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Oxygen Sensor

The “check engine soon” light appeared yesterday on this nice running 1997 van with 167K. An auto parts store code check indicated a problem with the oxygen sensor. Is this something I can replace myself–a lightweight shade tree mechanic? I never seem to have any luck asking questions on the Mopar website. You guys are super.

Thanks, Dan

There are no codes that can tell you that you have a bad oxygen sensor.

What, exactly, was the code (looks like “P1234”)? If you don’t know just have it scanned again and write it down.

If it does come to replacing it, they’re sometimes shadetree work. But they screw into the exhaust pipe & are often difficult to access. So thing old, rusty, seized from heat and not easy to work on. You can always give it a whirl & then take it in if you give up. There are special sockets for these that you can “borrow” from many big chain-type auto parts stores.

Sure you can. All you need is an O2 sensor socket like this.


If it comes down to replacing the oxygen sensor, which may or may not be the cause of your code, these are generally considered shadetree mechanic work, although a little creativity and brute force can come into play. The last one I changed out was on my brother’s Jeep Cherokee, and it was kind of a pain to remove due to having seized into place over the 13 years it had been in place. Here’s where the creativity and brute force come into play. I couldn’t get enough leverage with my oxygen sensor socket or wrench (due to tool spreading and the threat of rounding off the hex on the sensor), so I broke the old sensor off flush, deliberately, of course, and used a standard 7/8" socket and long breaker bar to get it loose. Patience after this, to work it back and forth and slowly remove the sensor resulted in no damage to the threads in the bung and an easy installation, but this predicament would have sent many people to a repair shop. It’s good to know these kinds of things.

Do not rely on the oxygen sensor codes if the vehicle was scanned at an Autozone or something of the like. How does the vehicle run? Is it misfiring? Can you hear rushing air from the engine compartment? What were the other P codes if any? The oxygen sensors job is to update the ECM on how the engine is running. If there is a vacuum leak, a system too lean or rich condition, Autozone/Advanced Auto scan tools say the most likely thing wrong is the oxygen sensor when it is indeed reading correctly and reporting an abnormal condition.

I believe I have an o2 sensor problem but there is no code. My problem is the van runs great, there is an occasional hicup at around 40 mph though but the fuel economy has dropped. It has a 3.8 and I used to get 18+/23+ but that has dropped to 16/20. This started after the van sat once for about 5 months. With not having any noticable performance issues or codes I haven;t been able to pin point the problem. Can you help.

A bad O2 sensor should set a code especially in any vehicle that’s OBD II ('96-up). There’s a chance your MAF sensor needs cleaning or you have a vacuum leak.

I don’t actually put that much faith in the computer’s error reporting system. If there is a problem, the PCM will get around to reporting on it…eventually. So I’d not assume that no code yet doesn’t mean no O2 sensor problem.

However, given that all you have described is a hiccup at around 40 & a drop in MPGs you might as well get about 100 slips of paper & start writing stuff on each - O2 sensor, thermostat, spark plugs, air filter, fuel filter, dirty MAF, TCC clutch…

Then put the 100 pieces of paper in a hat and pull one out. Maybe you’ll get O2 sensor again.

What you really want to do is start your own thread, include complete vehicle info (including year, make, model, mileage, maintenance, etc…)

~ edit ~ I see that you have now done that:

Dan. every time I have had an oxogen sensor code it has been an oxygen sensor. You don’t need an oxygen sensor socket unless you are going to put the old one back in. Just cut the wire off and use a regular deep socket. If you don’t have deep sockets ,smash the porcelain off with a hammer. They go back in easily, you can use s box or open end wrench.

Well, I changed out the O2 sensor on my GF’s car and it took me about an hour. Autozone did a free diagnosis and told me it was the “downstream oxygen sensor” (there must be more than one). It’s been three years now since we got a new one and I don’t remember the codes, but, the Autozone guy, Argo, did the diagnostic for free and the code he got told him it was an O2 sensor. Then he looked on the Autozone computer and showed me a schematic that showed right where it was located under her car. I bought it for $80., installed it with a tool borrowed for free from Autozone and the car’s symptoms went away and haven’t returned for three years. The code indicated the oxygen sensor to Argo and he was right - or else he made a really great guess. BTW, she brought the car to the dealer before she told me about it and the dealer wanted to change out the “body module” for $2000. But, I’m glad we took it to Autozone and saved my GF $1920.

Great job, Frisbee!