GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2007 🢒 DTS 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Outside Air Temperature Display Inaccurate or Inoperative

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

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B0158 04

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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 the 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 sensor via 2 discreet circuits. The HVAC module applies 5 volts to an internal input resistor that is connected to the signal circuit of the ambient air temperature sensor . The HVAC module provides ground through the low reference circuit. The HVAC module uses the ambient air temperature sensor resistance and voltage for automatic control calculations and conversion to temperature values. The HVAC module displays the ambient air temperature and if the ambient air temperature sensor is opened or shorted, the temperature display is either a cold or hot extreme. An open ambient air temperature sensor displays -40°F (-40°C) and an ambient air temperature 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 HVAC module. This variable can be Degrees Fahrenheit or Celsius.
        Range: -40 to +189.5°F ( -40 to +87.5°C). The default readout is 87.5°C (190°F).
    • 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 temperature 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 ambient air temperature sensor provides a false 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 needs to be in motion before reading the true outside temperatures. As soon as the sensor counter reaches the point, it is assumed the driver has driven the given amount of time for the sensor to cool down to the outside temperatures. At this point the ambient air temperature sensor readings are filtered into the display.

Reference Information

Schematic Reference

    •  HVAC Schematics
    •  Instrument Cluster Schematics

Connector End View Reference

    •  HVAC Connector End Views
    •  Displays and Gages Connector End Views
    •  Inline Harness Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

    •  Scan Tool Data List for the automatic system
    •  Scan Tool Data List for displays and gages

Circuit/System Verification

The DIC should display 87.5°C (189.5°F) or -40°C (-40°F) .

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 ambient air temperature sensor low reference circuit terminal B and ground.
    3. ⇒If greater than 1 ohm, test the ambient air temperature sensor low reference circuit for an open/high resistance.
  3. Ignition ON, verify the HVAC module displays approximately -40°F (-40°C).
    4. ⇒If the HVAC module does not display approximately -40°F (-40°C), test the ambient air temperature sensor signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC module.
  4. Ignition ON, perform an ambient air temperature sensor Instant Update to by pass filtering by simultaneously pressing the following switches on the HVAC control module:
    5. • LEFT TEMPERATURE UP
    • PASS ENABLE
    • REAR DEFOG ENABLE
  5. Ignition ON, install a 3-amp fused jumper wire between the ambient air temperature sensor signal circuit terminal A and the ambient air temperature sensor low reference circuit terminal B. Verify the HVAC module displays approximately 189.5°F (+87.5°C).
    6. ⇒If the HVAC module does not display approximately 189.5°F (87.5°C), test the ambient air temperature sensor signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC module.
  6. 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 HVAC module replacement, setup and programming