GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Eldorado 🢒 DTC 🢒 DTC B1340

Circuit Description

The HVAC control processor commands the left air temperature actuator to move by controlling the voltage supplied on the control circuit. A low voltage of 0 volts moves the door toward full hot. A voltage of 2.5 volts stops the door. A high voltage of 5 volts moves the door toward full cold. The HVAC control processor determines the current position of the actuator by monitoring the voltage on the signal circuit. The feedback potentiometer is a function of the motor position. A high voltage of 4-5 volts indicates full cold door position. A low voltage of less than 1 volt indicates full hot door position. The HVAC control processor controls the left air temperature actuator door positions in order to maintain the selected air temperature.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The HVAC control processor detects the signal circuit is less than 5 counts (0.09 V) or greater than 250 counts (4.90 V).

Action Taken When the DTC Sets

A default value will be used for the sensor data by the HVAC control processor in an attempt to maintain the air temperature selected by the driver.

Conditions for Clearing the DTC
    • The DTC will become history if the HVAC control processor no longer detects a failure.
    • The history DTC will clear after 50 fault-free ignition cycles.
    • The DTC can be cleared with a scan tool.

Diagnostic Aids

Check the following conditions:

    • A disconnected or broken door may also set this DTC by allowing the left air temperature actuator to travel to its internal stops (overtravel condition).
    • If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

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

  1. Tests for the proper operation of the circuit in the high voltage range.

    2.

  2. Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

    3.

  3. Tests for a short to ground in the 5 volt reference circuit.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

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, observe the Act Dr. Mix Door Position parameter in the Heating and Air Conditioning Data list.

Does the scan tool indicate that the Act Dr. Mix Door Position parameter is within the specified range?

5-250 counts

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the left air temperature actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Act Dr. Mix Door Position parameter.

Does the scan tool indicate that the Act Dr. Mix Door Position parameter is greater than the specified value?

250 counts

Go to Step 4

Go to Step 8

4

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the signal circuit of the left air temperature actuator and the low reference circuit of the left air temperature actuator.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Act Dr. Mix Door Position parameter.

Does the scan tool indicate that the Act Dr. Mix Door Position parameter is less than the specified value?

5 counts

Go to Step 5

Go to Step 9

5

  1. Turn OFF the ignition.
  2. Disconnect the fused jumper wire.
  3. Connect a 3-amp fused jumper wire between the 5 volt reference circuit of the left air temperature actuator and the signal circuit of the left air temperature actuator.
  4. Turn ON the ignition, with the engine OFF.
  5. With a scan tool, observe the Act Dr. Mix Door Position parameter.

Does the scan tool indicate that the Act Dr. Mix Door Position parameter is greater than the specified value?

250 counts

Go to Step 7

Go to Step 6

6

Test the 5 volt reference circuit of the left air temperature actuator for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

7

Test the 5 volt reference circuit of the left air temperature actuator for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

8

Test the signal circuit of the left air temperature actuator for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

9

Test the signal circuit of the left air temperature actuator for a short to voltage, a high resistance, or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 10

10

Test the low reference circuit of the left air temperature actuator for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

11

Inspect for poor connections at the harness connector of the left air temperature actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Special Tools in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

12

Inspect for poor connections at the harness connector of the HVAC control processor. Refer to Testing for Intermittent Conditions and Poor Connections and Special Tools in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

13

Important: Perform the recalibration procedure for the left air temperature actuator.

Replace the left air temperature actuator. Refer to Air Temperature Actuator Replacement - Left Side .

Did you complete the replacement?

--

Go to Step 15

--

14

Important: Perform the recalibration procedure for the HVAC control processor.

Replace the HVAC Control processor. Refer to HVAC Control Processor Replacement .

Did you complete the replacement?

--

Go to Step 15

--

15
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK