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For 1990-2009 cars only

Circuit Description

The HVAC control module monitors air temperature through air temperature sensors. 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 HVAC control module requests A/C compressor clutch engagement and controls the appropriate mode and air temperature actuator door positions in order to maintain the selected air temperature on the HVAC control module.

The inside air temperature sensor is contained within the HVAC control module. The replacement of the inside air temperature sensor involves the replacement of the HVAC control module. The inside air temperature sensor provides the HVAC control module with the temperature of the air drawn through an aspirator from the passenger compartment across a sensor. A reference voltage is supplied to the sensor thermistor and the HVAC control module determines the voltage drop across that device which is proportional to temperature. As the air temperature increases, the resistance decreases and the voltage signal decreases. As the air temperature decreases, the resistance increases and the voltage signal increases.

Output air temperature sensor 1 circuit refers to the a/c upper duct air temperature sensor.

Output air temperature sensor 2 circuit refers to the heater lower duct air temperature sensor.

Passenger compartment temperature sensor 1 circuit refers to the inside air temperature sensor.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC B0164 Passenger Compartment Temperature Sensor Circuit Range/Performance
    • DTC B0174 Output Air Temperature Sensor 1 Circuit
    • DTC B0179 Output Air Temperature Sensor 2 Circuit

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to DTC Symptom Description .

The HVAC control module monitors the signal circuit of the appropriate duct or inside air temperature sensor for the following conditions:

DTC Symptom

DTC Symptom Descriptor

05

Short to Battery or Open

06

Short to Ground or Open

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

B0164 05 and 06

The HVAC control module detects the inside air temperature sensor signal circuit is less than 2 counts or greater than 253 counts for 30 seconds.

B0174 or B0179 05 and 06

The 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

B0164 05 and 06

If the DTC sets due to the low condition, the HVAC control module will default to maximum cooling, except when the maximum heating setting is selected. If the DTC sets due to the high condition, the HVAC control module will default to maximum heating, except when the maximum cooling setting is selected.

B0174 05 and 06

A default value will be used for the sensor data by the HVAC control module.

Conditions for Clearing the DTC

    • The DTC will become history if the HVAC control module no longer detects a failure.
    • The history DTC will clear after 40 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. Tests for the proper operation of the circuit in the high voltage range.

  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

Values

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. Turn ON the ignition, with the engine OFF.
  2. With a scan tool, observe the HVAC DTC List.

Does the scan tool indicate the DTC is current?

--

Go to Step 6

Go to Step 3

3

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Upper and Lower Duct Air Temperature Sensor parameter in the HVAC Control Module Sensor Data list.

Does the scan tool indicate that the Sensor parameter is within the specified range?

5-250 counts (0.09-4.90 V)

Go to Diagnostic Aids

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the upper and lower duct air temperature sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Upper and Lower Duct Temp Sensor parameter in the HVAC control module sensor Data list.

Does the scan tool indicate that the Sensor parameter is greater than the specified value?

250 counts (4.90 V)

Go to Step 5

Go to Step 8

5

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the signal circuit of the upper and lower duct air temperature sensor and the low reference circuit of the sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the Upper and Lower Duct Air Temperature Sensor parameter in the HVAC control module sensor Data list.

Does the scan tool indicate that the Sensor parameter is less than the specified value?

5 counts (0.09 V)

Go to Step 11

Go to Step 9

6

Test the ignition 3 voltage circuit of the HVAC control module for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 7

7

Test the ground circuit of the HVAC control module for an open. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

8

Test the signal circuit of the appropriate duct 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 15

Go to Step 12

9

Test the signal circuit of the appropriate duct 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 15

Go to Step 10

10

Test the low reference circuit of the appropriate duct 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 15

Go to Step 11

11

Inspect for poor connections at the harness connector of the appropriate duct 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 15

Go to Step 13

12

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 15

Go to Step 14

13

Replace the upper or lower duct air temperature sensor. Refer to Duct Air Temperature Sensor Replacement - Upper or Duct Air Temperature Sensor Replacement - Lower .

Did you complete the replacement?

--

Go to Step 15

--

14

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

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