Circuit Description
| • | DTC B0424 Air Temperature actuator performance |
| • | DTC B3748 Mode actuator performance |
| • | DTC B3749 Recirculation actuator performance |
The HVAC control module controls the HVAC actuators to regulate the airflow through the HVAC system. Each actuator is a 2 wire bi-directional electric motor. Two control circuits enable the actuator to operate. The control circuits use either a 0 or 12 volt value to co-ordinate the actuator movement. When the actuator is at rest, both control circuits have a value of 0 volts. In order to move the actuator, the HVAC control module grounds the appropriate control circuit for the commanded direction. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.
The HVAC control module determines the door position by counting motor pulses on one of the control circuits. The HVAC control module converts the pulses to counts with a range of 0-255 counts.
When a calibration or recalibration procedure is performed, the HVAC control module calculates the door travel range. The HVAC control module compares the total number of pulses to calibrated limits. If the total pulse count is less than or equal to the maximum calibrated limited and more that or equal to the minimum calibrated limit, then the calibration is considered successful.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC B0414 Temperature Control 1 Feedback Circuit Range/Performance |
| • | DTC B0424 Temperature Control 2 Feedback Circuit Range/Performance |
| • | DTC B3748 Air Flow Control 3 Feedback Circuit Range/Performance |
| • | DTC B3749 Air Flow Control 7 Feedback Circuit Range/Performance |
Conditions for Running the DTC
The HVAC control module has performed an actuator index.
Conditions for Setting the DTC
DTC P0560 is not set.
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 100 fault free ignition cycles. |
| • | The DTC can be cleared with a scan tool. |
Diagnostic Aids
| • | Inspect the appropriate actuator door and actuator for the following conditions: |
| - | A misaligned actuator. Refer to the following: |
| - | Broken or binding linkages or actuator door |
| - | Obstruction that prevents the actuator door from operating within its full range of motion |
| - | Missing seals to the actuator door |
| - | Misaligned seals to the actuator 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 drives the actuator in one direction. The actuator shaft will not move if the actuator door is already in the position you are attempting to drive it to.
-
This step drives the actuator in the opposite direction.
Step | Action | Values | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | ||||||||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||||
2 | Test the appropriate door control A circuit and the appropriate 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 10 | Go to Step 3 | ||||||||||
Does the actuator shaft rotate? | -- | Go to Step 7 | Go to Step 4 | |||||||||||
Does the actuator shaft rotate? | -- | Go to Step 7 | Go to Step 5 | |||||||||||
5 | Inspect the appropriate door and actuator for the following conditions:
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 6 | ||||||||||
6 | Inspect for poor connections at the harness connector of the appropriate 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 10 | Go to Step 8 | ||||||||||
7 | 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 10 | Go to Step 9 | ||||||||||
8 |
Important: Perform the recalibration procedure for the appropriate actuator. Replace the appropriate actuator. Refer to the following: Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||||||
9 | Replace the HVAC control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||||||
10 |
Does the DTC reset? | -- | Go to Step 2 | System OK | ||||||||||
