DTC 03

CIRCUIT DESCRIPTION

The outside air temperature sensor is a thermistor that provides a signal voltage to the control assembly microprocessor (15).

The microprocessor (15) supplies a reference voltage (about 5 volts) on CKT 735 to the sensor. When the outside air temperature is cold, the thermistor resistance is high; therefore, the microprocessor (15) will receive a high signal voltage input. If the outside air temperature is high, the thermistor resistance is low; therefore the microprocessor (15) will receive a low signal voltage input.

TEST DESCRIPTION

The following numbers refer to circled numbers on the diagnostic chart.

1. This test will determine if the microprocessor (15) has defaulted to a default value of 128 which represents 10°C (50°F) and Code 03 has set. Code 03 will set if a high resistance (open) is present for more than 1.6 seconds.

2. This test will determine if the outside air temperature sensor is within its correct range. The resistance varies with temperature, so the Diagnostic Aid Correction Chart must be used if outside temperature is not 16°C (59°F).

3. Pointer -03 will also display counts from outside air temperature sensor. The count should be close to the specified resistance value count for the outside air temperature as shown in the Diagnostic Aid Correction Chart. If not, an open or short to ground is the most likely cause.

4. This test will determine if the malfunction is intermittent or if an open is present in the 5-volt reference voltage to the sensor. Terminal C7 should be checked. If no voltage is present, replace the microprocessor (15).

DIAGNOSTIC AIDS

if Code 03 is not displayed in parameter -00 or no malfunction is found through Step 4, pointer - 03 using scan tool while checking for opens and grounds in harness by moving harness. If no opens (248 counts) can be found, monitor sensor at maximum cold and hot interior temperatures while driving vehicle. Replace sensor if out of parameter. If sensor is in parameter, replace microprocessor (15).