JLG 3246ES Service Manual - Manual (Page 73)

SECTION 3 - CHASSIS & SCISSOR ARMS
3121166 – JLG Lift – 3-37
Common Traction System Difficulties
1. Short-Circuit Motor Armature
This issue will allow the vehicle to drive very slowly
or not at all. Rapid motor overheating (one motor)
will result.
This situation can be detected by elevating the
vehicle's front wheels and engaging drive (plat-
form stowed). Under DIAGNOSTICS - TRACTION,
the JLG Analyzer's ARM CUR display (Armature
Current Reading) will exceed 120A. The FLD CUR
display (Field Current Reading) will hover around
40A. Neither wheel will rotate at normal speed,
but it will be possible to rotate the drive wheel by
hand. The Power Module's self-diagnostics cannot
detect this fault since the situation appears identi-
cal to climbing a steep grade.
To find the source of the difficulty, pull the Main
Battery Disconnect and disconnect the Armature
Wiring (heavy red and black conductors) from the
suspected drive motor leading to the Power Mod-
ule's M1 and M2 Terminals. Re-test the traction
function. If the remaining drive motor is able to
reach full speed (and Armature Current is less than
50A), the drive motor that has been disconnected
is fault. Investigate for crushed and burned cables.
Note if the drive motor smells burned.
2. Short-Circuit Brake Release
This issue will not allow the vehicle to drive. Rapid
motor overheating (both motors) will result. Con-
tinued attempts to drive the vehicle may result in
armature damage.
This situation can be detected by elevating the
vehicle's front wheels and engaging drive (plat-
form stowed). Under DIAGNOSTICS - TRACTION,
the JLG Analyzer's ARM CUR display (Armature
Current Reading) will exceed 120A. The FLD CUR
display (Field Current Reading) will hover around
40A. Neither wheel will rotate, and it will be
impossible to rotate either drive wheel by hand.
The Ground Module cannot detect this fault dur-
ing power-up or self-test since energizing the
brakes could pose a hazard. However, it may
detect this issue during Drive (investigate using
JLG Analyzer).
To find the source of the difficulty, remove the rear
cover from either drive motor. Insert voltmeter
leads into the white connector leading to the
brake solenoid (yellow and brown wires) and
attempt to drive (Platform Mode). The Ground
Module will apply approximately 24V to the brake
release solenoids (wired in parallel) during drive,
but will reduce this voltage in the event of a short-
circuit. If this voltage is improper (less than 8V),
investigate using resistance measurement (refer to
Drive Motor Electrical Evaluation). Suspect dam-
aged cabling, burned cabling, or faulty brake
release solenoids. Trace the brake release cabling
from the Power Module Compartment to the
Ground Module Connector J1-24.
3. Open-Circuit Brake Release
This issue will not allow the vehicle to drive. Rapid
motor overheating (both motors) will result. Con-
tinued attempts to drive the vehicle may result in
armature damage.
This situation can be detected by elevating the
vehicle's front wheels and engaging drive (plat-
form stowed). Under DIAGNOSTICS - TRACTION,
the JLG Analyzer's ARM CUR display (Armature
Current Reading) will exceed 120A. The FLD CUR
display (Field Current Reading) will hover around
40A. It is possible that one wheel may rotate, or
neither may rotate (depending on the location of
the open-circuit). Listen for the brake release sole-
noid when activating drive. The Ground Module
cannot detect this fault during power-up or self-
test since energizing the brakes could pose a haz-
ard. However, it may detect this issue during Drive
(investigate using JLG Analyzer).
If one wheel rotates, the open-circuit is located in
the wiring for that specific drive motor (Power
Module compartment or Drive Motor Cable).
Investigate for improper crimps, unlatched con-
nectors, damaged cables, or open brake release
solenoids (refer to Drive Motor Electrical Evalua-
tion).
If neither wheel rotates, the open-circuit is located
in the wiring between the Power Module compart-
ment and Ground Module. Using a voltmeter, mea-
sure the brake release voltage on either brake
connector in the Power Module compartment dur-
ing drive (should be approximately 24V). Investi-
gate for improper crimps, unlatched connectors,
damaged harnessing, or a faulty Ground Module.
As an alternative, insert a short piece of wire with a
Deutsch Female Crimp directly into Ground Mod-
ule's J1-24 and measure voltage as a diagnostic
measure (eject vehicle harness from that pin).