GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The following DTCs are for the auxiliary air temperature sensors located in the auxiliary HVAC ducts:

    • B3579 is for the upper auxiliary air temperature sensor.
    • B3584 is for the lower auxiliary air temperature sensor.

The auxiliary air temperature sensors allow the auxiliary HVAC control module to monitor the temperature of the discharge air in the auxiliary HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The auxiliary HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The auxiliary HVAC control module converts the voltage values to count values where 1 volt is approximately equal to 51 counts.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC B3579 Output Air Temperature Sensor 6 Circuit Range/Performance
    • DTC B3584 Output Air Temperature Sensor 7 Circuit Range/Performance

Conditions for Running the DTC

    • Battery voltage is within 8.7-16.5 volts.
    • The ignition is ON.

Conditions for Setting the DTC

The auxiliary HVAC control module determines that the value of the air temperature parameter is less than 5 counts or greater than 250 counts.

Action Taken When the DTC Sets

The auxiliary HVAC control module uses a default air temperature value for further automatic control calculations. The default values are displayed on the scan tool. The default value is 50 counts.

Conditions for Clearing the DTC

    • The DTC will become history if the auxiliary HVAC control module no longer detects a fault.
    • The history DTC will clear after 100 fault-free ignition cycles.
    • The DTC can be cleared with a scan tool.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step verifies that the condition that set the DTC is present.

Step

Action

Value(s)

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Select the Rear Aux. Climate Module display DTC function on the scan tool.

Does the scan tool indicate that B3579 or B3584 is a current DTC?

--

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3

  1. Turn OFF the ignition.
  2. Disconnect the appropriate auxiliary air temperature sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the signal circuit of the auxiliary air temperature sensor to a good ground.

Does the voltage measure near the specified value?

5 V

Go to Step 4

Go to Step 5

4

Measure the voltage from the signal circuit to the low reference circuit of the auxiliary air temperature sensor.

Does the voltage measure near the specified value?

5 V

Go to Step 7

Go to Step 6

5

Test the signal circuit of the appropriate auxiliary air temperature sensor for an open, high resistance, short to ground, or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

6

Test the low reference circuit of the appropriate 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 11

Go to Step 8

7

Inspect for poor connections at the harness connector of the appropriate 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 11

Go to Step 9

8

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 11

Go to Step 10

9

Replace the appropriate auxiliary air temperature sensor. Refer to one of the following procedures:

Did you complete the replacement?

--

Go to Step 11

--

10

Replace the auxiliary HVAC control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 11

--

11

  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