What's the deal on O2 sensors?

[pbm]

I've never replaced the oxygen sensors on my 2002 Buick Century which now has 108K. The car idles and runs perfectly. I thought my mpg's went down a little on the last tankful but it could be from using the AC.......so I go to Rockauto and I see that O2 sensors range from approx. 27 to 100 dollars each. I also see that there are 2 sensors, an upstream and a downstream (before and after the cat. conv.) When I checked E-bay there are several available (NTK, Bosch, no-name etc..) There are universal type and OE replacement type. Bosch lists several #'s that supposedly fit my vehicle (13444, 13474, 13193)
I'm confused. Can anybody explain whether it is necessary to change these and if so should I change both? Also which should I use? Any advice would be appreciated.

 

[StevieC]

You are going to get a mixed bag response on here regarding your question.

I'm of the opinion that if it isn't broke (No CEL on the dash) don't fix it! Sure the 02 sensor might not be 100% efficient, but you could get a new one that starts acting the same way after a shorter period of time so why not leave it in place until it's completely stopped working? Your car will still run if it's not functioning properly, just not at peak levels. So it's not like it will leave you stranded.

Besides, GM engine computers love telling people about problems and seem to really like turning on the CEL so I'm sure it will let you know!

When you do have to replace the 02 sensor(s) because the car won't pass emission tests, or has turned on the CEL, I would stick with an OEM brand. If your car came equipped with an NGK brand 02 sensor, this is what I would replace it with. (example)

I have never been a fan of universal 02 sensors as IMO they don't always fit your application 100%

I seriously hate pretty much anything BOSCH makes other than their oil filters because I feel it's just junk that creates nothing but headaches and this I have seen with my own eyes and it's not just speculation.

Your upstream O2 sensor (pre-cat) is the one your computer uses for fuel mixture settings, and the one downstream (post-cat) is just to ensure that your Catalytic converter is working. (looks for a change in exhaust gases pre/post converter by comparing both 02 sensor readings)

 

[xxch4osxx]

I have to agree with StevieC, stick with OEM O2 sensors if you are going to replace any of them. Heard many bad reports of the Bosch O2 sensors not working after a couple months.

 

[mechtech2]

I'd leave your present ones in for a while longer.
A change in how she runs, or a dash check engine light are the usual clues to replace them. They are tough to test properly.
With easy miles in a car in good condition, they can go much farther.

 

[JTK]

You've got more like 4 O2 sensors on your 2002 Century provided it's a 3.1L V6 in it. Just the 2 upstream sensors help determine fuel trim. Like the other Gents say, I'd leave them alone unless you've got a code pinpointing an issue.

 

[pbm]

Thanks guys. I'll leave well enough alone.

 

[StevieC]

Originally Posted By: pbm
Thanks guys. I'll leave well enough alone.
Like your Signature by the way!

Quote:


When the productive are 'required' to support the unproductive it only guarantees that more people will become unproductive

 

[Paul56]

I have a 2001 Neon with 181,000 kilometers (or 113,000 miles) and 2 O2 sensors. I don't know if those sensors have ever been replaced.

I have 2 brand new Mopar sensors sitting in my trunk that I have been procrastinating on getting installed... main reason is the vehicle works fine as it is now.

I'm beginning to think maybe I too will leave well enough alone... at least I have the parts if they go bad.

 

[Trav]

96 Toyota with recent Bosch O2 sensors throwing O2 codes.Replaced with Denso(OEM),end of problem.Contrary to what the advertisers would like us to believe cats and O2 sensors are not normal wear items like spark plugs and wiper blades.

 

[Colt45ws]

O2 sensors definitely are items that wear out.

 

[StevieC]

Originally Posted By: Onmo'Eegusee
O2 sensors definitely are items that wear out.
For sure, but let the computer tell you when it's due, don't replace based on mileage.

 

[Colt45ws]

Yes. I did replace the one on the Montana early when I did the LIM, but I have no idea how you would get to that with the engine together.

 

[StevieC]

Gotta love some of these manufactures. I think the designers have a bet at who can make things more complicated to get at.

 

[Buffman]

Originally Posted By: StevieC
Originally Posted By: Onmo'Eegusee
O2 sensors definitely are items that wear out.
For sure, but let the computer tell you when it's due, don't replace based on mileage.


02 sensors get lazy over years of use. They can report false conditions LONG before your car will set an CEL for them. I agree that replacing on mileage is not the best way to go, but unless you have a scanner to watch the 02s, it's a hard guess. Mainly the ones to be worried about are the pre-cat o2s. I always stick with OEMs on GM cars. Bosch units don't agree with GM..

 

[Trav]

"O2 sensors definitely are items that wear out."

For sure they do!So do pistons,valve guides,bearings and almost every other part of the car once it leaves the factory.In the 80s VW had a light that went off every 30K to change it as if it were a wiper blade,they stopped this practice after a short time after complaints about perfectly good sensors being tossed out.

True they can get slow as far as response time but time and mileage are not a good indicator of their condition,it seems to be more a case of the conditions they are subjected to during operation.Fuel quality,additives,gasket sealer's,blow by,fouling from excessive short trip operation,overheating etc all can play a part in their life span or response quality.

 

[StevieC]

I have a professional ODB-II scanner that hooks up to a PC ($5K) which my dad acquired for a discount, and I can watch the data stream in real time for all the sensors.

Very rare that I have seen a "lazy" sensor where the ECU didn't already have the CEL on. In some early models like pre-2000 I would agree, but since then the ECU's are pretty good at picking this up.

That said, I do a full checkup on my Santa Fe just before the winter. I check everything and change anything necessary to get me through Canadian winter when it is too cold to do big jobs. Nothing more than fluids/belts/plugs/wires yet but as the Santa Fe gets up there in age I'm sure it will need some sensors here/there and I would rather replace them in the fall than in February.

3/4 02 sensors have close to 200K KM (60K miles) and all appear to be working just fine when I do the live data test run with the graph. My computer also is very quick to go "closed loop" as well on start up.

When 1 of my upstream 02's went around 160K KM (100K miles) the ECU turned on the light and I did a live data run before replacing it and it was responding just fine with only a few blips in the graph on the live data test and not completely gone so this just verifies that computers today are very good at catching minute problems with 02 sensors in most cases!

Now my '95 Neon had a bad TPS which didn't turn on the CEL, but when you would snap the throttle it would hesitate and stutter a bit. When I put the live data monitor on it showed that the voltage wasn't changing.

 

[Trav]

I'm using the same kind of unit from Auto Enginuity.Nice unit,goes everywhere the laptop goes.My results mirror yours,
many cars with 100k+ and no issues.

The last car a saw with truly lazy O2 sensors was a 2005 Toyota Corolla with 60k.The engine was using oil and varnished badly,cams were also worn,burned about a ltr every 1k.

 

[The Critic]

Only the upstream ones need to be replaced.

Get a direct fit sensor, the universal ones are not worth the trouble.

I used a Bosch OE style sensor on my Saturn. It has been working flawlessly for the last 20,000 miles. I replaced mine because it triggered a CEL.

 

[StevieC]

I would add is that if the computer stores a Catalytic converter problem code, you might want to check the downstream 02 sensor before replacing the costly catalytic. It's rare that the downstream sensor is the problem but I have seen it enough not to warrant it being a fluke.

 

[tomcat27]

yes, if you get a an OBD scanner that will let you inspect the data stream, you can watch the sensors: the voltage should bounce all over the range from .1 - .99 If they stay towards the middle they are getting "lazy" and should be replaced.

ditto with the Bosch. I had one that was bad out of the box, and its replacement was bad within a week. after that I bought OE from the dealer and never had a problem. oh, and the dealer was cheaper than the bosch from AutoZone.