Circuit Description
The outside air temperature sensor is a variable resistor interfaced to the body control module (BCM) analog input. The BCM provides the logic for reading the sensor, filtering the data and transmitting the information via the GM LAN Low Speed Bus to the instrument panel cluster (IPC) for display in the radio. The radio display also serves as the driver information center (DIC) and the outside air temperature is displayed by the IPC in the DIC. The temperature is sent to the IPC in Degrees Celsius. The IPC is responsible for displaying the temperature and converting to Degrees Fahrenheit if necessary. Two GM LAN Low Speed Bus signals are ultimately generated. An un-filtered value, and a filtered value for use by the IPC display. The BCM also provides the sensor out-of-range detection and compensates for engine temperature by utilizing vehicle speed and engine off time duration. The algorithm for all messages is executed at a rate of once every 1 second.
Diagnostic Aids
| • | The following variable represents the latest temperature value to be displayed by the IPC. This variable can be Degrees Celsius or Degrees Fahrenheit. Range: -40 to +87.5°C (-40 to +190°F). The default readout is 87.5°C (190°F). |
| • | After the ignition has been shut OFF and the engine is not running, the outside air temperature sensor must cool down for a period of time before the outside air temperature sensor reading is accurate. This is because the engine produces considerable heat after it has been shutdown. Without air movement across the sensor such as when the vehicle is moving, the outside air temperature sensor produces a false ambient temperature reading attributable to engine heat. A falling outside air temperature sensor reading is always accepted and filtered into the display. |
| • | Upon initial vehicle start-up, the outside air temperature sensor speed counter estimates the amount of time the vehicle will need to be in motion before the outside air temperature sensor will be reading true ambient temperature. As soon as the counter reaches this point it is assumed the driver has been driving the given amount of time for the sensor to cool to ambient. At this point the outside air temperature readings are filtered into the display. |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics , Instrument Cluster Schematics or Body Control System Schematics Connector End View Reference: HVAC Connector End Views DEFINITION: The outside air temperature display on the driver information center (DIC) or radio display cannot be adjusted, or is inaccurate. The DIC is located in the radio display. | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 | Did a DTC B0158 code set? | -- | Go to Step 3 | |
3 |
Important: A thermometer is a proper tool to use when checking the actual ambient temperature. Ambient temperature should not be taken from a radio station or a sign displaying temperature.
Does the temperature displayed on the DIC show an accurate temperature reading? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 4 |
|
Important: Verify the resistance settings with a DMM.
Is the resistance within the table min / max ohm parameters for the stated °C / °F temperature? | -- | Go to Step 5 | Go to Step 7 | |
5 | Test the ambient air temperature sensor signal circuit for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 6 |
6 | Test the ground circuit of the ambient air temperature sensor for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 |
7 | Inspect for poor connections at the harness connector of the ambient 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 11 | Go to Step 9 |
8 | Inspect for poor connections at the harness connector of the radio. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 |
9 | Replace the Ambient Air Temperature Sensor. Refer to Ambient Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
10 | Replace the radio. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- |
11 |
Did you correct the condition? | -- | -- | Go to Step 2 |
