Code 66, N Body, A/C Pressure Sensor: Notes

The A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. The ECM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from the ECM and returns an input signal to the ECM on a separate line. Low pressure (zero psi) will return a signal of about .1 volt. High pressure will return a signal of about 4.9 volts.

1. Checks voltage signal from A/C pressure sensor to ECM.
2. Checks to see if high 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 nearly zero volts.
3. Checks to see if low voltage signal is from the sensor or circuit. Jumpering the sensor signal circuit to 5-volt reference checks the circuit, connections and ECM.
4. Checks to see if the low voltage signal was due to an open in the sensor circuit or 5-volt reference circuit since the prior step eliminated the pressure sensor.