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 combination sensor is located in the back of the gear housing behind the injection pump on QSB
engines with the Bosch VP30 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.
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.