DTC 66

DTC 66 - A/C Pressure Sensor Circuit:

A/C Pressure Sensor Wiring Circuit:

Circuit Description:

The A/C 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 ECM to determine IAC valve position for idle speed control. The circuit consists of a 5 volts 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 0 to 468 psi. At 0 psi, the signal will be .1 volt, varying up to about 4.9 volts at 449 psi or above. The A/C compressor is disabled by the ECM if DTC 66 is present.

DTC 66 will set if:
^ A/C is requested "ON."
^ A/C pressure sensor signal does not indicate pressure between 0 psi (.1 volt) and 449 psi (4.9 volts) for 25 seconds.

DTC 66 does not illuminate the MIL (Service Engine Soon).

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step checks the voltage signal being received by the ECM from the A/C pressure sensor. The normal operating range is between .1 volt and 4.9 volts.
2. Checks to see if the high voltage signal is from a shorted sensor or a short to voltage in the circuit. Normally, disconnecting the sensor would cause the signal voltage go to near zero volts.
3. Checks to see 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 ECM.
4. This step checks to see if the low voltage signal was due to an open in the sensor circuit or the 5 volts reference circuit since the prior step eliminated the pressure switch.

Diagnostic Aids:

DTC 66 sets when signal voltage falls outside the normal possible range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in harness or poor connections. If OK, replace A/C pressure sensor. If DTC 66 re-sets, replace ECM.