B3770 - HVAC Systems - Automatic

DTC B3770

CIRCUIT DESCRIPTION
The following DTCs are for the HVAC door actuators:
- B0229 is for the recirculation actuator.
- B0414 is for the left air temperature actuator.
- B0424 is for the right air temperature actuator.
- B3770 is for the mode actuator.

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The module supplies a 5-volt source voltage to the potentiometer on the 5-volt reference circuit. The module supplies ground to the potentiometer through the low reference circuit. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The module converts the voltage value to a count value where 1 volt is approximately equal to 51 counts.

The HVAC control module calibrates the travel range of the HVAC door actuators when it is initially powered by the battery positive voltage circuit. During calibration, the module commands the actuators in each direction until door travel is stopped. The module stores the minimum door positions and the maximum door positions of each actuator into memory. The total travel range is calculated by subtracting the minimum door position from the maximum door position. The door actuators can be calibrated again with a scan tool.

DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC B0229 Recirculate Position Feedback Circuit Range/Performance
- DTC B0414 Temperature Control 1 Feedback Circuit Range/Performance
- DTC B0424 Temperature Control 2 Feedback Circuit Range/Performance
- DTC B3770 Air Flow Control 6 Feedback Circuit

CONDITIONS FOR RUNNING THE DTC
- Battery voltage is 8.7-16.5 volts.
- The ignition is ON.

CONDITIONS FOR SETTING THE DTC
The DTC sets when one of the following conditions are present:
- The actual door position value for the actuator is less than 5 counts.
- The actual door position value for the actuator is greater than 250 counts.
- The actuator fails calibration because the calculated travel range value is too great or too small.

ACTION TAKEN WHEN THE DTC SETS
- If the DTC sets because the actual door position value is out of range, the HVAC control module will command the actuator to a default position.
- If the DTC sets because the actuator failed a calibration, the HVAC control module will attempt to calibrate the motor in the next transition from OFF to RUN mode.

CONDITIONS FOR CLEARING THE DTC
- The DTC will become history if the HVAC control module no longer detects the condition that set the DTC.
- The history DTC will clear after 100 fault-free ignition cycles.
- The DTC can be cleared with a scan tool.

DIAGNOSTIC AIDS
- If the condition is not present refer to Testing for Intermittent Conditions and Poor Connections in Diagnostic Aids.
- If the DTC sets following a calibration of the door actuator, inspect the door and the actuator for the following conditions:
- A misaligned actuator
- Broken linkages or binding linkages
- A broken door or a binding door
- An obstruction that prevents the door from operating within the full range of motion
- Missing seals to the door
- Poor connections at the harness connector of the door actuator
- If a signal circuit of an actuator is short to ground and the resistance across the internal potentiometer is low, then this condition could cause a multiple DTC concern.

TEST DESCRIPTION

Steps 1-9:

Steps 10-20:

Steps 21-22:

The numbers below refer to the step numbers on the diagnostic table.
3. At least 2 of the DTCs must be set as current DTC to ensure correct diagnosis. If only one DTC is present then the answer is No.
5. This step tests for the proper operation of the circuit in the low voltage range.
6. This step tests for the proper operation of the circuit in the high voltage range. If the jumper fuse opens when you perform this test, the circuit is shorted to ground.
7. This step tests for a short to voltage in the 5-volt reference circuit.
8. This step tests for a high resistance or for an open in the low reference circuit.
9. This step tests for an open on the low reference circuit that is common to all of the actuators. Choose the easiest HVAC door actuator that set a DTC to start the diagnosis.
10. Disconnecting each actuator, one at a time, isolates the disconnected actuators signal circuit from the 5-volt reference circuit that is common to all the actuators.