For 1990-2009 cars

### Circuit Description

The ambient air outside temperature sensor is located behind the lower grille of the front fascia on the left side of the vehicle. In this position, it is exposed at airflow through the grill before the air enters the radiator. This provides a sample of the ambient air temperature.

The sensor is a thermistor used to control the signal voltage to the heater and A/C control. The heater and A/C control supplies a reference voltage (about 5 volts) on circuit PM 4 to the sensor and measures the voltage drop in the circuit to obtain a temperature signal. This signal is an input that tells the heater and A/C control how much cooling or heating will be required to deliver to the passenger compartment. It also affects the mode and blower motor speed.

Resistance of the sensor varies from 169,400 ohms at -40°C (-40°F) to 1,245 ohms at 60°C (140°F). When the ambient air temperature is cold, the thermistor resistance is high; therefore, the heater and A/C control will receive a high signal voltage input. If the air temperature is hot, the thermistor resistance is low, the heater and A/C control will receive a low signal voltage input.

The ambient temperature is displayed on the display panel of the heater and A/C control. The displayed temperature value is derived from a series of calculations performed by a processor in the heater and A/C control. When the measured ambient temperature is less than the displayed value, the processor filters less of the input signal, stores it in EEPROM, and rapidly updates the display. If the measured ambient temperature is greater than the displayed value and the vehicle is moving, the processor filters more of the input signal, stores it in EEPROM, and updates the display at a much slower rate.

### Conditions for Setting the DTC

• | With the ignition in the ON position, circuit PM4 is checked continuously every 200 ms.

• | Circuit PM4 stays at 4.5 V or higher.

### Action Taken When the DTC Sets

• | The heater and A/C control displays the ambient temperature as F.

• | The system uses a default value.

### Conditions for Clearing the DTC

• | The conditions for the fault are no longer present

• | Using a scan tool.

• | A history DTC will clear after 20 consecutive ignition cycles if the condition for the fault is no longer present.

### Diagnostic Aids

If condition not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

°C | °F | Ohmsohms
--- | --- | ---
Temperature vs. Resistance Values (Approximate)
-40 | -40 | 169,400
-30 | -22 | 88,740
-20 | -4 | 48,580
-10 | 14 | 27,670
0 | 32 | 16,330
10 | 50 | 9,951
20 | 68 | 6,246
30 | 86 | 4,028
40 | 104 | 2,663
50 | 122 | 1,801
60 | 140 | 1,245

### Test Description

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

1. Scan tool uses a default value, this will not give accurate reading of sensor value if open or short to ground.

2. Tests for the possibility of a short to voltage.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: HVAC Schematics
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - HVAC Systems - Automatic
2 |

1. Turn OFF the ignition.
2. Disconnect the ambient air outside temperature sensor.
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage from circuit PM4 of the ambient air outside temperature sensor to a good ground.

Does the voltage measure near the specified value?

5 V

Go to Step 3

Go to Step 4

3 | Measure the voltage from circuit PM4 to circuit P11 of the ambient air outside temperature sensor. Does the voltage measure near the specified value? | 5 V | Go to Step 6 | Go to Step 5
4 | Test circuit PM4 of the ambient air outside 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 12 | Go to Step 9
5 | Test circuit P11 of the ambient air outside 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
6 | Inspect for poor connections at the harness connector of the ambient air outside temperature sensor. 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 ambient air outside temperature sensor resistance. Does the resistance measure near the Sensor Resistance Table value? | -- | Go to Step 8 | Go to Step 10
8 |

1. Disconnect the heater and A/C controls.
2. Turn ON the ignition, with the engine OFF.
3. Test circuit PM4 of the ambient air outside temperature sensor for a short to voltage. 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

9 | Inspect for poor connections at the harness connector of the heater and A/C controls. 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 ambient air outside temperature sensor. Refer to Ambient Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
11 | Important:: Perform the recalibration procedure for the heater and A/C controls. Replace the heater and A/C controls. Refer to HVAC Control 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