Are oxygen sensors a maintenance item, like spark plugs? - PeachParts Mercedes-Benz Forum

Honus · #1 02-29-2012, 02:14 PM

The service manual on my 1999 BMW 528i says to replace the oxygen sensors every 100,000 miles. Is that customary? I always thought you replace those when they went bad.

By the way, the BMW dealer quoted me about $330 per sensor. NAPA and Carquest sell them for about $65 a piece. They both sell Bosch, which is the same brand the dealer sells. My car has 4 sensors, so that is quite a difference.

MTI · #2 02-29-2012, 02:20 PM

You should get an OBDII "CEL" light when the sensor(s) need replacement. Yes, the price range is really incredible. Bosch sensors were used on a wide range of vehicles, so you're going to get the best deal from a parts shop than the dealer. For instance, on the W201/W124 cars, the Bosch O2 sensor was the same as used on later model Ford's V-8 Mustangs, and that FoMoCo part was a fraction of the MB part. Just had to adapt the wire harness.

tbomachines · #3 02-29-2012, 02:27 PM

They'll go bad after time but you'll know from decreased mileage, running rough, poor performance, etc. Should throw codes too AND the code will point to which one is bad. I would replace when they go, no need to spend the extra money.

Graplr · #4 02-29-2012, 03:59 PM

It is a maintenance item but I have yet to replace them on either of my 210s and both are over 100k. I will eventually replace them as preventative measures but I've got other things on the list first.

Sometimes the cheap ones from NAPA, etc require crimping your own wires. Not a big deal but some extra work for you (but results in pocket book savings).

compu_85 · #5 02-29-2012, 04:01 PM

I'd think by 99 the computer would be smart enough to tell when the O2S is bad.

-J

G-Benz · #6 02-29-2012, 04:10 PM

The O2 sensor does one thing...measure emissions.

Spark plugs gradually degrade to the point of adverse performance.

O2 sensors probably degrade to where they relay inaccurate information, so the adjustments performed by the engine management systems don't allow the engine to run optimally, or the emissions end up outside of allowable parameters...which in turn sets of the CEL.

Mistress · #7 02-29-2012, 04:13 PM

I (under the watchful eye and guidance of John Hef) replaced the 02 sensor in Maxine the Wonder Benz at 175,000. If it's not broken don't fix it.

Skippy · #8 02-29-2012, 04:59 PM

O2 sensors go bad gradually over time. When they do the inaccurate readings they generate tend to make the car run rich and get less good fuel economy. They have to be pretty bad before they will start setting codes though. If you're still getting good mileage and have no codes, I wouldn't worry about it. OTOH if you're mileage is suffering and the other usual suspects check out, it might be time to start thinking about your O2 sensors.

G-Benz · #9 03-01-2012, 09:59 AM

Replaced both on the Mustang after getting a code thrown by one...kinda figured it's best replacing in pairs anyway.

They run $50-60/apiece at AutoZone...made by Bosch. 15 minute DIY...

barry123400 · #10 03-01-2012, 07:53 PM

Well if you where able to measure and compare them to a new one. You would know if the time to change them was coming.

The computor should only throw a code once they exceed their design paremeters range excessivly. They could be close for a long time prior to doing that.

A pretty well total failure is basically what the computor is set up to indicate. A friend of mind changes his by milage to keep his fuel milage optimum. He does not seem to mind the cost. I. have to assume he keeps a pretty good track of his fuel milage, He told me it was benificial in his case.

PaulC · #11 03-01-2012, 08:27 PM

Would a bad O2 sensor allow the air/fuel mixture become rich enough to fry the catalytic convertors? That might be an argument to replace them before failure if that is true.

tbomachines · #12 03-01-2012, 08:46 PM

Quote:

Originally Posted by PaulC

Would a bad O2 sensor allow the air/fuel mixture become rich enough to fry the catalytic convertors? That might be an argument to replace them before failure if that is true.

Yes but again it would be throwing a code long before that happened. That also assumes the other O2 sensors fail simultaneously (most newer cars have several).

G-Benz · #13 03-02-2012, 11:16 AM

Depends.

My former W124 never threw a code, but had misfiring issues and wouldn't pass emissions at one time.

Turned out to be bad plug wires. Actually one wire was worn bad to the point that the plug attached to it fouled, and enough unburnt fuel went out the exhaust and foul the O2 sensor...all the while never throwing a code!

tbomachines · #14 03-02-2012, 11:20 AM

Quote:

Originally Posted by G-Benz

Depends.

My former W124 never threw a code, but had misfiring issues and wouldn't pass emissions at one time.

Turned out to be bad plug wires. Actually one wire was worn bad to the point that the plug attached to it fouled, and enough unburnt fuel went out the exhaust and foul the O2 sensor...all the while never throwing a code!

Was it an OBDII car? Earlier w124s were not OBDII, I don't think they had O2 sensors looped into the CEL. My O2 sensor went as well in my 300E without a CEL.

Honus · #15 03-02-2012, 11:28 AM

Quote:

Originally Posted by PaulC

Would a bad O2 sensor allow the air/fuel mixture become rich enough to fry the catalytic convertors? That might be an argument to replace them before failure if that is true.

I agree. I also wonder whether a bad O2 sensor could caused the mixture to be rich enough to affect the lubrication of the upper part of the cylinders.