Code 66 - Low A/C Charge (3.4L "F" Body): Notes

The A/C refrigerant pressure sensor responds to changes in A/C refrigerant system high side pressure. Input indicates how much load 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, and engine cooling fan operation. 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 sensor's range of operation is zero to 450 psi. At zero psi, the signal will be about .1 volt, varying up to about 4.9 volts at 450 psi or above. Code 66 sets if the voltage is less than one volt (approximately less than zero psi) for 5 seconds or more. The A/C compressor is disabled by the ECM if Code 66 is present or if pressure is greater than or less than calibrated values.

1. This step checks the voltage signal being received by the ECM 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 circuit to 5 volts checks the circuit, connections and ECM.
3. This step checks to see if the low voltage signal was due to an open in the sensor signal circuit or the 5-volt reference circuit, since the proper step eliminated the pressure sensor.