Using Your Digital Multimeter
Summary
Page 1 of 2
Here’s a quick review of the key Using Your Digital Multimeter
topics covered in this lesson. If you’re not familiar with any of these
statements, review the lesson once again to improve your
understanding.
Most basic control settings on the DMM are performed using
the rotary dial on the face.
When the meter is turned on, it goes through a quick power-
up self-test procedure that briefly displays all of the symbols
available on the meter. This includes a segment test to
ensure that all segments in the liquid crystal display are
working.
In addition to the rotary dial, the meter console contains eight
separate buttons used to select special functions. Some are selected after the
meter is already turned on, and some can be selected by pressing and holding
different buttons when the meter is first turned on.
When you select Min/Max, the meter will start tracking and recording the Minimum
or Maximum values measured by the meter. Min/Max works well with any
measurement scale such as volts, ohms, etc. MIN/MAX mode is useful for locating
intermittent drop-outs in circuits. MIN/MAX disables the meter’s Automatic
Shutdown feature, so it doesn’t power down during an extended circuit monitoring
session that can last half an hour or longer.
Zeroing the probes is an important step when you need a very accurate resistance
reading. The Zero function can be used to test the
repeatability of a throttle position or TP sensor.
Many people use the DMM’s ohmmeter to test injectors to
test for shorts or opens. Sometimes, an injector is clearly
shorted or open. Those are easy, but there are many
instances where a resistance test alone won’t provide a
guaranteed pass-fail grade for the injector being tested.
© 2004 National Automotive Parts Association – All Rights Reserved
Using Your Digital Multimeter
Summary
Page 2 of 2
Whenever you connect your ohmmeter to a circuit, make sure the power in the
circuit is off. Higher voltage and current in working automotive circuits can cause
permanent damage to your ohmmeter.
The DMM has an audible alert that can be activated with the push of a button and
acts as a watchdog during wiggle tests to help you nail those intermittent problems
in less time.
Some manufacturers use a throttle position sensor that contains both a position
sensor and a mechanical closed-throttle switch. You can use the ohmmeter and
Alert function to test these.
When you use the DMM as an ammeter, you connect one of the test leads to the
COM port and the other to the Amp or milliamp port. The test leads are then
connected in series with the circuit being tested, instead of being connected in
parallel to the circuit as they are during voltage test procedures.
To protect the DMM from an over-current condition, each of the ammeter circuits is
protected by a fuse which is very easy to blow.
The DMM really shines when it comes to testing working circuits for voltage drops
that can affect component performance. Voltage drops in a circuit reduce available
voltage at the load.
When testing a charging system, load the battery with your volt-amp tester, or turn
on as many vehicle accessories as possible. Then run the engine at the speed
recommended by the vehicle manufacturer where alternator output is highest.
To simulate the sweep of the analog meter needle, the DMM has a small moving
segment at the bottom of the display that sweeps back and forth as the digital
reading increases or decreases. The measurement range can be selected
manually with the meter Range button, or set to Auto-range by pressing and
holding the Range button until the display changes from Range to Auto.
© 2004 National Automotive Parts Association – All Rights Reserved
