Circuit Description
The temperature sense and display system includes a vehicle mounted variable resistance outside air temperature sensor interfaced to the IBCM analog input. The IBCM provides the logic for reading the sensor, filtering the data and transmitting this information via the GM LAN Low Speed Bus to the instrument panel cluster (IPC) for display. 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. The IBCM reads the Outside Air Temperature sensor and converts A-D value to a temperature via a look-up table. 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 IBCM provides sensor out-of-range detection and compensates for engine temperature by utilizing vehicle speed and engine off time duration. The IPC shall display the outside air temperature. The temperature information is provided by the Outside Air Temperature corrected value GM LAN Signal. This information is in Degrees Celsius. The IPC will convert to Degrees Fahrenheit, if necessary. English or metric mode information is available via the Display Measurement System GM-LAN signal. 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 will be believable. 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 will produce false ambient temperature readings attributable to engine heat. A falling outside air temperature sensor reading is always accepted and filtered into the display. Falling temperature readings are always believable but need some light filtering. |
| • | 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 numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: HVAC Schematics in HVAC Systems - Automatic Connector End View Reference: HVAC Connector End Views in HVAC Systems - Automatic DEFINITION: The outside air temperature display on the driver information center (DIC) or radio display cannot be adjusted, or is inaccurate. | ||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||
2 | Did a DTC B0158 code set? | -- | Go to Step 3 | |||||
3 |
Important: The source for checking for the actual ambient temperature should not be taken from a radio station or a sign displaying the temperature. A type of tool to use to measure temperature should be an item such as a thermometer.
Does the temperature displayed on the radio show an accurate temperature reading? | -- | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 4 | ||||
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Important:
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 in Wiring Systems. 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 in Wiring Systems. 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 in Wiring Systems. 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 in Wiring Systems. 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 in Stationary Windows. Did you complete the replacement? | -- | Go to Step 11 | -- | ||||
10 | Replace the radio. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | -- | ||||
11 |
Did you correct the condition? | -- | -- | Go to Step 2 | ||||
