Service Manual

SECTION 3 - CHASSIS & TURNTABLE
3-64 – JLG Lift – 3121202
The ECM/EPM is designed to maintain exhaust emission
levels to government mandated standards while providing
excellent operation and fuel efficiency. The ECM/EPM
monitors numerous engine functions via electronic sen-
sors such as the throttle position (TP) sensor and the
heated oxygen sensor (HO2S).
ECM/EPM 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)
ECM/EPM SERVICE PRECAUTIONS
The ECM/EPM is designed to withstand normal current
draws associated with engine operation. When servicing
the ECM/EPM, 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
ECM/EPM.
• When testing for opens and shorts, do not ground or
apply voltage to any of the ECM/EPM'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
ECM/EPM. Refer to "Electrostatic Discharge Damage"
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 ECM/EPM monitors
the voltage on the signal line and calculates throttle posi-
tion. As the throttle valve angle is changed, the TP sensor
signal also changes. At a closed throttle position, the out-
put 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 ECM/EPM calculates fuel delivery based on throttle
valve angle (operator demand). A broken or loose TP sen-
sor may cause intermittent bursts of fuel from an injector
and unstable idle because the ECM/EPM thinks the throt-
tle is moving. A hard failure in the TP sensor 5-Volt refer-
ence 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 con-
secutive seconds may set DTC 22. If either DTC 12 or DTC
22 are set, the throttle will be forced to a 6% (idle) posi-
tion.
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
ECM circuit and result in component damage. For volt-
age measurements, use only a digital voltmeter with an
input impedance of at least 10 megohms.