B3749

DTC B0248, B0249, B0268, B0269, B0408, B0409, B0414, B0419, B0423, B0424, B3748, or B3749

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.



DTC Descriptor
DTC B0248
- Airflow Control 3 Circuit

DTC B0249
- Air Flow Control 3 Circuit Range

DTC B0268
- Airflow Control 7 Circuit

DTC B0269
- Air Flow Control 7 Circuit Range

DTC B0408
- Temperature Control 1 Circuit Malfunction

DTC B0409
- Temperature Control 1 Circuit Range/Performance

DTC B0414
- Temperature Control 1 Feedback Circuit Range/Performance

DTC B0419
- Temperature Control 2 Circuit Range/Performance

DTC B0423
- Temperature Control 2 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




Diagnostic Fault Information






Circuit/System Description

The actuator is an electronic stepper motor. The HVAC control module supplies power and ground to the actuator. The HVAC control module controls the direction of the actuator by changing the polarity of the control circuits. When the actuator reaches its desired position, both circuits are fixed to the same value 0 volts. The HVAC control module determines the door or mode film position by counting pulses, voltage fluctuations, caused by the brush to commutator action generated during normal motor operation. The HVAC control module monitors a 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.


When a calibration or recalibration procedure is performed, the HVAC control module calculates the door or mode film travel range. The HVAC control module commands the actuator in one extreme position then counts pulses starting from 0 counts. 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.

* Air flow control 3 circuit refers to the mode actuator.
* Air flow control 7 circuit refers to the recirculation actuator.
* Temperature control 1 circuit refers to the left air temperature.
* Temperature control 2 circuit refers to the right air temperature.



Conditions for Running the DTC

* The ignition is ON.
* Ignition voltage is between 9-16 volts.
* The HVAC module is ON.



Conditions for Setting the DTC

The actual door position differs from the commanded door position by more than 4 counts or the HVAC control module detects the door position signal circuit is less than 7 counts or greater than 250 counts.


Action Taken When the DTC Sets

Driver A and driver B circuits are deactivated for the appropriate actuator.


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.



Reference Information
Schematic Reference

HVAC Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

* Air Temperature Description and Operation (Air Temperature Description and Operation)
* Air Delivery Description and Operation (Air Delivery Description and Operation)

Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information


Circuit/System Verification

1. Engine running, select HVAC manual operation, command the air to flow through the vent outlets, floor outlets, defrost outlets by using the appropriate mode switch on the HVAC control module. The air flow should follow the commanded states and blow through the vent, floor and defrost outlets.
2. Command the air temperature from the full COLD to the full HOT by using the temperature control switch on the HVAC control module. The air temperature should follow the commanded states of full HOT to full COLD through the vent or panel positions.
3. Ignition ON, observe the operation of the drive shaft of the recirculation actuator while using the recirculation control switch on the HVAC control module. The drive shaft of the recirculation actuator should rotate.



Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate actuator.
2. Ignition ON, connect a test lamp between the control circuit terminal A and control circuit terminal B. Command the actuator in each direction. The test lamp should briefly illuminate when commanding the actuator in one direction to the other direction.

• If the test lamp is always OFF, test the appropriate control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
• If the test lamp continuously illuminates, test the appropriate control circuit for a short to B+. If the circuit tests normal, replace the HVAC control module.

3. If all circuits test normal, replace the appropriate actuator.



Component Testing

1. Install a 10-amp fused jumper wire between the control terminal A and 12 volts. Momentarily install a jumper wire between the control terminal B and ground. The appropriate actuator shaft should rotate.

• If the function does not perform as specified, replace the appropriate actuator.

2. Reverse the jumper wires; the appropriate actuator shaft should rotate.

• If the function does not perform as specified, replace the appropriate actuator.




Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Recirculation Actuator Replacement (Recirculation Actuator Replacement)
* Mode Actuator Replacement (Mode Actuator Replacement)
* Control Module References (Programming and Relearning)for HVAC replacement, setup, and programming