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Cummins ISB CM550 (1990-94) Fault Code: 143-SN PID: 100 SPN: 100 FMI: 1 Oil Pressure Switch Circuit

Circuit Description
The oil pressure sensor is used by the engine control module (ECM) to monitor the lubricating
oil pressure. The ECM monitors the voltage on the signal pin and converts this to a pressure
value. The oil pressure value is used by the ECM for the engine protection system.

Component Location
The oil pressure sensor is located on the engine block, below and to the right of the ECM.

Shop Talk
1) Confirm that the oil pressure sensor supply voltage is between (+) 4.5 and 5.25-VDC at
the sensor.
2) Verify, with the driver, the engine speed at which the fault occurs. If the engine is being
operated at too low of a speed under load, the oil pressure can drop below the engine
protection limits.
3) Connect a manual gauge to monitor engine oil pressure and compare to the value in
your diagnostic tool.

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