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Connect:
•
Black test probe to a good ground or the negative (-) vehicle battery post.
•
Red test probe to the wire that connects to the breaker points.
Press the "RANGE" button repeatedly to select the required number of cylinders.
Start the engine and observe the reading.
If the reading is too high or unstable, adjust trigger level by pressing the "±TRIG" button repeatedly.
7.
BASIC AUTOMOTIVE DIAGNOSTIC TESTING
A systematic series of tests that check the vehicle electrical system should be performed before testing
individual automotive components. The following basic tests check the primary areas responsible for the
majority of the electrical problems found in an automobile. Perform these tests first, even if a fault or trouble
code is set in the on-board computer. A basic ground problem in the electrical system can cause a component
malfunction detected by the on-board. If the problem is caused by a poor ground, simply replacing a failed
component will not provide a cure.
Basic diagnostic testing should begin by checking the main source of power and the chassis ground circuit
connections. Ground circuits are potentially the most troublesome areas of automotive electronics, yet they are
least understood and hardest to diagnose. One of the most frustrating electrical problems you will encounter
in an automobile is a high-resistance ground. This can create some very strange symptoms that seem to be
unrelated to the cause. The symptoms can include problems with turn signals, lights that stay dim, the wrong
lights turning on, transmission shifting problems, gauges that change when certain accessories are operated, or
even lights that will not turn on at all.
You can find a bad ground by checking the voltage drop between the component's ground wire and a clean
chassis ground or the negative vehicle battery terminal. An excessive voltage drop in a ground circuit affects the
entire electrical circuit. That is why it is so important to make sure the basic circuits are in good shape before
checking trouble codes in the on-board computer and individual components.
BATTERY TESTS
If you are having electrical problems, first test the battery. If the battery is low or discharged, it must be
thoroughly recharged before tests can begin.
A discharged battery may also indicate a problem in the charging circuit. Batteries are often blamed for "no-
start" conditions when, in fact, the real problem exists in the charging system. After a charging system problem
exists for some period of time, the battery becomes discharged and can not supply enough current for the
starter to crank the engine.
Many electrical problems are caused by current drains and shorts. Current drains that cause dead batteries are
often referred to as shorts, even though they are not actually short circuits. Shorts that blow fuses can be found
using the same troubleshooting techniques used to find current drains, even though the symptoms are different.
800.MACTOOLS
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