If you are going to keep your car for awhile, go ahead and replace the O2
sensor(s) if you suspect it is bad. It is likely that it will eventually go
bad anyway. I had my front break pads replaced even though there was
probably another 10,000 miles on them, because my car was in the shop for
something else and my time was too valuable to worry about having to replace
the pads later.

Regarding the recommendation from Bosch, remember that on new cars the
tune-up interval is 100,000 miles (mainly because the only thing in a
tune-up these days is replacing the platinum spark plugs). Also remember
that they are in business to make money, and the more Bosch products you
buy, the more money they make.

<snipped>>

Keep in mind that on a 5 year old vehicle operated where salt is used on
roads, the O2 sensor may be rusted in place.  Hopefully, this won't be the
case, but be prepared to replace the exhaust manifold as well (probably an
extra $300 or so) if it strips when removing the old sensor.  In my 35 years
(some of it spent fixing cars that dealers couldn't fix) or so working on
cars, I have become a big believer in the adage, "if it ain't broke, don't
fix it."

You may get 1 or 2 MPG better fuel economy with a new sensor.  People claim
bigger improvements, but I doubt if your fuel economy will improve more than
that.  There is also the possibility that your sensor is fine and you will
see no measurable improvement in fuel economy.

You can do the math on whether or not replacing the O2 sensor might be cost
effective.

Here is an example:
10,000 miles driven per year divided by your current MPG (25 in this
example) = 400 gallons of fuel
400 gallons of fuel times an average fuel price of $.50 = $600 in fuel.

10,000 miles divided by (the improved 26 MPG) = 384.6 gallons of fuel
384.6 X $1.50 = $577 in fuel, or a $23 improvement over 10,000 miles.

10,000mi. divided by 27 MPG = 370 gallons
370 X $1.5 = $555 in fuel, or a $45 improvement.

Assuming that you do not need to spend additional money to replace the
exhaust manifold and that the cost of a replacement O2 sensor is $60 with no
labor and you already have the tools to do the job, a $23 improvement will
take a little under 3 years at 10,000 miles per year to break event, and a
$45 improvement will take about a year and a half to break even.

Obviously, there are a lot of variables in this equation.  More miles driven
and higher fuel costs will speed up the break even, and higher replacement
costs like a stripped manifold, including labor charges, or lost
productivity while the vehicle is not usable will slow down or even
eliminate any savings.

Unless something is actually malfunctioning, there usually is not one trick
or fix that will make a dramatic improvement in fuel economy.  There are a
lot of other things you can do that can add up to improved fuel economy, and
a lot of them cost nothing to implement or are part of routine maintenance
that is recommended by the folks who designed your car.

This is an apples and oranges comparison, but my car with a 4.3 liter V8
gets 18 city/26 hwy in the winter, 19/27 in the summer with the original O2
sensor.  The 4.3 liter is roughly 2.3 times the displacement of the 1.8
liter in a Corolla but I doubt if the Corolla gets 2.3 times the fuel
economy.  I', cheap so I only use the tricks that cost me nothing to improve
fuel economy.

Shoot. You know, kinda like the ad: Seeking woman with bass boat; Object:
Matrimony. Please send picture of boat...  ;)

First generation heated O2 sensor

I'd have more faith in a website that isn't trying to sell the very
product it's describing, like this one:

     http://tinyurl.com/6ldlld

     http://d-tips.com/General/Articles/article.aspx?id=/clients/Testing/Oxygen+Senso
r+Testing/o2_sensors.art

I've never heard of an oxygen sensor needing replacement as long it
could put out a hefty signal and its heating element worked (Ray?
Tegger?  Am I wrong?), so I wouldn't automatically replace it at any
fixed mileage interval.  Some cars provide ways to check the sensor
indirectly, such as through a terminal that puts out an amplified
version of its signal or by blinking the Check Engine light in a funny
way (my 1998 Nissan shows the duty cycle of the sensor that way).

n...@wt.net wrote:

..or stolen.  It finally happened to my Nissan Frontier, but at least
the thieves simply unbolted mine and didn't saw through the exhaust
pipes.

I put in a cat made by Eastern Catalytic.  Are they any good?   My
truck is OBD II but doesn't have an O2 sensor downstream from the cat,
and the emissions testing stations here don't stick a probe into the
tailpipe of OBDII vehicles.