JLG 600SC_660SJC Service Manual - Manual (Page 204)

SECTION 6 - TURNTABLE
6-58 – JLG Lift – 3121157
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
the 5-volt power output of the ECM below 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 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 calibration.
• 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 determine 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 out-
put of the ECM and verify it is within acceptable limits.
PINK/WHITE 4
3
5
1
2
TAN/ORANGE
GREEN/RED
PURPLE/BLUE
BLACK/GREEN