GM Code 66 Air Conditioning Pressure Switch Fault

CODE 66 - Air Conditioning Pressure Switch Fault

Trouble Code 66 indicates that A/C pressure sensor has determined that the A/C refrigerant system pressure is either too low (0 psi, .1 volt at sensor) or too high (450 PSI, 4.6 volts at sensor) for 5 seconds or more. If this code is present, the A/C compressor is disabled by the ECM.

Possible causes:

•  A/C system pressure is above or below calibrated values.
•  Faulty A/C Pressure Sensor or wiring.
•  Faulty ECM.