DTC 04

CIRCUIT DESCRIPTION
The inside air temperature sensor is a thermistor used to control the signal voltage at the H-A/C control. The H-A/C control supplies a reference voltage (about 5 volts) on CKT 734 to the sensor When the inside air temperature is cold, the thermistor resistance is high; therefore, the H-A/C control will receive a high signal voltage input. If the inside air temperature is hot, the thermistor resistance is low; therefore the H-A/C control will receive a low signal voltage input.

DTC WILL SET WHEN
With ignition in "RUN," the H-A/C control will detect this fault anytime that CKT 734 stays at or near 0 volts.

ACTION TAKEN
DTC 04 will set in the H-A/C control. With DTC 03 present, the H-A/C control will use a default value of 128 or 24°C (75°F). This can be seen by displaying parameter "-28" for the inside air temperature sensor.

DTC WILL CLEAR WHEN
This fault will clear as soon as the fault has been repaired. The system will then return to normal operation.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This test checks for HVAC DTC(s) and should clear any intermittent DTC(s).
2. This test checks resistance of inside air temperature sensor.
3. This test checks for a ground in CKT 734.

DIAGNOSTIC AIDS
Visually inspect sensor thermistor element for broken wires or contamination by removing right-hand instrument panel molding.