GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2003 🢒 Aurora 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC B0126, B0131, B0159, B0164, B0174, or B0179

Circuit Description

The following DTC's are for the air temperature sensors:

    • Upper right air temperature sensor
    • Lower right air temperature sensor
    • Ambient air temperature sensor
    • Inside air temperature sensor
    • Upper left air temperature sensor
    • Lower left air temperature sensor

The instrument panel integration module (IPM) monitors the air temperature sensors. The air temperature sensors are variable resistors. The IPM supplies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The IPM provides the ground to the air temperature sensors through the low reference circuit. The IPM monitors the voltage drop across the air temperature sensors and uses the inputs for automatic control calculations. When the air temperatures are cold, the resistance of the sensors are high and the voltage signals are high. When the air temperatures are hot, the resistance of the sensors are low and the voltage signals are low. The IPM converts the voltage values to count values where 1 V is approximately equal to 51 counts.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC

The IPM detects the sensor signal circuit is less than 0.09 volts (5 counts) or greater than 4.90 volts (250 counts)

Action Taken When the DTC Sets
    • HVAC duct temperature sensor
       - When the ambient air temperature is at or below 15°C (59°F), a default value of 4.80 volts (245 counts) will be substituted for the HVAC duct temperature sensor data by the IPM. The Duct Temp displayed on the scan tool, 31°C (88°F) in the HVAC Sensors data list, will be the default value. The Duct Temp displayed on the can tool in the Open/Short Data list will be the actual value.
       - When the ambient air temperature is at or above 16°C (60°F), a default value of 0.19 volts (10 counts) will be substituted for the HVAC duct temperature sensor data by the IPM. The Duct Temp displayed on the scan tool, 119°C (246°F) in the HVAC Sensor data list, will be the default value. The Duct Temp displayed on the scan tool in the Open/Short Data list will be the actual value.
    • Ambient air temperature sensor
       - A default value of 2.50 volts (128 counts) will be substitutes for the ambient air temperature sensor data by the IPM. The Outside Air Temp displayed on the scan tool in Open/Short Data list will be the actual value.
       - The HVAC control module will display -- -- for ambient air temperature when OFF.
       - The HVAC control module will display the set temperature when ON.
    • Inside air temperature sensor
        A default value of 2.5 volts (128 counts) will substituted for the inside air temperature sensor data by the IPM. The Inside Air Temp displayed on the scan tool, 24°C (76°F) in the HVAC Sensor data list, will be the default value. The Inside Air Temp display on the scan tool in the Open/Short Data list will be the actual value.
    • Inside air temperature sensor
        A default value of 2.5 volts (128 counts) will be substituted for the inside air temperature sensor data by the IPM. The Inside Air Temp displayed on the scan tool, 24°C (76°F) in the HVAC Sensor data list, will be the actual value.

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

Test Description

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

  1. The operating range of the sensor is between 0.09 and 4.90 volts. If the scan tool displays a value between 0.08 and 5.0 volts, the sensor is performing outside its designed limits.

    2.

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

    3.

  3. 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.

    4.

  4. Tests the signal circuit for a short to ground.

    5.

  5. Tests the signal circuit for a short to voltage, high resistance or an open.

    6.

  6. Tests the low reference circuit for a high resistance or an open.

Step

Action

Values

Yes

No

Schematic Reference: HVAC Schematics

Connector End View Reference: HVAC Connector End Views

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 appropriate temperature sensor parameter in the Instrument Panel Module Open/Short Data list.

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

0.09-4.90 V

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

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 temperature sensor parameter.

Does the scan tool indicate that the temperature sensor parameter is more than the specified value?

4.90 V

Go to Step 4

Go to Step 5

4

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the air temperature sensor signal circuit 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 temperature sensor parameter.

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

0.09 V

Go to Step 8

Go to Step 6

5

Test the appropriate signal circuit of the 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 appropriate signal circuit of the 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 appropriate low reference circuit 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 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 instrument panel integration module (IPM). Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

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

--

Go to Step 12

--

11

Important: Perform the recalibration procedure for the IPM.

Replace the IPM.

Refer to Instrument Panel Module Replacement .

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