | |
Does the scan tool indicate that the LH Mix Mtr Position Fee parameter is less than the specified value? | 5 Counts | Go to Step 5 | Go to Step 9 | |
Does the scan tool indicate that the LH Mix Mtr Position Fee parameter is greater than the specified value? | 250 Counts | Go to Step 7 | Go to Step 6 | |
6 | Test the 5-volt reference circuit of the left air temperature 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 15 | Go to Step 12 |
7 | Test the 5 volt reference circuit of the left air temperature actuator for an open, high resistance or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 11 |
8 | Test the signal circuit of the left air temperature 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 15 | Go to Step 12 |
9 | Test the signal circuit of the left air temperature 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 15 | Go to Step 10 |
10 | Test the low reference circuit of the left air temperature 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 15 | Go to Step 12 |
11 | Inspect for poor connections at the harness connector of the left air temperature 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 15 | Go to Step 13 |
12 | 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 15 | Go to Step 14 |
13 | Replace the left air temperature actuator. Refer to Air Temperature Actuator Replacement - Left Side . Did you complete the replacement? | -- | Go to Step 15 | -- |
14 | Replace the HVAC control module. Refer to HVAC Control Module Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- |
15 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
