The secret of effective Automotive diagnosis and troubleshooting is to have a logical plan
The secret of effective automotive diagnosis and troubleshooting is to
have a logical, well-ordered plan. Following a logical step-by-step
procedure (flow chart) will get you to the root cause of a problem
quickly and efficiently. Repair manuals will have a diagnostic flow
chart that goes in a logical order. It will ask a question, usually yes
or no, and depending on the answer will branch off in two or more
directions. The last box in the flow chart will have the problem and how
to repair it. The example shown is a simple one. A more complicated
system will have branches going into specific tests and then have two or
more branches from there, depending on test results.
You will need some basic automotive diagnostic test equipment to
perform your diagnostics. A 12-volt tester (test light) will tell you if
a circuit has power or, when hooked up to the negative side of the
circuit, it will tell you if a ground circuit is good.
A good volt/ohm meter (VOM) will be needed to perform specific voltage
and resistance diagnostic tests. A digital meter is an excellent choice
because they are easier to read than an analog meter. I have both
digital and analog meters in my toolbox because sometimes an analog
meter is best for certain jobs. Most VOM's have an ammeter that will
test the alternator output and test for current draws. Make sure the one
you buy has one.
If you have an older car with a point equipped ignition system, you
will need a dwell meter to measure and adjust the dwell angle of the
points. A timing light will be needed to set and adjust ignition timing.
As with any piece of equipment, read the instructions that come with
your meter. It will tell you what the various functions are and how to
connect the meter to the circuit for accurate test results. Most meters
have a fuse in them to protect them from an incorrect connection. Make
sure the one you buy has a fuse and get a couple of spares. You will, at
some point, hook it up wrong and be very thankful you have the spares.
Most of the troubleshooting on today's cars will be electrical in
nature. A good wiring diagram is essential to properly troubleshoot and
diagnose any electrical circuit. They usually come in two parts; a
schematic and a wiring diagram. The schematic shows the different
components of a system and how they relate to each other. The wiring
diagram shows the actual wire colors and connections. On all vehicles
from 1995 and newer are OBDII vehicles and a scan tool will be needed to
retrieve fault codes and give you a starting point for your diagnostics
For testing the mechanical side of the engine, you will need some more
specialized equipment. A vacuum gauge with several adapters can be used
to test manifold vacuum and test vacuum operated circuits. A timing
light will help with checking ignition-timing and it can be a safe way
to test for ignition spark. A compression tester will show you the
condition of the piston rings, intake and exhaust valves.
Author: Regular Articles
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