DDEC TROUBLESHOOTING
4.5
USE OF DIGITAL VOLT-OHM METER
Before using this manual, you should be familiar with the digital volt-ohm meter (VOM). You
should be able to measure voltage and resistance. You should be familiar with the controls of the
meter and how to use it correctly.
For use of a typical digital volt-ohm meter, refer to section 4.5.1, refer to section 4.5.2, and
refer to section 4.5.3.
4.5.1
Resistance Measurements
Perform the following steps to measure resistance:
1. Connect the red test lead to the V-
(Volt-Ohm) input connector and the black lead
to the com input connector on the meter.
2. Set the function/range switch to the desired
position. If the magnitude of the resistance
is not known, set the switch to the highest range, then reduce until a satisfactory reading is
obtained.
3. If the resistance being measured is connected to a circuit, turn off the power to the circuit
being tested. Turn off the ignition.
4. Connect the test leads to the circuit being measured. When measuring high resistance, be
careful not to contact adjacent points, even if they are insulated. Some insulators have a
relatively low insulation resistance which can affect the resulting measurement.
5. Read the resistance value on the digital display.
4.5.2
Continuity Checks
In addition to measuring the specific resistance value of a circuit, some meters will also register if
a continuous electrical path exists. If a path exists, the circuit is said to have continuity. (This
continuity check can be used in any section of this troubleshooting guide where the test is looking
for greater than, less than, or equal to 5 ohms.) An open circuit (broken electrical path) would have
resistance and would not have continuity. To utilize the continuity feature of certain meters:
1. Place the function/range switch in any
range.
2. Connect the red lead to the V-
connector and the black lead to the com connector on the
meter. With the test leads separated or measuring an out-of-range resistance, the digital
display will indicate OL (over limit) Some meters show "1 +, 1, or ."
3. Put one test probe at one end of the wire or circuit to be tested. Use the other test lead
to trace the circuit. When continuity is established, an ohm ( ) symbol will display
in the upper left corner of the digital display. If contact in the wire is maintained long
enough (about 1/4 second), the OL will disappear and the resistance value of the wire
or circuit will display next to the symbol.
4. If your VOM does not work in the manner described above, you must know how your
VOM operates in order to use this troubleshooting guide.
All information subject to change without notice.
6SE497 9709 Copyright © 1997 DETROIT DIESEL CORPORATION
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