JLG 3246ES Service Manual - Manual (Page 109)

SECTION 4 - HYDRAULICS
3121166 – JLG Lift – 4-7
Pump Motor Electrical Evaluation
Several basic electrical tests can be performed on the
Pump Motor. Failure of one of these evaluations is signif-
icant and may indicate that the device is physically dam-
aged.
Refer to Figure 7-2., Resistance Measurement. Make all
measurements with a voltmeter set to resistance scale
(Ohms). Disconnect the Main Battery Disconnect and all
pump motor cables during this analysis.
• Resistance < 5 Ohms between Motor Termninals.
The internal windings are very low impedance and
should appear to be a short-circuit for an ordinary
voltmeter (other tests can determine if the windings
are truly shorted). High resistance can signal worn
brushes, a faulty commutator, or open windings.
• Resistance > 1 MegaOhms between Motor Termi-
nals and Motor Housing. The internal windings
should be electrically isolated from the motor hous-
ing. Low resistance may be an indication of a broken
motor terminal, damaged brush, faulty commutator,
or burned winding.
Common Difficulties
The following difficulties can be examined using the JLG
Analyzer, a voltmeter, and simple hand tools. Unless
otherwise noted, the Control System shall be energized
in Ground Mode during testing. For a convenient
Ground Reference, place the black meter lead on the
negative post of the left battery in the left-side battery
compartment. The vehicle should be placed on a firm,
level surface for all analysis.
1. Open-Circuit between +B Terminal and Pump
Motor Positive Terminal
This issue will allow the vehicle to drive, but Lift Up
and Steer Functionality will be lost and the Pump
Motor will not operate. Under DIAGNOSTICS -
PUMP, the JLG Analyzer will show PUMP PWM
100% and PUMP CUR 0.0A when Lift Up is oper-
ated from Ground Mode.
As shown in the diagram, the voltage measured
between the Pump Motor Positive Terminal and
Ground Reference should be 24V. If it is not, exam-
ine the cable between the terminal and the Power
Module compartment. Inspect crimps for corro-
sion and ensure that bolted connections are tight.
Ensure that the cable is not crushed where it
passes between the frame side sheets and the cyl-
inder assembly.
2. Open-Circuit between Pump Motor Negative
Terminal and P Terminal
This issue will allow the vehicle to drive, but Lift Up
and Steer Functionality will be lost and the Pump
Motor will not operate. Under DIAGNOSTICS -
PUMP, the JLG Analyzer will show PUMP PWM
100% and PUMP CUR 0.0A when Lift Up is oper-
ated from Ground Mode.
After ensuring there is not an Open-Circuit
between the +B Terminal and Pump Motor Posi-
tive Terminal, check that the voltage measured
between the Pump Motor Negative Terminal and
Ground Reference is 24V. If not, examine the issues
within Open-Circuit Pump Motor. This voltage
should ramp to approximately 0V when Lift Up is
operated from Ground Mode. If not, examine the
cable between the terminal and the Power Module
compartment (P Terminal). Inspect crimps for cor-
rosion and ensure that bolted connections are
tight. Ensure that the cable is not crushed where it
passes between the frame side sheets and the cyl-
inder assembly.
3. Open-Circuit Pump Motor
This issue will allow the vehicle to drive, but Lift Up
and Steer Functionality will be lost and the Pump
Motor will not operate. Under DIAGNOSTICS -
PUMP, the JLG Analyzer will show PUMP PWM
100% and PUMP CUR 0.0A when Lift Up is oper-
ated from Ground Mode.
Pull the Main Battery Disconnect to completely
de-energize the Control System. Next, detach the
cable from Pump Motor Positive Terminal. Using a
voltmeter set for resistance measurement (Ohms),
ensure that the resistance between the Pump
Motor Positive and Negative Terminals is less than
2 Ohms. If not, examine the pump motor for worn
brushes or broken terminals. After examination,
re-connect the Pump Motor Positive Terminal and
the Main Battery Disconnect.
4. Short-Circuit between Pump Motor Positive
and Negative Terminals
This issue will allow the vehicle to drive, but Lift Up
and Steer Functionality will be lost and the Pump
Motor will not operate. Under DIAGNOSTICS -
PUMP, the JLG Analyzer will show an erratic read-
ing for PUMP PWM % and PUMP CUR will hover
around 150A when Lift Up is operated from
Ground Mode.
Pull the Main Battery Disconnect to completely
de-energize the Control System. Next, detach both
Pump Motor Terminals and insulate them inde-
pendently. Re-connect the Main Battery Discon-
nect and re-try Lift Up. If the same symptoms