Cummins ISB CM550 (1990-94) Fault Code: 123 PID: 102 SPN: 102 FMI: 4 Intake Manifold Pressure Sensor Circuit

Circuit Description
The intake manifold pressure sensor monitors intake manifold pressure and passes
information to the electronic control module (ECM) through the sensor harness. If the intake
manifold pressure becomes too high, it will cause a derate condition.

Component Location
The intake manifold pressure sensor is located on the rear of the intake air manifold in the
second port on the side of the head to the right of the fuel filter.

Shop Talk
1) Determine if engine is being overfueled.
2) Confirm that the correct intake manifold pressure sensor part number is being used.
3) Confirm that the correct turbocharger is being used.
4) If it is suspected that cold intake air is the cause of the high intake manifold pressure, test
the engine with warm intake air.
5) Check for high restriction in the intake air manifold due to a shutdown device in the
manifold (if the vehicle is equipped with one). Do not remove this device. If the engine is
operated in a flammable atmosphere, the device is an essential safety feature.

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