For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC B0158 01: Outside Air Temperature (OAT) Sensor Short to Battery or Open
DTC B0158 02: Outside Air Temperature (OAT) Sensor Short to Ground

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage
--- | --- | --- | --- | ---
Ambient Air Temperature Signal | B0158 | 1 | B0158 | B0158
Ambient Air Temperature Low Reference | -- | 1 | B0158 | --
1. Outside Air Temperature Display Inaccurate or Inoperative

### Circuit/System Description

The ambient air temperature sensor is a variable resistor interfaced to the underhood electrical center (UEC). The ambient air temperature sensor is a 2-wire negative temperature coefficient thermistor. The UEC applies voltage to an internal input resistor connected to the signal circuit of the ambient air temperature sensor. When the ambient air temperature is cold, the sensor resistance is high and the signal voltage is high. When the ambient air temperature is hot, the sensor resistance is low and the signal voltage is low. The UEC provides the logic for reading the sensor, filtering the data and transmitting the information via the serial data circuit to the driver information center (DIC) for display.

### Conditions for Running the DTC

• | The ignition is in ACC or RUN.

• | The system voltage is between 9-16 volts

### Conditions for Setting the DTC

• | The UEC detects that the ambient air temperature sensor is -40°C (-40°F) or less.

• | The UEC detects that the ambient air temperature sensor is 87°C (188°F) or greater.

### Action Taken When the DTC Sets

• | The last valid value is frozen and retained by the ambient air temperature sensor.

• | The driver information center (DIC) will display SET TEMPERATURE when ON.

### Conditions for Clearing the DTC

• | The DTC becomes history when the UEC no longer detects a fault.

• | The history DTC clears after 40 malfunction-free ignition cycles.

### Reference Information

#### Schematic Reference

Instrument Cluster Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Driver Information Center (DIC) Description and Operation

• | Instrument Cluster Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the harness X1 harness connector at the ambient air temperature sensor.
2. Ignition OFF, test for less than 1 ohm between the low reference circuit terminal 2 and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, verify the scan tool Ambient Air Temp. Sensor parameter is approximately -40°C (-40°F).

⇒ | If greater than the specified value, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3-amp fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the scan tool Ambient Air Temp. Sensor parameter is approximately 87°C (188°F).

⇒ | If less than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the UEC.

5. If all circuits test normal, test or replace the ambient air temperature sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Ambient Air Temperature Sensor Replacement

• | Control Module References for the UEC replacement, setup, and programming