MAINTENANCE OF M939 SERIES VEHICLES - OD1661 - LESSON 1/TASK 2
reading received is within these limitations, therefore SGT Metcalfe
will proceed with No-Go test 80.
No-Go Test 80.
While cranking an engine with bad or discharged
batteries, it is possible for the VTM to lose
power and come on again after the cranking has
stopped displaying four dashes (- - - -).
this occurs, clean the battery posts and clamps
and try again.
If the VTM still loses power,
another vehicle and perform the following tests,
using the test probe cable W2.
Step 1. In the first step, SGT Metcalfe installs the current probe
around the output wire of the alternator/generator.
Then he points
the arrow on the probe away from the alternator/generator.
this is done SGT Metcalfe performs the current probe offset.
SGT Metcalfe first turns off all vehicle electrical power.
Then he dials 74 into the TEST SELECT switches and presses and holds
the TEST button until the CAL message appears on the display. When
the word CAL appears, SGT Metcalfe releases the TEST button and waits
for the offset value to appear on the display.
The offset value
should be between -225 and +225. Since the offset value was between
these limits, SGT Metcalfe will proceed to step 3 and check the
Step 3. SGT Metcalfe first shuts off the fuel and then presses the
TEST button. When the word GO appears on the display, he cranks the
engine. SGT Metcalfe stops cranking the engine when either the word
OFF or an error message are displayed.
Since the word OFF was
displayed, SGT Metcalfe will proceed to step 4 and check the starter
Step 4. SGT Metcalfe dials 90 into the TEST SELECT switches and presses
the TEST button. Now he cranks the engine for a few seconds with the fuel