Use the code reader as a starting point
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Photo 1: Plug in
Plug your code reader into the diagnostic
link connector under the dash
(engine off). Then start the vehicle and follow
the code reading procedure in the
Nothing can knock your day off track
faster than a “Check Engine” light
popping up on your dash. You wonder
if you should pull over and shut off
your vehicle or drive right to a shop. A
code reader/scanner can help you
make the drive/no drive decision
and even help you fix the
problem. It works by
plugging into the car's
computer system and
displaying a “trouble
A code reader/scanner is worth buying
if you're a fairly competent amateur
mechanic who understands how
an engine works. But it's not a silver
bullet that will always tell you exactly
what's wrong. It'll give you a head
start, but you'll still have to do some
detective work before you
start pulling and replacing
parts (more on this later).
The least expensive
units are simple
code readers that burp up an alphanumeric trouble code but
no information about what it means.
You'll have to look up the code in a reference
book or search the Internet.
Midpriced units actually
display the problem on the screen, like
“P0115 Engine Coolant Temperature
Circuit Malfunction.” One model even
accesses the Internet, so you can
upload the trouble code to a Web site
that has information on the most likely
cause of the problem.
But if you're a true grease monkey, go
for a more expensive scanner. A scanner
gives you real-time “live” information
so you see the same data your car's
computer is seeing. That saves you the
hassle of diving under the hood (with a
wiring diagram in hand), piercing
wires and taking sensor readings.
Code reading and scanning sound
simple, right? Well, there's more to it
than that. A code that indicates your
oxygen sensor is “lean” can mean the
sensor is dead, or it can mean that the
air/fuel mixture really is lean and
you've got either a vacuum leak or a
fuel problem. How do you know? Here
are three ways to get to the root of a
problem without replacing good parts.
- Go to the code reader/scan tool manufacturer's
Web site to see if it has
information on your trouble code.
- Take advantage of Internet forums.
Just search for your car's model and
add “forum” to the search term.
Register for the site (usually free) and
post your question, including your
vehicle's year, mileage, code number
and what you've done so far. You'll
be surprised by the number and
quality of responses you get.
- Subscribe to an online shop manual. It will have not only
all the carmaker's technical service
bulletins listed but also the complete
diagnostic procedure for your particular
code. It will walk you through
the testing procedure, telling you
which wires to check and what voltages
you should see. The services
also include component locators to
help you find the part in your vehicle,
and wiring diagrams showing
the connector position for each wire.