Diagnostic Instructions

DTC Descriptors

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

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Recirculation Door Control A	B0268, B0269, B3749	B0268, B0269, B3749	B0268, B0269, B3749	--
Recirculation Door Control B	B0268, B0269, B3749	B0268, B0269, B3749	B0268, B0269, B3749	--
Left Air Temperature Door Control A	B0408, B0409, B0414	B0408, B0409, B0414	B0408, B0409, B0414	--
Left Air Temperature Door Control B	B0408, B0409, B0414	B0408, B0409, B0414	B0408, B0409, B0414	--
Right Air Temperature Door Control A	B0423, B0419, B0424	B0423, B0419, B0424	B0423, B0419, B0424	--
Right Air Temperature Door Control B	B0423, B0419, B0424	B0423, B0419, B0424	B0423, B0419, B0424	--
Mode Door Control A	B0248, B0249, B3748	B0248, B0249, B3748	B0248, B0249, B3748	--
Mode Door Control B	B0248, B0249, B3748	B0248, B0249, B3748	B0248, B0249, B3748	--

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.

Conditions for Running the DTC

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

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

HVAC Connector End Views

Description and Operation

Electrical Information Reference

Scan Tool Reference

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 or C (mode actuator). 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, test or 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 or C (mode actuator) 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 after completing the diagnostic procedure.