Failing O2 sensor

[Polestar]

My C280 has 4 Oxygen sensors and the left after cat. has been failing for about 3 months. ( It trigers the ECL but then the ECl goes off for several weeks at a time)

1.) Is it true that when one O2 sensor needs to be replaced, you must replace all 4?

2.) Is it true that when one sensor goes out, the ECU will make adjustments (enfiching the fuel mix) untill it's replaced: so that no harm is done?

3.) After replaceing the sensor ( or all 4)
do you need to reset the long term fuel trim?

[Denlasoul]

I cannot specifically answer your questions, but it may be wise to replace all the O2 sensors at the same time. If you figure they are all about the same age, then it could be possible that one of the others is on the way out.

[stox]

I agree with Denlasoul, chances are that the remaining three O2 sensors are on their last legs, too.

[Ashkan's C280]

is your car a 2000?

[Polestar]

Mine is a 1999 model year.

See, I've asked my dealer and my mechanic and neither says it's necessary, however, some people choose to switch them all. My mech, who is an old time MB mech and very knowledgeabe., says, no damage will be done to the new one if the others are not replaced. Further, there is no labor advantage in switching them all, and the other three may last another 20K-30K mi.
(I read on some forum the O2 that's gone bad it notorious for failing)
You might be wondering why I'm asking if I already have info from people who should know? I guess it's because I want to take excellent care for my car, but don't want to throw money at something that I don't need to-who does. So, if someone said , you must do it or your engine will suffer, I'd replace all four.

BTW, thanks for the feedback guys, I really appreciate it.

[sig425]

1. Not really. Although it is true parts wear out at the same rate, one is assuming that each sensor gets the same amount of abuse. 2 sensors are before the cats and two after. It stands to reason that the ones after would get less abuse. The idea really comes from shops desires to charge more and from the idea that while its up there I might as well do them all. Only replace the one that is bad and you might find that the others last a long long time. FWIW, use a scan tool to reset the sensor a few times. Our heated sensors are prone to throwing codes when they are not bad. I reset mine 3 times and even bought the new sensor... the sensor is still in the box and the code hasnt shown up for 3 months.

2. It depends on which one goes out and how it goes out. If a sensor goes bad before the cat, the ecu might dump more fuel which will ruin a very expensive cat. After the cat is less of an issue than before.

3. When you replace the sensor you should use a scan tool to reset your ecu as it will still have the data from the bad sensor stored in it. The data is what controls the fuel trim I believe.. clean out the data and th etrim should change.


that's basically what i gathered when I went through this

[tpliquid]

and end up having lots of backfireing hehhe.

[sig425]

BTW, my sensor was failing due to the heat up cycle not due to any readings related to operation. So even with a faulty sensor, it was still doing its job.

I got most of my help here:
http://www.mercedesshop.com/shopforum/index.php3?

and from this guy:
http://catalog.mercedesshop.com/

he has really fantastic prices for factory parts. I got 2 OEM motor mounts for less than the price of 1 from the dealer.

[Polestar]

Thanks, sig425. :)

I actually have that link bookmarked, but haven't spent much time there.

Just curious, how did you find out the exact problem with your sensor? Was that in the DTC?
This sensor throws 2 codes. PO156 and PO161. The DTC for PO161 says, "heater circuit malfunction". It that the 'heat up cycle'

[Sulaco]

You can get alot of parts cheaper at www.importeccatalog.com
O2 sensors on the average are about $10 each cheaper.

With updated 202's like your's I'd say most of their parts are cheaper. For those of us with pre-update cars, it's more or less always cheaper.

[sig425]

I was getting 150 & 153 which are heater voltage errors. Reset it a few times and see what it does.

I was told that any heated 02 sensor can throw a lot of codes... even new ones.