Powertrain Controls - ECM/PCM

DTC 66 A/C Refrigerant Pressure Sensor Circuit:

A/C Pressure Switch / A/C Compressor Clutch Schematic:

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 Powertrain Control Module (PCM) to determine Idle Air Control (IAC) valve position for idle speed control. The PCM supplies a 5 volt reference and a ground. The signal voltage is proportional to the pressure. The sensor's range of operation is 0 to 450 psi. At 0 psi, the signal will be about 0.19 volt, varying up to about 4.9 volts at 450 psi or above.

DIAGNOSTIC TROUBLE CODE (DTC) 66 WILL SET WHEN
^ AC refrigerant pressure voltage is greater than 4.9 volts or less than 0.19 volt for 15 seconds.
OR
^ AC refrigerant pressure voltage is greater than 4.0 volts when A/C clutch is not requested.

ACTION TAKEN (PCM WILL DEFAULT TO)
A/C clutch is disabled, and the cooling fan will enable.

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

1. This checks the voltage signal being received by the PCM from the A/C refrigerant pressure sensor. The normal operating range is between 0.19 volt and 4.9 volts.
2. Checks 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 volt.
3. Checks 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.
4. This checks if the low voltage signal was due to an open in the sensor circuit or the 5 volt reference circuit since the prior step eliminated the A/C refrigerant pressure sensor.

DIAGNOSTIC AIDS
^ If DTC(s) 21, 22, or 34 are also set check CKT 416 for a short or open circuit.