Powertrain Controls - ECM/PCM

Code 66 Chart:

Code 66 Wiring Diagram:

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 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 468 psi.

At 0 psi the the signal will be 0.1 volt varying up to about 4.9 volts at 449 psi or above. The A/C compressor is disabled by the ECM if Code 66 is present.

Code 66 sets if:

^ The A/C is requested "ON."

^ A/C pressure sensor signal does not indicate pressure between 0 psi (0.1 volt) and 449 psi (4.9 volts) for 25 seconds.

^ Code 66 does not illuminate the "Service Engine Soon" light.

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 0.1V and 4.9V.

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 cause the signal voltage to 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 switch.


DIAGNOSTIC AIDS:

Code 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 Code 66 re-sets, replace ECM.