Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 71:

A/C Clutch Circuit:

CIRCUIT DESCRIPTION
The A/C system uses an A/C evaporator temperature sensor mounted in the A/C evaporator core to monitor A/C temperature for use by the PCM. The Powertrain Control Module (PCM) uses this information to cycle the A/C compressor clutch "ON" and "OFF," so optimum cooling is attained. The A/C evaporator temperature sensor will also prevent A/C evaporator core freeze up. The PCM will disable the A/C compressor clutch whenever A/C evaporator temperature is below 2°C (36°F).

The A/C evaporator temperature sensor contains a two wire probe (thermistor) that is positioned in the center of the evaporator core. The two wire probe is part of the A/C evaporator temperature sensor interface module. The interface module works in conjunction with the PCM to determine A/C evaporator temperature.

DTC 71 WILL SET WHEN
A/C is requested, the PCM detects an open, short to ground, or a short to voltage in the A/C evaporator temperature circuits, and all conditions met for 3 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
Diagnostic Trouble Code (DTC) 71 will be stored in the PCM memory but will not turn on the Malfunction Indicator Lamp (MIL).

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

1. A/C evaporator temperature should be between these values.
2. With the A/C evaporator temperature sensor harness disconnected, normal voltage on CKT 732 is near 5 volts. If a short to voltage is suspected, reconnect sensor harness and backprobe terminal "B" of sensor harness using a DVOM. If 5 volts or more is indicated, then CKT 732 is shorted voltage.

DIAGNOSTIC AIDS
The A/C evaporator temperature sensor and harness is located under the passenger side instrument panel.

If A/C evaporator temperature sensor needs to be replace, refer to Heating and Air Conditioning/Service and Repair.