DTC 66

Code Chart 66:

A/C Circuit:

CIRCUIT DESCRIPTION:
The A/C refrigerant 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 450 psi At 0 psi, the signal will be about .1 volt, varying up to about 4.9 volts at 450 psi or above. DTC 66 sets if the voltage is above 4.9 volts or below 1 volt 5 seconds or more. The A/C compressor is disabled by the ECM if DTC 66 is present, or if pressure is above or below calibrated values described in "A/C Compressor Clutch Circuit Diagnosis" in CHART C-10.

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 make a normal circuit go to near zero volt.

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 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 resets, replace ECM.