Powertrain Controls - ECM/PCM

DTC 71 Chart:

A/C Circuit:

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 PCM 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 PCM. This voltage is converted to a temperature valve by the PCM and can then be displayed in degrees by the Tech 1. A DTC 71 fault will be stored in the PCM when evaporator temperature is less than -7°C but will not illuminate the Malfunction Indicator Lamp (MIL) "Service Engine Soon."

DTC 71 Will Set When:
A/C evaporator temperature indicates less than -7°C (19°F) for 5 seconds.

Action Taken (PCM will default to):
The MIL will not become illuminated, the A/C compressor will become disabled, the cooling fan will not be enabled unless A/C had been requested first and the vehicle speed is above 35 mph with a current DTC 71.

DTC 71 Will Clear When:
A current DTC 71 will clear when the signal voltage falls within the calibrated threshold of the A/C evaporator temperature sensor. A history DTC 71 will clear after 50 consecutive ignition key cycles without a current DTC 71 being stored.

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

1. This test is a verification that the DTC is not intermittent.

Diagnostic Aids:
If a 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.