GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 Yukon XL - 4WD 🢒 DTC 🢒 DTC B0434 or B3764

Circuit Description

The following DTCs are for the auxiliary HVAC door actuators:

    • DTC B0434 is for the auxiliary air temperature actuator.
    • DTC B3764 is for the auxiliary mode actuator.

The auxiliary HVAC control module controls the auxiliary HVAC door actuators to regulate the airflow through the auxiliary 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 auxiliary 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 auxiliary HVAC control module calibrates the travel range of the auxiliary 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.

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 auxiliary HVAC control module will command the actuator to a default position.
    • If the DTC sets because the actuator failed a calibration, the auxiliary 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 auxiliary 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 Wiring Systems.
    • If the DTC sets following a calibration of the door actuator, inspect the door and the actuator for the following conditions:
       - A misaligned actuator
       - 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

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Ensure to observe the correct parameter for each DTC. Aux. Temp Dr. Position is for the auxiliary air temperature actuator. Mode Door Actual is for the auxiliary mode actuator.

    2.

  2. Tests for the proper operation of the circuit in the low voltage range.

    3.

  3. 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.

    4.

  4. Tests for a short to voltage in the 5-volt reference circuit.

    5.

  5. Tests for a high resistance or for an open in the low reference circuit.

    6.

  6. The voltage will vary between 0-5 volts during normal operation. Ensure to observe the actuator driveshaft and the volt meter when jumping the control circuit with 5-volt reference and the ground circuits. The actuator and the auxiliary HVAC control module connectors must be connected during this step.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

1

Did you perform the HVAC Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, observe the Mode Door Actual or Aux. Temp Dr. Position parameter in the Rear Aux. Climate Module data list.

Does the scan tool indicate that the Mode Door Actual or Aux. Temp Dr. Position parameter is within the specified range?

5-250 counts

Go to Step 3

Go to Step 4

3
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the appropriate auxiliary HVAC door actuator ON and OFF while observing the Mode Door Actual or Aux. Temp Dr. Position parameter.

Does the scan tool indicate that the value of the Mode Door Actual or Aux. Temp Dr. Position parameter changes?

--

Go to Diagnostic Aids

Go to Step 13

4

  1. Turn OFF the ignition.
  2. Disconnect the appropriate auxiliary HVAC door actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Mode Door Actual or Aux. Temp Dr. Position parameter.

Does the scan tool indicate that the Mode Door Actual or Aux. Temp Dr. Position parameter is less than the specified value?

5 counts

Go to Step 5

Go to Step 11

5

  1. Turn OFF the ignition.
  2. Connect a 3-ampere fused jumper between the 5-volt reference circuit and the appropriate door position signal circuit of the auxiliary HVAC door actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Mode Door Actual or Aux. Temp Dr. Position parameter.

Does the scan tool indicate that the Mode Door Actual or Aux. Temp Dr. Position parameter is greater than the specified value?

230 counts

Go to Step 6

Go to Step 9

6

  1. Disconnect the fused jumper.
  2. Measure the voltage between the 5-volt reference circuit and the low reference circuit of the auxiliary HVAC door actuator.

Does the voltage measure less than the specified value?

5.5 V

Go to Step 7

Go to Step 8

7

  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable.
  3. Measure the resistance from the low reference circuit of the auxiliary HVAC door actuator to a good ground.

Does the resistance measure less than the specified value?

5 ohms

Go to Step 17

Go to Step 12

8

Test the 5-volt reference circuit of the appropriate auxiliary HVAC door actuator for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

9

Test the 5-volt reference circuit of the appropriate auxiliary HVAC door actuator for a short to ground, for a high resistance, or for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 10

10

Test the appropriate door position signal circuit of the auxiliary HVAC door actuator for a short to ground, for a high resistance, or for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

11

Test the appropriate door position signal circuit of the auxiliary HVAC door actuator for a short to voltage. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

12
  1. Disconnect the auxiliary HVAC control module.
  2. Test the low reference circuit of the appropriate auxiliary HVAC door actuator for a high resistance or for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

13

  1. Observe the appropriate auxiliary HVAC door actuator drive shaft.
  2. Backprobe and monitor the voltage from the signal circuit of the air temperature door actuator to a good ground.
  3. Connect a 3-amp fused jumper wire between appropriate door control circuit at the auxiliary HVAC control module and a good ground.
  4. Disconnect the fused jumper wire.
  5. Connect a 3-amp fused jumper wire between the appropriate door control circuit and the 5-volt reference circuit at the auxiliary HVAC control module.

Does the drive shaft of the appropriate auxiliary HVAC door actuator rotate?

--

Go to Step 18

Go to Step 14

14

Test the door control circuit of the appropriate auxiliary HVAC door actuator for a short to voltage, for a short to ground, or for an open. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 15

15

Test the ignition 3-voltage circuit of the appropriate auxiliary HVAC door actuator for an open or a high resistance. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 16

16

Test the ground circuit of the appropriate auxiliary HVAC door actuator for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

17

Inspect for poor connections at the harness connector of the appropriate auxiliary HVAC door actuator. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 19

18

Inspect for poor connections at the harness connector of the auxiliary HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

19

Important: Perform the calibration procedure for auxiliary HVAC door actuators.

Replace the auxiliary HVAC door actuator. Refer to the appropriate replacement procedure:

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the auxiliary HVAC control module. Refer to Auxiliary Heater and Air Conditioning Control Module Replacement .

Did you complete the replacement?

--

Go to Step 21

--

21
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle according to the Conditions for Running in the DTC, as specified in the supporting text.

Does the DTC set again?

--

Go to Step 2

System OK