Powertrain Controls - ECM/PCM

DTC 71 A/C Evaporative Temperature Sensor:

A/C Evaporative Temperature Sensor Wiring Diagram:

Circuit Description:

Integral to the A/C system is the A/C evaporator temperature sensor. This sensor is mounted to the evaporator which is located within the I/P. The ECM receives a voltage signal inversely proportional to the temperature at the evaporator coils. As the evaporator temperature increases or decreases, the resistance of the sensor changes and varies the voltage signal to the ECM. This voltage is converted to a temperature value by the ECM and can then be displayed in degrees by the scanner. A DTC 71 fault will be stored in the ECM when evaporator temperature is less than -7°C but will not illuminate the Malfunction Indicator Lamp (MIL) "Service Engine Light Soon."

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

1. DTC 71 will set if:

^ A/C evaporator temperature sensor indicates less than -7°C (19°F).
^ Time since start is 5 seconds.

Diagnostic Aids:

DTC 71 sets when signal voltage falls outside the normal range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in the harness, or poor connections. A sensor which has backed out of the evaporator coil bracket will also set a false DTC.