GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B3579

Circuit Description

The auxiliary HVAC control module monitors the air temperature in the upper auxiliary discharge duct via an upper auxiliary air temperature sensor. When the air is cold, the sensor resistance and signal voltage are high. When the air is warm, the sensor resistance and signal voltage are low. The auxiliary HVAC control module converts this voltage to a digital signal that can be transmitted over the keyboard display driver (KDD) data bus to the HVAC control module. The HVAC control module contains the logic that monitors the auxiliary air temperature and is responsible for setting the DTC.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The auxiliary HVAC control module 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 module. The actual value of the sensor will be displayed on the scantool.

Conditions for Clearing the DTC
    • The DTC will become history if the auxiliary HVAC control module 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:

    • Visually inspect the sensor for contamination or damage.
    • Verify that air flow to sensor is not restricted.
    • Verify that the sensor is installed properly.
    • If condition not present refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Test Description

The number(s) below refer to the step number(s) 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.

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

1

Did you perform the HVAC Diagnostic System Check?

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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 Aux. Upper Outlet Temp. parameter in the Auxiliary ECC Data list.

Does the scan tool indicate that the Aux. Upper Outlet Temp. 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 upper auxiliary air temperature sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Aux. Upper Outlet Temp. parameter.

Does the scan tool indicate that the Aux. Upper Outlet Temp. parameter is greater than the specified value?

250 Counts

Go to Step 4

Go to Step 5

4

  1. Turn OFF the ignition.
  2. Connect a 3 amp fused jumper wire between the signal circuit of the upper auxiliary air temperature sensor and the low reference circuit of the upper auxiliary air temperature sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Aux. Upper Outlet Temp. parameter.

Does the scan tool indicate that the Aux. Upper Outlet Temp. parameter is less than the specified value?

5 Counts

Go to Step 8

Go to Step 6

5

Test the signal circuit of the upper auxiliary air temperature sensor 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 12

Go to Step 9

6

Test the signal circuit of the upper auxiliary air temperature sensor 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 12

Go to Step 7

7

Test the low reference circuit of the upper auxiliary air temperature sensor 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 12

Go to Step 9

8

Inspect for poor connections at the harness connector of the upper auxiliary air temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

9

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

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

Replace the upper auxiliary air temperature sensor. Refer to Air Temperature Sensor Replacement - Upper Auxiliary .

Did you complete the replacement?

--

Go to Step 12

--

11

Important: Perform the recalibration procedure for the auxiliary HVAC control module.

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

Did you complete the replacement?

--

Go to Step 12

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12
  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