The oxygen sensor code indicates that the oxygen sensor is returning a value that's out of acceptable range. That doesn't necessarily mean that it's bad. It may be working perfectly and doing what it's supposed to do. Compare the oxygen sensor in your car to a smoke detector in your house. When it goes off, you don't want to immediately assume that the smoke detector is bad -- you first need to figure out whether the smoke detector may in fact be right and you have a fire. Same with the oxygen sensor, except what it's indicating is not a fire but a problem with the fuel/air mixture the engine is getting.

Since you've had two oxygen sensors do the same thing, I think you can at least preliminarily conclude that the oxygen sensor itself isn't the problem. You may want to look for a misfire (possibly bad plug or wire), make sure the air cleaner is clean. If you can't find any obvious cause for the mixture to be off, you may want to take the vehicle to a good mechanic with diagnostic capabilities.

What gives is pulling a code and slamming a part is not the correct way to diagnose and attempt to repair a car. Attempting to do it that way wastes time and money, and then of course the misery is shared when you return a part under a "warranty" that has not truly been proven to be defective. In this field we see that as clear evidence of someone under the hood, "that does not know what they are doing".

Thanks for responses. Cowboyind,the engine does not misfire so we don't suspect a bad plug or wire. The gas mixture appears to be too rich for some reason, and apparently is causing check engine light to be on. John, we have purchased "new" parts in the past which have proven to be faulty, so it wasn't a waste of our time to try that possibility. My husband has a few cars to maintain for the family and has done so fairly successfully for over 20 yrs(including rebuilding transmissions), so I don't appreciate your comment much, especially since it had no constructive ideas to offer. So does anyone else have ideas--short of bringing the vehicle to a mechanic? We are trying to save some money and don't mind if we have to use some of our own time to accomplish this.

Could it be that with 190K miles on the clock that the injectors are worn and not spraying well.The fuel economy and power will reflect this..

Remove the plugs - are they carboned up ??

How is the engine compression ??

John is correct in that the sensor should have been checked before being condemned...But at one time these were a service item, good for , as an example, 60K miles..
The Cowboy has a excellent and informative way of stating things..

OK so you don't appreciate what I wrote, and sure I understand the fact that you dont. That does not make what I am saying wrong. The ability to do some work with cars, even transmission repair, and truly doing things correctly are two different things. If your husband got a job in a shop, and did that with someone elses car, what would that customer say?????

I've written hundreds of times here that pulling a code, and slamming a part is NOT the correct method to use, and that applies to anyone, not just real techs in real shops.

You said he has "the manual". Did he actually follow the trouble tree in the manual? What code is being set?

I agree with John G 200%. Ive had a customer pull his own codes and they hadn't a clue what they were doing but they
said " i know what i'm doing " . The code said bad O2,p.f.e
slow to respond e.g.r. and Map sensor. Well that car had a
rear A.B.S. brake system and the owner read the wrong codes and tested the wrong connector. After the brakes were
repaired, not related, the codes went away. Mind you if you buy after market JUNK you could get problems. Actually
you have those problems now. Reason being i've gotten a
notice that 2 things should NEVER be bought from after market dealers and that is 02 sensors and thermostats and
i agree. I've had nothing but trouble with after market O2 sensors and after market stats. I've been in this buisness 40 years and the dealers will use after market parts if requested but will refuse warranty if after market O2 sensors and stats are used. You get what you pay for. Rebuilding transmissions is mechanical, my 15 year old
nephew does that. No offence but code reading is easy but
figueing out what " triggered " the code is not that easy.
I'm sure you don't like my comment but you are not doing
yourself any favores. Send it out and spend the money. At
least if " they " screw up you have warranty. Just a thought of mine. Why are you posting this and not your
husband ? This is third hand info. for us.

I've never had a problem using an aftermarket O2 sensor, but that's been on Ford vehicles (Escort, Mustang, Contour, Contour). In fact, a couple of times I've ordered an SMP aftermarket sensor and it was the same exact make (NTK) that came on the Ford vehicle. Other than that I've used Bosch sensors which also work fine on Ford vehicles.

Anecdotally, I've heard that Bosch sensors do not work well on Chrysler vehicles. It wouldn't surprise me at all if other brands were fussy about O2 sensors, but far as I can tell, Ford vehicles are not.

I don't want to offend the professional mechanics, but I don't think, nor did I mean to imply from what I said above, that replacing the oxygen sensor as a "maybe" thing was necessarily a bad first step. On a 190k vehicle, it's not too much of a stretch to look at the code and figure that the oxygen sensor might be bad.

I've definitely had plenty of experience with taking vehicles to dealers and other places and having them throw parts at them until they finally stumbled onto what was really causing the problem, so I know that the trial and error approach is time-honored not just among do-it-yourselfers. A couple years ago I was out of town and was having a driveability problem with my Blazer; took it to a local shop and finally wound up with a $600 bill for replacing everything but the power window switches in an attempt to figure out why it wasn't running worth a crap. I don't know what part eventually did the job, but I am quite sure that it didn't need everything they stuck on it. Oh well, that other stuff probably would have gone bad sooner or later anyhow.

This in no way implies that all mechanics operate this way; I know the good ones don't. But if a part is cheap and a DIY person wants to try replacing it on the chance that it may be the problem, why not?

BrianI703. Funny how things work out. I'm specifically
talking about Ford with Bosch replacement parts ( O2 sensors and fuel pumps ). Replaced 7 O2 Bosch sensors in
a 98 Ford van. Got Pissed off and spent the money for the Ford part. No more codes. (customer money ). Made them
spend the money or get it out of my garage and don't come
back. They are happy now. No more codes. Go figure.

Once the 'check engine' light had been activated by a failed oxygen sensor, I believe, that for the Jeep, this code must be cleared after the sensor has been replaced, else it will continue to light the lamp. After-market code readers may not be capable of clearing this code. It may require a professional shop reader. This code is stored in non-volatile memory so disconencting the battery will not clear it.

Replacing the sensor will not clear this code.

The persistent nature of this code is, by design, to prevent the casual operator from clearing the code when the ozygen sensor needs replacing. This code is also set at scheduled maintence miles. Dealers will not clear this code (for their own protection) unless they, themselves, have replaced the oxygen sensor.

FWIW, I avoid aftermarket O2 sensors as much as possible. There is a clear difference in the O.E. part when it comes to accuracy and long term performance. That being said, when I see a part replaced and a code reset, my routine is to test the vehicle again from the beginning as if it has never been serviced the first time. This allows me to not assume that the part is either OK, nor defective. In otherwords, I test as if it's a completely different vehicle, and that routine allows me to solve problems that other techs/shops get stuck on.

Cowboy is correct that even a lot of techs get stuck in the pull a code, change a part trap. The funny thing is, they get that way because it's what the public wants. While I have a diagnostic fee to just get started, they may attempt to give into public price pressure and try and do the diagnostics for a vary small fee, or even FREE. Well this is just like anything else, you get what you pay for, sometimes even less. Overall the worst thing that happens is after the owner spends a ton of money whether by their own hand, or with someone elses help and they have been unsuccessful with a repair, then they show up at a shop like mine crying how they already spent all that money and the car is still broke, almost as if it's my fault and now I'm supposed to make it right without earning a living doing so. Quite frankly when it happens too many times I am not afraid to send the customer permanently out the door. The most recent was a person that owns an Infinity Q45. They fooled around several times over the last few years, and each time I bailed them out. This last time they came to me first, I did the diagnostics only to see them take the repair to another shop for $5.00 less than I was going to charge! Heck they spent that $5.00 in gas just getting to that other shop and back home. Well they are free to make that choice, and now they can live with it, because between me, and the dealer, no-one else has full software support for their car, and it will never come back in here. My Choice......

The vehicle is still not fixed, as far as I know - after all this postulating and arguing......
So, how about getting back to us, shel4 ??

And I fully agree with John, diagnoses and testing must be done, and NOT for free - this is not right - who in their right mind does things for "free" ???

On the Mustang I was getting codes during the engine-running self-test indicating rear/front oxygen sensor reading lean. A little troubleshooting revealed that the problem was caused by the thermactor air diverter (TAD) solenoid leaking, causing it to always divert the air pump upstream, causing a false lean indication.

I ordered new thermactor air solenoids (replaced both since the TAD solenoid had crapped out so the TAB was probably going to soon anyway, and they weren't very expensive).

In the meantime, the new injectors came (some of the injectors were leaking externally and I decided to replace them all) and I installed those.

I reran the self-test and instead of getting lean codes I got codes saying that the thermactor air is always upstream. It seems like there was something with the old injectors that wasn't allowing it to determine the cause of the lean condition.

A couple days later the solenoids showed up, I replaced them, re-ran the self test and it passed.

The suggested test for the Mustang, to determine if it's really a problem with the oxygen sensor, is to run the self-test with the engine coolant temperature sensor unplugged. If it then starts giving rich codes, the O2 sensor is working fine.

Thanks for your comments. Problem solved. Check engine light no longer on. Turned out to be a loose connection to car's computer. After my husband secured the connection , the problem was solved.

My 1995 Jeep grand cherokee is stating 600 RPM for about a 1 min half and then it goes back 300 RPM for about 1 min and then is goes back up 600 RPM it idling RPM