GM Service Manual Online
For 1990-2009 cars only

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

Signal Performance

Ambient Air Temperature Sensor Signal

B0158 02

B0158 05

B0158 05

1

1. Air Temperature Malfunction

Circuit/System Description

Air Temperature Sensor

The air temperature sensors are a 2-wire negative temperature co-efficient thermistor.

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +101°C (-40 to +215°F). The sensor signal varies between 0-5 volts. The input of the duct air temperature sensors are different from the ambient and inside air temperature sensors. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease. If the HVAC control module or auxiliary HVAC control module detects a malfunctioning sensor, then the control module software will use a defaulted air temperature value. The default value for the ambient air temperature sensor will be displayed on the scan tool.

Diagnostic Aids

Ambient Air Temperature Display Update

Condition

Display

Using Scan Tool Special Function

Updates temperature display instantly

When the HVAC module MODE, FRONT DEFROST, and REAR DEFROST buttons are pressed simultaneously.

Updates temperature display instantly

At start up with the engine off less than 2 hours

Displays last stored temperature unless temperature has decreased. The outside air temperature reading is always instantly updated if ambient air temperature has decreased.

At start up with the engine off more than 2 hours

Displays actual outside temperature

Vehicle speed above 32 km/h (20 mph) for a minimum of 80 seconds

Updates temperature display at a slow filtered rate

Vehicle speed above 72 km/h (45 mph)

Displays actual outside temperature

Sensor ambient temperature reading is less than the last displayed value

Displays actual outside temperature

When the ambient air decreases

Updates temperature display rapidly

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

    •  Air Delivery Description and Operation
    •  Air Temperature Description and Operation

Electrical Information Reference

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

Scan Tool Reference

Control Module References for scan tool information

Ambient Air Temperature Sensor Circuit Malfunction

  1. Ignition OFF, disconnect the harness connector at the ambient temperature sensor.
  2. Test for less than 1 ohm of resistance between the low reference circuit terminal B and ground.
  3. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  4. Ignition ON, verify the appropriate scan tool Temp Sensor Voltage parameter is greater than 4.9 volts or 250 counts.
  5. If less than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module.
  6. Install a 3-amp fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool Temp Sensor Voltage parameter is less than 0.1 volt or 5 counts.
  7. If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  8. If all circuits test normal, test or replace the appropriate temperature sensor.

Component Testing

  1. Ignition OFF, disconnect the harness connector at the appropriate temperature sensor.
  2. Test for the appropriate resistance between the signal terminal A and the low reference terminal B.Refer to Sensor Resistance Table for resistance values.
If not within the specified range, replace the appropriate sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Ambient Air Temperature Sensor Replacement