Cummins ISB CM550 (1990-94) Fault Code: 284 PID: 190 SPN: 190 FMI: 4 Engine Speed Sensor Supply

Circuit Description
The engine speed sensor provides engine speed information to the engine control module (ECM). The sensor must be powered up by +5 VDC to operate. The sensor generates its signals by sensing the movement of target teeth cast into a tone wheel that is mounted to the crankshaft. The tone wheel has 35 teeth and a gap where the 36th tooth would be placed. This missing tooth indicates that cylinder 1 and 6 are at top dead center.

Component Location
The engine speed sensor is located on the intake side of the engine block, at crankshaft level, between cylinders 4 and 5 on ISB and QSB5.9 engine with the Bosch fuelpump system. The sensor is located in the back of the gear housing behind the injection pump on QSB engines with the Bosch VP30 fuel system.

Shop Talk
QSB engines with the Bosch VP30 fuel system use only an engine speed sensor located in the gear housing below the injection pump, that reads off a tone
wheel bolted to the camshaft gear. This is a combination sensor that provides both speed and position. ISB and QSB engines with the Bosch fuelpump
system use separate sensors for engine speed and position.