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 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 (454 psi) or below .3 volt (7.5 psi) for 5 seconds or more. The A/C compressor clutch is disabled by the ECM if fault is present.

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 refrigerant pressure sensor.

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 volt reference circuit since the prior step eliminated the pressure sensor.

5. The 5 volt reference for the Throttle Position (TP) sensor connects to the same 5 volt power supply in the ECM. If the 5 volt reference circuit to TP sensor has a short to ground, the MAP sensor and A/C refrigerant pressure sensor 5 volt reference circuit will also have a short to ground because they connect to the same power supply in the ECM. A short to ground on either 5 volt reference circuit does not damage the ECM 5 volt power supply. When the short is repaired, the ECM 5 volt supply will return to normal.

DIAGNOSTIC AIDS:
At temperatures of -20 degrees Fahrenheit and below, the A/C pressure can drop below the .3 volt (7.5 psi) threshold. If this happens, the DTC 66 will set and disable the A/C system. Clear DTC 66 and check A/C pressure in a heated garage, if pressure is between .3 volt (7.5 psi) and 4.9 volts (454 psi), the A/C pressure transducer is functioning correctly.

DTC 66 sets when the 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. Refer to Heating and Air Conditioning.