http://www.mccd.edu/faculty/gregorya/AT%2043/AT%2043%20Lecture%20PowerPoints/AT%2043%20Ch%209%20Digital%20Meters.ppt by Aaron Gregory

2. TEST LIGHTS
• A test light is one of the
simplest testers that can be
used to detect electricity.
• A test light is simply a light
bulb with a probe and a
ground wire attached.
FIGURE 9-1 A 12-volt test light is attached
to a good ground while probing for power.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

3. TEST LIGHTS
FIGURE 9-2 A test light can be used to locate an open in a circuit. Note that
the test light is grounded at a different location than the circuit itself.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

4. TEST LIGHTS
Continuity Test Lights
• A continuity light is similar
to a test light but includes a
battery for self-power.
• A continuity light illuminates
whenever it is connected to
both ends of a wire that has
continuity or is not broken.
FIGURE 9-3 Self-powered test lights contain a
battery, clamp, and probe. This type of test light
should not be used on any computer-controlled
circuits because the applied voltage can
damage delicate electronic components or
circuits.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

5. TEST LIGHTS
LED Test Light
• An LED test light uses an
LED instead of a standard
automotive bulb for a visual
indication of voltage.
FIGURE 9-4 High-impedance test light. An LED test light can be easily made using
low-cost components and an old ink pen. With the 470 ohm resistor in series with the
LED, this tester only draws 0.025 ampere (25 milliamperes) from the circuit being
tested. This low current draw helps assure the technician that the circuit or
component being tested will not be damaged by excessive current flow.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

6. TEST LIGHTS
Logic Probe
• A logic probe is an
electronic device that lights
up a red (usually) LED if the
probe is touched to battery
voltage.
FIGURE 9-5 A logic probe connected to
the vehicle battery and relay used to check
for power, ground, or a pulse.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

7. DIGITAL MULTIMETERS
• Digital multimeter (DMM) and digital volt-
ohmmilliammeter (DVOM) are terms commonly
used for electronic high-impedance test meters.
• High-impedance meters, required for measuring
computer circuits, are digital meters; however, not
all digital meters have the required 10 megohms (M)
(10 million ohms) of internal resistance.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

8. DIGITAL MULTIMETERS
FIGURE 9-6 Typical digital
multimeter. The black meter
lead always is placed in the
COM terminal. Except when
measuring the current in
amperes, the red meter test
lead remains in the V
terminal.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

9. DIGITAL MULTIMETERS
FIGURE 9-7 Common abbreviations used on the display
face of many digital multimeters. (Courtesy of Fluke
Corporation)
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

10. DIGITAL MULTIMETERS
FIGURE 9-8 A summary chart indicating what measurement type may be
used to test which vehicle system.(Courtesy of Fluke Corporation)
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

11. DIGITAL MULTIMETERS
Measuring Voltage
• A voltmeter measures the pressure or potential of electricity
in units of volts.
FIGURE 9-9 A typical autoranging digital
multimeter automatically selects the proper
scale to read the voltage being tested. The scale
selected is usually displayed on the meter face.
(a) Note that the display indicates “4,” meaning
that this range can read up to 4 volts. (b) The
range is now set to the 40 volt scale, meaning
that the meter can read up to 40 volts on the
scale. Any reading above this level will cause
the meter to reset to a higher scale. If not set on
autoranging, the meter display would indicate
OL if a reading exceeds the limit of the scale
selected. (Courtesy of Fluke Corporation)
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

12. DIGITAL MULTIMETERS
Measuring Voltage
FIGURE 9-10 Typical digital
multimeter (DMM) set to read DC
volts.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

13. DIGITAL MULTIMETERS
Measuring Resistance
• An ohmmeter measures the resistance in ohms of a
component or circuit section when no current is flowing
through the circuit.
• An ohmmeter contains a battery (or other power source).
– When the leads are connected to a component, current flows through
the test leads and the difference in voltage (voltage drop) between
the leads is measured as resistance.
• Zero ohms on the scale means no resistance between the
test leads, indicating that there is continuity or a continuous
path for the current to flow in a closed circuit.
– Infinity means no connection, as in an open circuit.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

14. DIGITAL MULTIMETERS
Measuring Resistance
FIGURE 9-11 Using a digital multimeter set to read ohms () to test this
light bulb. The meter reads the resistance of the filament.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

15. DIGITAL MULTIMETERS
Measuring Resistance
FIGURE 9-12 Typical digital
multimeter showing OL (over
limit) on the readout with the
ohms () unit selected. This
usually means that the unit
being measured is open
(infinity resistance) and has no
continuity.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

16. DIGITAL MULTIMETERS
Measuring Resistance
FIGURE 9-13 Many digital multimeters
can have the display indicate zero to
compensate for test lead resistance.
(1) Connect leads in the VΩ and COM
meter terminals. (2) Select the Ω
scale. (3) Touch the two meter leads
together. (4) Push the “zero” or
“relative” button on the meter. (5) The
meter display will now indicate zero
ohms of resistance. (Courtesy of Fluke
Corporation)
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

17. DIGITAL MULTIMETERS
Measuring Amperes
FIGURE 9-14 In this digital multimeter set
to read DC amperes, note that the red lead
is placed in the far left-hand socket of the
meter. The meter is displaying the current
flow (4.18 A) through the electric fuel pump
on this General Motors 3800 V6 engine.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

18. DIGITAL MULTIMETERS
Measuring Amperes
• An ammeter measures the
flow of current through a
complete circuit in units of
amperes.
• The ammeter has to be
installed in the circuit (in
series) so that it can
measure all the current flow
in that circuit.
FIGURE 9-15 An inductive ammeter
clamp is used with all starting and
charging testers to measure the current
flow through the battery cables.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

19. AC/DC CLAMP-ON DIGITAL MULTIMETER
• An AC/DC clamp-on
digital multimeter (DMM)
is a useful meter for
automotive diagnostic work
and uses a Hall-effect
sensor to measure current.
FIGURE 9-16 A typical mini clamp-on-type digital multimeter.
This meter is capable of measuring alternating current (AC)
and direct current (DC) without requiring that the circuit be
disconnected to install the meter in series. The jaws are
simply placed over the wire and current flow through the
circuit is displayed.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

20. AC/DC CLAMP-ON DIGITAL MULTIMETER
FIGURE 9-17 An AC and DC
current clamp such as the one
shown can be used with a regular
digital multimeter. The amp probe
contains a separate battery and
electronic circuit that converts the
amperage reading into a millivolt
(mV) signal.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

21. FUSE YOUR METER LEADS!
FIGURE 9-18 Note the blade-type fuse holder soldered in series with one of the
meter leads. A 10 amp fuse helps protect the internal meter fuse (if equipped)
and the meter itself from damage that might result from excessive current flow if
accidentally used incorrectly.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

22. “OL” DOES NOT MEAN THE METER IS READING
“NOTHING”
FIGURE 9-19 A summary of the test meter hookup.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

23. ELECTRICAL UNIT PREFIXES
• Electrical units are
measured in numbers such
as 12-volts, 150 amperes,
and 470 ohms.
• Large units over 1,000 may
be expressed in kilo units.
• Kilo (k) means 1,000.
FIGURE 9-20 Always look at the meter display when a measurement is being
made,especially if using an autoranging meter.(Courtesy of Fluke
Corporation)
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

24. HOW TO READ DIGITAL METERS
• Getting to know and use a digital meter takes time
and practice.
• The first step is to read, understand, and follow all
safety and operational instructions that come with
the meter.
• Use of the meter usually involves the following
steps.
– Select the proper unit of electricity for what is being
measured.
– Place the meter leads into the proper input terminals.
– Measure the component being tested.
– Interpret the reading.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

25. METER USAGE ON HYBRID ELECTRIC VEHICLES
FIGURE 9-24 Be sure to only use a meter that is CAT III rated when taking
electrical voltage measurements on a hybrid vehicle.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458

26. METER USAGE ON HYBRID ELECTRIC VEHICLES
FIGURE 9-25 Always use meter leads that are CAT III rated on a meter that is
also CAT III rated to maintain the protection needed when working on hybrid
vehicles.
Automotive Fuel and Emissions Control Systems, 2/e © 2009 Pearson Higher Education, Inc.
By James D. Halderman and Jim Linder Pearson Prentice Hall - Upper Saddle River, NJ 07458