Manual

Electronic Power Steering
27
Troubleshooting the EPS (without the 725-05419 EPS tester)
The first step in troubleshooting the EPS system is to
understand how it works.
See Figure 3B.4.
• A constant 12 volts is supplied by the battery
through a 40 amp fuse in the fuse box.
• The EPS is grounded through the green wire.
• The EPS senses the ignition pulses from the igni-
tion module primary windings through the yellow
wire with a white trace.
NOTE: On tractors with Kohler engines with a Digital
Spark Advance (DSA) ignition, A diode is installed
to protect the ignition module from any stray volt
-
age that may come from the engine shut down cir-
cuits. A white wire carries a clean spark signal to
the EPS to turn it on.
See Figure 3B.5.
• Once the EPS determines that the engine is run-
ning (by sensing the ignition pulses from the igni-
tion coil) it will turn on.
• The EPS will power the EPS motor as it senses
input from the steering wheel.
To troubleshoot the EPS assembly:
1 Check the 40 amp fuse in the fuse box.
See Figure 3B.6.
NOTE: If the fuse is blown, check for a short in the red
wire that goes to the EPS assembly before replac
-
ing the fuse.
The technician needs to determine if there is a mechan-
ical bind in the steering system or an EPS issue. The easi-
est way to rule out a binding steering system is to:
2. Remove the steering pinion gear by following the
procedures described in Chapter 3: Steering.
3. Start the engine.
4. Operate the steering wheel.
• If the steering wheel now moves freely, the issue is
downstream of the pinion gear. The most likely
suspect would be axles frozen to the pivot bar.
• If the steering wheel is still hard to operate, isolate
the problem to either the EPS assembly or the cir
-
cuits that go to the EPS assembly.
NOTE: To protect the EPS module, it will turn off if the
steering input is held at a hard stop for more than 2
seconds. The EPS will turn back on once the input
is released from the hard stop.
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Figure 3B.4
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Figure 3B.5
Figure 3B.6
40 amp fuse