Powertrain Controls - ECM/PCM

Code 66 Diagnostic Chart:

A/C System Wiring.:

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 Powertrain Control Module (PCM) to determine IAC valve position for idle speed control. The circuit consists of a 5 volt reference and a ground, both provided by the PCM, and a signal line to the PCM. 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.

DTC 66 WILL SET WHEN
^ A/C pressure sensor signal voltage greater than 4.9 volts or less than 0.28 volt for 15 seconds.

OR

^ A/C pressure sensor signal voltage greater than 4.0 volts when A/C clutch is not requested.

ACTION TAKEN (PCM WILL DEFAULT TO)
A/C clutch is disabled.

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 PCM from the A/C refrigerant pressure sensor. The normal operating range is between 0.28 volt and 4.9 volts.
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 volt reference circuit since the prior step eliminated the A/C refrigerant pressure sensor.

DIAGNOSTIC AIDS
DTC 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 refrigerant pressure sensor. if DTC 66 resets, replace PCM.

NOTE: Non-A/C Program DTC 66 will set on a non-A/C equipped vehicle, if CKT 451 to terminal "PB5" is open or shorted to B+.