GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Avalanche - 4WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B0263, B0268, B0408, or B0418

Circuit Description

The following DTCs are for the HVAC door actuators:

    • B0263 is for the mode actuator.
    • B0268 is for the recirculation actuator.
    • B0408 is for the left air temperature actuator.
    • B0418 is for the right air temperature 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 logic circuit inside the actuators receives control signals from the HVAC control module and controls the internal stepper motor. When a door positional change is required, the HVAC control module calculates a commanded door position. The module compares the commanded door position to the actual door position and determines the needed direction of motor rotation. The module applies a signal voltage to the door control circuit that is an input to the internal logic circuit of the door actuator. A 5-volt signal increases the door position. A 0-volt signal decreases the door position. When the commanded door position is equal to the actual door position, the HVAC control module sends a 2.5-volt signal to the door actuator and motor rotation stops. The ignition 3-voltage circuit provides source voltage to the logic circuit. The module provides ground to the actuator logic circuit through the low reference circuit.

Conditions for Running the DTC
    • Source voltage is 8.7-16.5 volts.
    • The ignition is ON.
    • The HVAC control module commands the actuator to move.

Conditions for Setting the DTC

The actual door position is not near the commanded door position.

Action Taken When the DTC Sets

The HVAC control module does not command the actuator to move for the remainder of the ignition cycle.

Conditions for Clearing the DTC
    • The DTC becomes history during the next ignition cycle in which the HVAC control module no longer detects a stall condition.
    • 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.
    • Inspect the appropriate door and door actuator for the following conditions:
       - A misaligned door actuator
       - Binding linkages
       - A binding door
       - An obstruction that prevents the door actuator from operating within the full range of motion

Test Description

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

  1. Determines if the HVAC door actuator is stalled.

    2.

  2. Applies control circuit voltage to the input of the HVAC door actuator.

Step

Action

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 a scan tool, command the appropriate HVAC door actuator ON and OFF while observing the corresponding Door Actual parameter.

Does the scan tool indicate that the value of the appropriate Door Actual parameter changes?

Go to Diagnostic Aids

Go to Step 3

3

  1. Observe the appropriate HVAC door actuator drive shaft.
  2. Connect a 3-amp fused jumper wire between appropriate door control circuit at the HVAC control module and a good ground.
  3. Disconnect the fused jumper wire.
  4. Connect a 3-amp fused jumper wire between the appropriate door control circuit and the 5-volt reference circuit at the HVAC control module.

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

Go to Step 8

Go to Step 4

4

Test the door control circuit of the appropriate 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 12

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the fused jumper wire.
  3. Disconnect the appropriate HVAC door actuator.
  4. Turn ON the ignition, with the engine OFF.
  5. Probe the ignition 3-voltage circuit of the appropriate HVAC door actuator with a test lamp that is connected to ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 9

6

Inspect the appropriate door and the door actuator for the following conditions:

    • A misaligned door actuator.
    • Binding linkages
    • A binding door
    • An obstruction that prevents the HVAC door actuator from operating within the full range of motion

Did you find and correct the condition?

Go to Step 12

Go to Step 7

7

Inspect for poor connections at the harness connector of the appropriate 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 12

Go to Step 10

8

Inspect for poor connections at the harness connector of the 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 12

Go to Step 11

9

Repair the ignition 3-voltage circuit of the appropriate HVAC door actuator. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 12

--

10

Important: Perform the calibration procedure for HVAC door actuators.

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

Did you complete the replacement?

Go to Step 12

--

11

Replace the HVAC control module. Refer to HVAC Control Module Replacement .

Did you complete the replacement?

Go to Step 12

--

12
  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