DTC 03

Circuit Description:

The outside air temperature sensor is a thermistor used to control the signal voltage to the heater and A/C programmer.

The programmer supplies a voltage (about 5 volts/reference) on CKT 735 to the sensor. When the ambient (outside) air temperature is cold, the sensor (thermistor) resistance is high, therefore, the programmer will see a high signal voltage. If the ambient (outside) air temperature is high, the sensor (thermistor) resistance is low, therefore, the heater and A/C programmer will see a low voltage.

Test Description:

Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test will determine if the sensor is shorted or open internally. If the temperature/resistance relationship is not within the specified range, the sensor should be replaced.
2. This test will determine if there is an open or short in the entire circuit. If no open or short is present and the temperature/resistance relationships are within specifications, the HVAC programmer should be replaced.

Diagnostic Aids:

If resistance readings are within range at the sensor, but are out of range when checked at the HVAC programmer, check all connections in between for water intrusion or corrosion.

After performing Steps 1 and 2, if no problem is found, check for an
intermittent open or short while moving the wire harness and monitoring
resistance at HVAC programmer harness terminals "D16" and "C16".