Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 66:

A/C Circuit:

CIRCUIT DESCRIPTION
The Air Conditioning (A/C) system uses an A/C refrigerant pressure sensor mounted in the high side of the A/C system to monitor A/C pressure for use by the Powertrain Control Module (PCM).

The PCM can use this information to turn "ON" the engine cooling fans when A/C refrigerant pressure is high. The PCM 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 PCM 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 PCM. The amount of signal returned to the PCM is then converted to a pressure value which can be displayed on the Tech 1 scanner.

DIAGNOSTIC TROUBLE CODE (DTC) 66 WILL SET WHEN
A/C refrigerant pressure sensor indicates A/C refrigerant pressure is below 55.2 kPa (8 psi) (which corresponds to 0.12 volt) for 10 seconds or A/C refrigerant pressure sensor indicates A/C refrigerant pressure is above 3089 kPa (448 psi) (which corresponds to 4.86 volts) for 10 seconds.

ACTION TAKEN (PCM DEFAULT)
DTC 66 will be stored in the PCM memory but will not turn "ON" the Malfunction Indicator Lamp (MIL), A/C operation will be disabled.

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Normal voltage is between 0.1 and 1.8 volt.

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 PCM.

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.