Warning
Lights and the EGR Valve
by Austin Davis of TrustMyMechanic.com
Reader
Question: I
recently had the "service engine soon" light
come on my '94 Buick Century. Took it to my mechanic,
and he said it was the EGR valve which he changed out
for over $500. The light came on again within 24 hours
and I took it back. He said he tightened the fittings,
and said that the EGR computer may need to be replaced!???
Since then the "service engine light" has
gone off and come back on several times. What is going
on?
Dear
concerned car owner,
I
think you should ask for your money back. The onboard
computer system in your 1994 Buick Century is fairly
rudimentary compared to newer models and does not give
the most in depth diagnostic information. The EGR valve
is fairly expensive for your Buick, and the price sounds
ok. However, if the problem is still not resolved you
should ask to have your old valve re-installed
(you did ask to keep your old parts and their original
boxes didn’t you---?)
Tightening
the fittings is a cop out, and is probably his way of
saying “I don’t know how to fix it”.
The SES (Service Engine Soon) light can be very tricky
to turn off sometimes…..it is best to diagnose
the problem when the light is on. Every time you turn
off the car and re-start the engine, the onboard computer
does a sequential self check of all the sensors and
components on the car. If the car has not been driven
far or long enough, the system will not be able to complete
its test. This explains why the Check Engine Light won't
always come on. So as you drive, the light might come
on and stay on as the computer finds a fault during
its routine check list. Also the faulty component might
only malfunction at a certain speed or temperature which
is VERY common.
My
guess is that the EGR valve is NOT the problem, but
your mechanic received an EGR trouble code from your
computer system while running a diagnostic test. There
are more components of the EGR (Exhaust gas Re-circulation)
than the valve and any of those can cause an EGR trouble
code. If you can’t get your money back, have him
try his second diagnosis - a new computer (There is
no such thing as an "EGR computer" on this
car)at HIS expense to see if the problem goes away.
If you are a fairly regular customer at this shop, he
will want to fix this problem for you and keep you happy.
The price of an after-market computer should cost him
about $100, and the installation is simple and quick.
He will not be out as much money as you invested in
his mis-diagnosis.
My
gut says that this mechanic is not very computer savvy
and this is probably over his head. The computer is
usually the last thing to be replaced. Think of your
home computer…it is usually a software problem
that causes a glitch and not a problem with the hard
drive or mother board.
This
is what would have happened at my shop. This is how
your mechanic should approach tracing and repairing
an intermittent electrical problem:
