Outside Air Temperature Display Inaccurate or Inoperative
Outside Air Temperature Display Inaccurate or Inoperative
Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
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 serial data 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.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the ambient air temperature sensor.
2. Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit and ground.
• If greater than 1 ohm, test the ground circuit for an open/high resistance. If the circuit tests normal, replace the BCM.
3. Ignition ON, verify the scan tool Ambient Air Temp. Sensor parameter is greater than 4.7 volts.
• If less than 4.7 volts, test the signal circuit 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 and ground. Verify the scan tool Ambient Air Temp. Sensor parameter is less than 0.4 volt.
• If greater than 0.4 volt, test the signal circuit for an open/high resistance. If the circuit tests normal replace the BCM.
5. If all circuits test normal, test or replace the ambient temperature sensor.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Ambient Air Temperature Sensor Replacement
* Control Module References for BCM replacement, setup, and programming