Cummins ISB CM550 (1990-94) Fault Code: 115VP44 PID: 190 SPN: 190 FMI: 2 Engine Speed Sensor (ESS) Circuit
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 machined 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 cylinder 1 and 6 are at top dead center.
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 fuel system.
This fault code will also cause a fuel derate. This could be the cause of a low-power complaint. Also, this fault code can cause starting problems in cold weather.
ISB and QSB engines with the fuel pump system use separate sensors for engine speed and position.