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For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2007 🢒 H2 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC B0174, B0179, B0510, or B0515

Circuit Description

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

    • B0174 is for the upper left air temperature sensor.
    • B0179 is for the lower left air temperature sensor.
    • B0510 is for the upper right air temperature sensor.
    • B0515 is for the lower right air temperature sensor.

Air temperature sensors allow the HVAC control module to monitor the temperature of the discharge air in the 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 HVAC control module monitors the voltage drop 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 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 B0174 Output Air Temperature Sensor 1 Circuit Range/Performance
    • DTC B0179 Output Air Temperature Sensor 2 Circuit Range/Performance
    • DTC B0510 Output Air Temperature Sensor 3 Circuit Range/Performance
    • DTC B0515 Output Air Temperature Sensor 4 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 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 HVAC control module uses a default air temperature value for further automatic control calculations. The default values are not displayed on the scan tool.

Conditions for Clearing the DTC
    • The DTC will become history if the 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.

Diagnostic Aids

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections .

Test Description

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

  1. This step verifies that the temperature displayed is not within the calibrated range.

    2.

  2. This step tests for the proper operation of the circuit in the high voltage range.

    3.

  3. The step 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

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

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the appropriate Duct Actual parameter in the Heating and Air Conditioning data list. Refer to one of the following parameters:
    4. • LH AC Duct Actual
    • LH Heater Duct Actual
    • RH AC Duct Actual
    • RH Heater Duct Actual

Does the scan tool indicate that the Duct Actual 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 air temperature sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the appropriate Duct Actual data parameter.

Does the scan tool indicate that the Duct Actual data 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 air temperature sensor and the low reference circuit of the air temperature sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the appropriate Duct Actual data parameter.

Does the scan tool indicate that the Duct Actual data parameter is less than the specified value?

5 Counts

Go to Step 8

Go to Step 6

5

Test the signal circuit of the air temperature sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

6

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

Did you find and correct the condition?

--

Go to Step 12

Go to Step 7

7

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

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 air temperature sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

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 HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

Replace the air temperature sensor. Refer to the appropriate replacement procedure:

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the HVAC control module. Refer to Control Module References for replacement, setup, and programming.

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 within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK