Dtc 642- 5 Volt External Low Voltage - JLG 1200SJP Service Maintenance Manual

SECTION 3 - CHASSIS & TURNTABLE

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 the
5-volt power output of the ECM below an acceptable thresh-
old. This may be due to a short in the wire harness, malfunc-
tioning device, or failure of the ECM power output circuitry.
3-166
4
P IN K /W H IT E
3
T A N /O R A N G E
5 G R E E N /R E D
P U R P LE /B LU E
1
2
B LA C K /G R E E N
Diagnostic Aids
– JLG Lift –
• 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 diagnostic cali-
bration.
• 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 actuators, etc. After
disconnecting device, observe the system fault and deter-
mine 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.
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