Powertrain Controls - ECM/PCM

Code 66 Chart:

A/C Wiring Circuit:

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 450 psi. At 0 psi the signal will be about 0.1 volt, varying up to about 4.9 volts at 450 psi or above. Code 66 sets if the voltage falls outside of calibrated minimum and maximum values for 5 seconds or more. The A/C compressor is disabled by the ECM if Code 66 is present.

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 0.128V 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 make a normal circuit 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 sensor.

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.