Dtc 642- 5 volt external low voltage, Dtc 642- 5 volt external low voltage -193, Diagnostic aids – JLG 450A_AJ Series II Service Manual User Manual
Page 243
SECTION 3 - CHASSIS & TURNTABLE
3121180
– JLG Lift –
3-193
DTC 642- 5 Volt External Low Voltage
• Engine Control Module.
• Check Condition- Key on.
• Fault Condition- ECM 5-volt output is below the accept-
able 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
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 actuator, smart sensors, smart actuators, etc.
After disconnecting device, observe system fault and
determine if fault has cleared. If fault clears, trouble-
shoot disconnected device for failures.
• With all 5-volt powered devices disconnected, look for
a change in fault state and measure ECM 5-volt output,
and verify it is within acceptable limits.
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2
1
6
1
3
1
2
1
5
V
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s
=
+
5
V
DC
5
V
_
rtn
T
P
S
1
T
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S
ER
+
+
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D
B
W-
D
B
W+
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C
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H
-B
rid
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1
9
T
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-
S
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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