Code 66 - A/C Pressure Sensor (3.4L "W" Body): Notes
WARNING: This page is about a different car, the 1993 Pontiac Grand Prix, 1993 Pontiac Firebird, 1993 Oldsmobile Cutlass Supreme, 1993 Chevrolet Lumina, and 1993 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
A/C pressure sensor responds to changes in A/C refrigerant system high side pressure. ECM uses A/C compressor load input to determine engine idle speed. Sensor uses a 5-volt reference signal from ECM and returns an input signal to 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 4.6 volts.
NOTE:
Test numbers refer to numbers on diagnostic chart.
- Checks voltage signal from A/C pressure sensor to ECM.
- Checks to see if high signal is from a shorted sensor or a short to voltage in circuit. Normally, disconnecting sensor would make a normal circuit go to nearly zero volts.
- Checks to see if low voltage signal is from sensor or circuit. Jumpering sensor signal circuit to 5-volt reference checks circuit, connections and ECM.
- Checks to see if low voltage signal was due to an open in sensor circuit; previous step eliminated pressure sensor as a possible cause.