JLG 1250AJP Service Manual - Manual (Page 215)

SECTION 3 - 1CHASSIS & TURNTABLE
3121171 – JLG Lift – 3-167
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 diag-
nostic 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 actu-
ators, etc. After disconnecting device, observe the sys-
tem 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