DTC 66

DTC 66 A/C Refrigerant Pressure Sensor Circuit:

A/C System Wiring Diagram:

Circuit Description

The A/C system uses an A/C refrigerant pressure sensor mounted in the high side of the A/C system to monitor A/C refrigerant pressure.

The ECM uses this information to turn "ON" the engine cooling fans when A/C pressure is high. The ECM can prevent compressor damage by disabling the compressor clutch if head pressure gets too high.

The A/C refrigerant pressure sensor operates much like other 3-wire sensors. A 5 volt reference is supplied to the sensor and returned to the ECM on the signal line. As the A/C refrigerant pressure increases or decreases, the resistance of the sensor changes and varies the amount of signal returning to the ECM. The amount of signal returned to the ECM is then converted to a pressure value which can be displayed on the scanner. A DTC 66 fault will store a DTC in the ECM memory but will not turn "ON" the MIL (Service Engine Soon) light.

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

1. DTC 66 will set if:

- A/C refrigerant pressure sensor indicates A/C refrigerant pressure is below psi -8 psi (0.12 volt) for 10 seconds.

OR

- A/C refrigerant pressure sensor indicates A/C refrigerant pressure is above 448 psi (4.86 volts) for 10 seconds.

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 range of the sensor and is not due to a refrigerant system problem. If problem is intermittent, check for opens or shorts in the harness, or poor connections.