JLG 601S ANSI Service Manual - Manual (Page 121)

SECTION 3 - CHASSIS & TURNTABLE
3120746 – JLG Lift – 3-81
The Engine Module is designed to maintain exhaust emis-
sion levels to government mandated standards while pro-
viding excellent operation and fuel efficiency. The Engine
Module monitors numerous engine functions via elec-
tronic sensors such as the throttle position (TP) sensor
and the heated oxygen sensor (HO2S).
ENGINE MODULE INPUTS/OUTPUTS
Inputs—Operating Conditions
• Engine Coolant Temperature
• Crankshaft Position
• Exhaust Oxygen Content
• Manifold Absolute Pressure
• Battery Voltage
• Throttle Position
• Fuel Pump Voltage
• Intake Air Temperature
• Camshaft Position
Outputs - System Controlled
• Fuel Control
• Idle Air Control
• Electric Fuel Pump
• Diagnostics:
- Malfunction Indicator Lamp
- Data Link Connector (DLC)
ENGINE MODULE SERVICE PRECAUTIONS
The Engine Module is designed to withstand normal cur-
rent draws associated with engine operation. When ser-
vicing the Engine Module, observe the following
guidelines:
• Do not overload any circuit.
• Do not probe wires for testing. This can cause a volt-
age drop that would be critical to the operation of the
Engine Module.
• When testing for opens and shorts, do not ground or
apply voltage to any of the Engine Module's circuits
unless instructed to do so.
• When measuring voltages, use only a digital voltmeter
with an input impedance of at least 10 megohms.
• Do not jump start with more than 12 volts. This could
cause damage to the electronic components.
• Do not employ any non-standard practices such as
charging the battery with an arc welder.
• Take proper precautions to avoid static damage to the
Engine Module. Refer to "Electrostatic Discharge Dam-
age" for more information.
THROTTLE POSITION (TP) SENSOR
The throttle position (TP) sensor is a potentiometer con-
nected to the throttle shaft on the throttle body which is
built into the electronic governor. The Engine Module
monitors the voltage on the signal line and calculates
throttle position. As the throttle valve angle is changed,
the TP sensor signal also changes. At a closed throttle
position, the output of the TP sensor is low. As the throttle
valve opens, the output increases so that at wide open
throttle (WOT), the output voltage should be above 4
volts.
The Engine Module calculates fuel delivery based on
throttle valve angle (operator demand). A broken or loose
TP sensor may cause intermittent bursts of fuel from an
injector and unstable idle because the Engine Module
thinks the throttle is moving. A hard failure in the TP sen-
sor 5-Volt reference or signal circuits for greater than 2
consecutive seconds will set either a DTC 12 or DTC 22. A
hard failure with the TP sensor ground circuit for more
than two consecutive seconds may set DTC 22. If either
DTC 12 or DTC 22 are set, the throttle will be forced to a
6% (idle) position.
USE OF CIRCUIT TESTING TOOLS
Do not use a test light to diagnose the engine electrical
systems unless specifically instructed by the diagnostic
procedures. A test light can put an excessive load on an
Engine Module circuit and result in component damage.
For volt-age measurements, use only a digital voltmeter
with an input impedance of at least 10 megohms.