Dtc 642- 5 volt external low voltage, Dtc 642- 5 volt external low voltage -148, Diagnostic aids – JLG 450A_AJ Series II Service Manual User Manual
Page 188
SECTION 3 - CHASSIS & TURNTABLE
3-148
– JLG Lift –
3121290
DTC 642- 5 Volt External Low Voltage
• Engine Control Module.
• Check Condition- Key on.
• Fault Condition- ECM 5-volt output is below 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
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 ECM
5-volt power output below an acceptable threshold. This may
be due to a short in wire harness, malfunctioning device, or
ECM power output circuitry failure.
Diagnostic Aids
• Measure ECM 5-volt output while cycling key on with
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 throttle actu-
ator, smart sensors, smart actuators, etc. After disconnect-
ing 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 and measure ECM 5-volt output. 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