Oshkosh JLG 400S, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3120895 – JLG Lift – 3-189
• Engine Control Module
• Check Condition- Key on
• Fault Condition- ECM 5-volt output is above the
acceptable limit
• Corrective Action(s)- Illuminate MIL and/or sound audi-
ble warning or illuminate secondary warning lamp
• Non-emissions related fault
The ECM supplies 5-volt power to sensors, switches, and
actuators external to the ECM. By supplying the power to
these devices, the ECM can accurately measure their out-
put relative to its own ground reference. The ECM can
also control when the devices are active and put the
devices in a low or no power state based on the current
operating condition of the engine or vehicle.
If this fault sets, something other than the ECM is drawing
the 5-volt power output of the ECM above an acceptable
threshold. This may be due to a short in the wire harness,
malfunctioning device, or failure of the ECM power output
circuitry.
Diagnostic Aids
• Measure the 5-volt output of the ECM while cycling the
key on and the engine stopped. Verify that the output is
lower than the fault thresholds configured in the diag-
nostic calibration.
• Inspect the 5-Volt output circuit in the wire harness and
look for shorts to ground or other harness circuits.
• Disconnect each device powered by the 5-volt output
of the ECM one-at-a-time. Powered devices may
include the throttle actuator, smart sensors, smart actu-
ators, etc. After disconnecting device, observe the sys-
tem fault and determine if the fault has cleared. If the
fault clears, troubleshoot the disconnected device for
failures.
• With all 5-volt powered devices disconnected, look for a
change in the fault state and measure the 5-volt output
of the ECM and verify it is within acceptable limits.