Cummins ISB CM550 (1990-94) Fault Code: 234 PID: 190 SPN: 190 FMI: 0 Engine Overspeed Circuit

Circuit Description
The engine speed sensor provides engine speed information to the electronic 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 No. 1 (and No. 6) is 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 No. 4 and No. 5.