Dtc 643- 5 volt external high voltage, Dtc 643- 5 volt external high voltage -149, Diagnostic aids – JLG 450A_AJ Series II Service Manual User Manual
Page 189
SECTION 3 - CHASSIS & TURNTABLE
3121290
– JLG Lift –
3-149
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 audible
warning or illuminate secondary warning lamp.
• Non-emissions related fault.
The ECM supplies 5-volt power to sensors, switches, and actu-
ators external to the ECM. By supplying the power to these
devices, the ECM can accurately measure their output 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 condition 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 thresh-
old. This may be due to a wire harness short, device malfunc-
tion, or ECM power output circuitry failure.
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 discon-
necting device, observe system fault and determine if fault
has cleared. If fault clears, troubleshoot 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