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. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|
Outside Air Temperature (OAT) Signal Circuit | B0158 06 | B0158 04 | B0158 05 |
Outside Air Temperature (OAT) Ground Reference Circuit | -- | B0158 04 | -- |
Circuit/System Description
The HVAC module monitors the signal circuit of the ambient air temperature sensor. The ambient air temperature sensor is a thermistor which varies in resistance as the temperature changes. When the resistance of ambient air temperature sensor increases, the ambient air temperature is cold. When the resistance of the ambient air temperature sensor decreases, the ambient air temperature is high. The HVAC module interfaces with the ambient air temperature via the ambient air temperature sensor signal circuit. The HVAC module applies 5 volts to an internal input resistor that is connected to the ambient air temperature sensor signal circuit. The HVAC module uses the ambient air temperature resistance and voltage for automatic control calculations and conversion to temperature values. The HVAC module sends the temperature value to the instrument panel cluster (IPC) via the serial data circuit for display in the driver information center (DIC). If the ambient air temperature sensor is opened or shorted, the temperature display is either a cold or hot extreme. An open sensor will display -40°F (-40°C) in the DIC and a sensor shorted to ground displays +189.5°F (+87.5°C).
Diagnostic Aids
| • | The following variable represents the latest temperature value to be displayed by the DIC. This variable can be Degrees Fahrenheit or Celsius. |
| Range: -40°F to +189.5°F (-40°C to +87.5°C). The default readout is 190°F (87.5°C). |
| • | After the ignition has been shutoff and the engine is not running, the ambient air temperature sensor must cool down for a period of time before the sensor reading is accurate. This is because the engine produces considerable heat after it has been shutdown. Without air movement across the ambient air temperature sensor such as when the vehicle is moving, the sensor provides a false ambient air temperature reading that can be attributed to engine heat. A falling ambient air temperature sensor reading is always accepted and filtered into the display. |
| • | Upon initial vehicle startup, the ambient air temperature sensor speed counter estimates the amount of time the vehicle will need to be in motion before the sensor reads the true ambient air temperature. As soon as the counter reaches the point, it is assumed the driver has been driving the given amount of time for the sensor to cool to ambient temperature. At this point the ambient air temperature readings are filtered into the display. |
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
The DIC should display +189.5°F (+87.5°C) or -40°F (-40°C) .
Circuit/System Testing
- Ignition OFF, disconnect the ambient air temperature sensor connector.
- Ignition OFF, test for less than 1 ohm of resistance between the ground circuit terminal B and ground.
- Ignition ON, verify the driver information center (DIC) displays approximately -40°F (-40°C).
- Ignition ON, perform an ambient air temperature Instant Update to by pass filtering by simultaneously pressing the following switches on the HVAC control module:
- Ignition ON, install a 3-amp fused jumper wire between the signal circuit terminal A and the ground circuit terminal B. Verify the DIC displays approximately 189.5°F (87.5°C).
- If all circuits test normal, test or replace the ambient air temperature sensor.
| ⇒ | If greater than the specified value, test the ground circuit for an open/high resistance. |
| ⇒ | If the DIC does not display approximately -40°F (-40°C), test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC module. |
| • | LEFT TEMPERATURE UP |
| • | PASS ENABLE |
| • | REAR DEFOG ENABLE |
| ⇒ | If the DIC does not display approximately 189.5°F (87.5°C), test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for the HVAC module replacement, setup and programming |
