Troubleshooting with a Digital Multimeter
Special Tools
EL-39200 Digital Multimeter (DMM)
For equivalent regional tools, refer to
Special Tools .
Caution: Refer to
Test Probe Caution .
Digital Multimeter (DMM) Basic Requirements
Service information is validated using digital multimeters that
meet or exceed the following requirements. Using a multimeter that
does not meet these basic requirements may give inaccurate readings
which could lead to an incorrect diagnosis.
Display and Settings
2. |
Voltage, current, resistance,
frequency, diode test settings, and min-max function |
3. |
Display positive and negative
values |
Voltage
1. |
Have at least 10 MΩ
input impedance |
2. |
Test a DC voltage range of
0.1-1000 V. |
3. |
Test an AC voltage range of
0.1-1000 V. |
Current
1. |
Test a DC current range of 0.1
µA-10 A. |
2. |
Test an AC current range of
0.1 µA-10 A. |
Resistance
Test a resistance range of 0.1 Ω-40 MΩ and displays
infinite for a value greater than 40 MΩ (O.L. (Over-load))
Frequency
Test for a frequency range of 0.5 Hz-199 k Hz
Diode Test
1. |
Apply at least 1 mA when
performing the diode bias test |
2. |
Display the break over voltage
drop (0-3 V) of a forward biased diode |
3. |
Display infinite (O.L.
(Over-load)) when a diode is reverse biased |
Min-Max Readings
1. |
Can update at a 25 ms sample
rate |
2. |
Saves and displays minimum and
maximum values |
Note: Circuits which
include any solid state control modules, such as the engine control
module (ECM), should only be tested with a 10 MΩ or higher
impedance digital multimeter such as the EL-39200.
The DMM instruction manual is a good source of information and
should be read thoroughly upon receipt of the DMM as well as kept
on hand for future reference.
A DMM should be used instead of a test lamp in order to test for
voltage in high impedance circuits. While a test lamp shows whether
voltage is present if the impedance is low enough, a DMM indicates
how much voltage is present. In other words, if there is not enough
current, the test lamp will not illuminate even though voltage is
present.
The ohmmeter function on a DMM shows how much resistance exists
between 2 points along a circuit. Low resistance in a circuit means
good continuity.
Note: Disconnect the power
feed from the suspect circuit when measuring resistance with a DMM.
This prevents incorrect readings. DMMs apply such a small voltage
to measure resistance that the presence of voltages can upset a
resistance reading.
Diodes and solid state components in a circuit can cause a DMM
to display a false reading. To find out if a component is affecting
a measurement take a reading once, then reverse the leads and take
a second reading. If the readings differ the solid state component
is affecting the measurement.
Following are examples of the various methods of connecting the
DMM to the circuit to be tested:
• |
Probe both ends of the
connector and either hold the leads in place while manipulating the
connector or tape the leads to the harness for continuous
monitoring while you perform other operations or test driving.
Refer to
Probing Electrical Connectors . |
• |
Disconnect the harness at both
ends of the suspected circuit where it connects either to a
component or to other harnesses. |
• |
If the system that is being
diagnosed has a specified pinout or breakout box, it may be used in
order to simplify connecting the DMM to the circuit or for testing
multiple circuits quickly. |
|