Dtc 643- 5 volt external high voltage, Dtc 643- 5 volt external high voltage -194, Diagnostic aids – JLG 450A_AJ Series II Service Manual User Manual
Page 244
SECTION 3 - CHASSIS & TURNTABLE
3-194
– JLG Lift –
3121180
DTC 643- 5 Volt External High Voltage
• 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 devices are active and put devices in a
low or no power state based on current operating condi-
tion of 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 5-volt ECM output while cycling key on and
engine stopped. Verify output is lower than fault thresh-
olds configured in diagnostic calibration.
• Inspect 5-Volt output circuit in wire harness and look
for shorts to ground or other harness circuits.
• Disconnect each device powered by the ECM 5-volt
output one-at-a-time. Powered devices may include
the throttle actuator, smart sensors, smart actuators,
etc. After disconnecting device, observe system fault
and determine if fault has cleared. If fault clears, trou-
bleshoot disconnected device for failures.
• With all 5-volt powered devices disconnected, look for a
change in fault state, measure the ECM 5-volt output
and verify it is within acceptable limits.
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Electronic Throttle
Actuator w/Serial
Position Feedback
2
16
13
12
1
5V_ext
Vs=+5 VDC
5V_rtn
TPS1
TPS SER +
+
-
Motor
DBW-
DBW+
ECM
H-Bridge
19
TPS SER -
Serial
xmitter