Powertrain Controls - ECM/PCM

Code Chart 66:

A/C Refrigerant Pressure Sensor Wiring Circuit:

Circuit Description:
The A/C refrigerant pressure sensor responds to changes in A/C refrigerant system high side pressure. This input indicates how much load the A/C compressor is putting on the engine and is one of the factors used by the ECM to determine IAC valve position for idle speed control. The circuit consists of a 5 volt reference and a ground, both provided by the ECM and a signal line to the ECM. The signal is a voltage which is proportional to the pressure. The sensors range of operation is 0 to 454 psi. At 0 psi, the signal will be about .1 volt, varying up to about 4.9 volts at 454 psi or above.

DTC 66 Will Set When:
^ The signal voltage is above 4.9 volts (454 psi) or below .1 volt (0 psi) for 5 seconds or more.

Action Taken (ECM will default to): Malfunction Indicator Lamp (MIL) DOES NOT illuminate. A/C compressor clutch is disabled.

DTC Chart Test Description: Number(s) below refer to circled numbers on the diagnostic chart
1. This step checks the voltage signal being received by the ECM from the A/C refrigerant pressure sensor. The normal operating range is between .1 volt and 4.9 volts.
2. Checks to see if the high voltage signal is from a shorted sensor or a short to voltage in the circuit. Normally, disconnecting the sensor would make a normal circuit go to near zero volts.
3. Checks to see if low voltage signal is from the sensor or the circuit. Jumpering the sensor signal CKT 380 to 5 volts, checks the circuit, connections, and ECM.
4. This step checks to see if the low voltage signal was due to an open in the sensor circuit or the 5 volts reference circuit since the prior step eliminated the pressure sensor.

Diagnostic Aids: DTC 66 sets when the signal voltage falls outside the normal possible range of the sensor. If signal voltage is greater than .1 volt, but less than 3 volt, there could be a low refrigerant pressure problem with the A/C system. Refer to "A/C" section.