Powertrain Controls - ECM/PCM

DTC 66 Chart:

A/C 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 PCM to determine IAC valve position for idle speed control, and engine cooling fan operation. The circuit consists of a 5 volt reference and a ground, both provided by the PCM, and a signal line to the PCM. The signal is a voltage which is proportional to the pressure. The sensor's range of operation is 0 to 450 psi. At 0 psi, the signal will be about .1 volt, varying up to about 4.9 volts at 450 psi or above. DTC 66 sets if the voltage is less than .1 volt (approximately less than 0 psi) for 5 seconds or more. The A/C compressor is disabled by the PCM if DTC 66 is present or if pressure is above or below calibrated values.

DTC 66 Will Set When:
The signal voltage sensed at terminal "AS" is below .1 volt for 5 seconds when A/C is selected "ON" and the engine is running.

Action Taken (PCM will default to):
The MIL will not become illuminated, the A/C compressor will be 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 66.

DTC 66 Will Clear When:
A current DTC 66 will clear when the refrigerant pressure sensor voltage rises above the calibrated low pressure threshold. A history DTC 66 will clear after 50 consecutive ignition key cycles without a current DTC 66 being stored.

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

1. This step checks the voltage signal being received by the PCM from the A/C refrigerant pressure sensor.

2. 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 PCM.

3. This step checks to see if the low signal voltage was due to an open in the sensor circuit or the 5 volt reference circuit since the previous step eliminated the pressure sensor.

Diagnostic Aids:
DTC 66 sets when signal voltage falls outside the normal possible range of the sensor and is not due to a refrigerant system problem. If the problem is intermittent, check for opens or shorts in harness or poor connections.