JLG 450A_AJ Series II Service Manual - Manual (Page 225)

SECTION 3 - CHASSIS & TURNTABLE
3121180 – JLG Lift – 3-175
DTC 337- Loss of Crank Input Signal
• Crankshaft Position sensor.
• Check Condition- Key On, Engine On.
• Fault Condition- Loss of crankshaft position signal
while valid camshaft position signals continue for x
number of cam pulses as defined in the diagnostic cal-
ibration.
• Corrective Action(s)- Illuminate MIL and/or sound audi-
ble warning or illuminate secondary warning lamp.
• Emissions related fault.
The crankshaft position sensor is a magnetic sensor (vari-
able reluctant/magnetic pick-up or Hall effect) installed in
the engine block adjacent to a ¡§coded¡¨ trigger wheel
located on the crankshaft. The sensor-trigger wheel com-
bination is used to determine crankshaft position (with
respect to TDC cylinder #1 compression) and rotational
engine speed. Determination of the crankshaft position
and speed is necessary to properly activate the ignition,
fuel injection, and throttle governing systems for precise
engine control.
The ECM must see a valid crankshaft position signal while
running. If no signal is present while x cam pulses con-
tinue, the fault will set. The engine typically stalls or dies
as a result of this fault condition due to lack of crankshaft
speed input, resulting in loss of ignition timing control.
Diagnostic Aids
• Check crankshaft position sensor is securely con-
nected to harness.
• Check crankshaft position sensor is securely installed
in engine block.
• Check crankshaft position sensor circuit wiring for
open circuit.