Powertrain Controls - ECM/PCM

Trouble Code 66 Chart:

A/C Refrigerant Pressure Sensor:

CIRCUIT DESCRIPTION
The A/C refrigerant pressure sensor is located in the high side of the A/C cooling system and signals the Powertrain Control Module (PCM) of refrigerant pressure changes. This input indicates how much load the A/C compressor is putting on the engine. The PCM uses this input to determine Idle Air Control (IAC) valve position for idle speed control. This 3 wire sensor has a 5 volt reference input, a signal line and a ground.
When pressure is low, a low signal voltage is sensed at the PCM. As pressure rises, the voltage increases at PCM terminal "A5" which is translated by the PCM into rising pressure. If the signal voltage remains below a calibrated value, a Diagnostic Trouble Code (DTC) 66 is set which indicates a sensor or circuit failure.

DTC 66 WILL SET WHEN
The signal voltage sensed at terminal "A5" is below 0.1 volt for 5 seconds when A/C is selected "ON" and the engine is running.

ACTION TAKEN (PCM) WILL DEFAULT TO
The MIL will not become illuminated and the A/C compressor will be disabled.

DTC 66 WILL CLEAR WHEN
A current DTC 66 will clear when the refrigerant pressure sensor voltage rises above the calibrated low pressure threshold. A History DTC 66 will clear after 50 consecutive ignition key cycles without a current DTC 66 being stored.

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

1. This step checks the voltage signal being received by the PCM from the A/C pressure sensor.
2. Checks to see if low voltage signal is from the sensor or the circuit. Jumpering the sensor signal circuit 380 to 5 volts checks the circuit, connections, and PCM.
3. This step checks to see if the low signal voltage was due to an open in the sensor circuit or the 5 volts reference circuit since the previous step eliminated the 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 the problem is intermittent, check for opens or shorts in harness or poor connections.