Circuit Description
The actuators are a 5-wire bi-directional electric motor. Two control circuits enable the actuators to operate. The control circuits use either a 0 or 12-volt value to coordinate 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 actuators in the opposite direction. The HVAC control module determines the door position by counting motor pulses on one of the control circuits. These pulses are small voltage fluctuations that occur when the brush is shorted across 2 commutator contacts as the motor rotates. As the actuator shaft rotates, the HVAC control module monitors the voltage drop across an internal resistance to detect the pulses. The HVAC control module converts the pulses to counts with a range of 0-255 counts. The HVAC control module uses a range of 0-255 counts to index the actuator position.
When a calibration or recalibration procedure is performed, the HVAC control module calculates the door travel range. The HVAC control module commands the actuator to each extreme position and counts the total number of pulses. 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 limit and greater than or equal to the minimum calibrated limit, then the calibration is considered successful.
| • | Temperature control 1 circuit refers to the air temperature actuator. |
| • | Air flow control 3 circuit refers to the mode actuator. |
| • | Air flow control 7 circuit refers to the recirculation actuator. |
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC B0248 Air Flow Control 3 Circuit |
| • | DTC B0268 Air Flow Control 7 Circuit |
| • | DTC B0408 Temperature Control 1 Circuit |
This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .
DTC Symptom | DTC Symptom Descriptor |
|---|---|
04 | Open Circuit |
51 | Calibration Failure |
61 | Actuator Stuck |
2A | Too Many Pulses |
Conditions for Running the DTC
| • | The ignition is turned ON. |
| • | The ignition voltage is between 9-16 volts. |
Conditions for Setting the DTC
B0248, B0268, or B0408 2A and 61
Sets after 2 occurrences of the test fail code setting conditions listed below in the same ignition cycle.
B0248, B0268, or B0408 51 and 04
Sets after one occurrence of the test fail code setting conditions listed below in the same ignition cycle.
B0248, B0268, or B0408 2A, 04, 51 and 61
The following failures occur and set the DTC:
| • | The HVAC control module does not detect any movement of the actuator. |
| • | The HVAC control module detects a measured actuator range that exceeds the calibratible value. |
| • | The HVAC control module detects a measured actuator range that is less than the calibratible value. |
| • | The HVAC control module detects a calibratible procedure time that exceeds the calibratible value. |
| • | The HVAC control module detects the actuator motor as stalled before the actuator motor reaches the expected stall at the end of the travel. When the drive voltage is reversed, the motor is unable to move more than a calibratible amount in the other direction. |
| • | The HVAC control module detects the actuator motor as stalled before the actuator motor reaches the expected stall at the end of the travel. But, when the drive voltage is reversed, the motor is able to move more than a calibratible amount in the other direction. |
Action Taken When the DTC Sets
B0248, B0268, or B0408 2A
The HVAC control module will use a default range to retry calibration procedure when the ignition is OFF.
B0248, B0268, or B0408 61
The HVAC control module will stop trying to move the air temperature actuator motor during the current ignition cycle.
B0248, B0268, or B0408 04
The HVAC control module will retry the command to move the actuator in a certain direction in 5-minute intervals.
B0248, B0268, or B0408 51
The HVAC control module will retry calibration when the ignition is OFF.
Conditions for Clearing the MIL/DTC
| • | The DTC will become history if the HVAC control module no longer detects a failure. |
| • | The history DTC will clear after 40 fault-free ignition cycles. |
| • | The DTC can be cleared with a scan tool. |
Diagnostic Aids
| • | Inspect the actuator door and actuator for the following conditions: |
| - | A misaligned air temperature actuator--Refer to Temperature Valve Actuator Replacement . |
| - | 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 |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies that the HVAC control module is able to command the appropriate actuator through its full range of motion.
-
This step verifies the position of the actuators.
-
If the actuator does not move at all, the problem is likely to be the drive circuitry within the HVAC control module, 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 actuator door or actuator door linkage.
-
This step drives the actuator in one position. 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 | |||||||||||
Does the scan tool indicate that the value of the Door 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, recheck the Actuator Position parameter in the HVAC control module data list. Does the scan tool display correct values? | -- | Go to Diagnostic Aids | Go to Step 8 | |||||||||||
Does the scan tool indicate that the value of the appropriate Door Position parameter changes by more than the specified value? | 0-3 Counts | Go to Step 8 | Go to Step 5 | |||||||||||
5 | Test the door control A circuit and the door control B circuit for the following:
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 6 | ||||||||||
Does the actuator shaft rotate? | -- | Go to Step 10 | Go to Step 7 | |||||||||||
Does the actuator shaft rotate? | -- | Go to Step 10 | Go to Step 8 | |||||||||||
8 | Inspect the appropriate air temperature, recirc door, or mode door 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 appropriate actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . 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 . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 | ||||||||||
11 |
Important: Perform the recalibration procedure for the appropriate actuator after the replacement. Upon fuse replacement, a recalibration of the actuator will occur. Replace the appropriate actuator.
Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||
12 | Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||
13 |
Does the DTC reset? | -- | Go to Step 3 | System OK | ||||||||||
