DTC 66

Code Chart 66:

A/C 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 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 0 to 454 psi. At 0 psi, the signal will be about .1 volt, varying up to about 4.9 volts at 454 psi or above. DTC 66 sets if the voltage is above 4.9 volts or below .1 volt for 5 seconds or more. The A/C compressor is disabled by the ECM if the fault is presently occurring or if pressure is above or below calibrated values.

TEST DESCRIPTION: Numbers below refer to circled numbers 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 make a normal circuit 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 sensor.

DIAGNOSTIC AIDS:
DTC 66 sets when signal voltage falls outside the normal possible range of the sensor. If signal voltage is greater than .1 volt, but less than .3 volt, there could be a low refrigerant pressure problem with the A/C system.