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Just replaced catalytic converter, need advice re: O2 sensors

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Old 26 Jan 2017, 01:14 pm
Fresh Cruiser
Join Date: Mar 2015
Location: Windy Northern Arizona
Posts: 7
Default Just replaced catalytic converter, need advice re: O2 sensors

Hi! I have a 2009 base model PT Cruiser and I ran into some problems after a long trip out of state where the transmission was hesitating and shifting late, and downshifting at odd times, and gas mileage dropped by about 1/3rd. I took it to get a transmission flush and was told that with the issues they were seeing with the transmission they would not do a flush as they don't want to be responsible if it got worse. Fair enough, though when problems like I was experiencing develop, a flush was advised one of the first things to do to correct it, before taking other troubleshooting steps if that failed to correct it. BTW- the engine light had NOT come on and there were NO codes being reported!

So I took it to the local dealer and paid to have the transmission looked at. They found that the problem was a plugged catalytic converter and the transmission was fine (actually in real good shape was the way they put it). The issues I was seeing was a result of the lack of power from the engine due to the clog. They quoted me a price to replace the cat that was, well, astronomical ($2000), though it included replacing the oxygen sensors as well as a tranny flush. About $1200 of that was the cat itself (I think they must build them with 'unobtainium' rather than platinum!).

I looked around and no one locally had a cat that fit a PT Cruiser (even a universal cat of the correct size) and ended up ordering one online for delivery a week later (a direct fit Davico), as well as replacement oxygen sensors (upstream is a Standard Motors and downstream is a Spectra Premium). The car was still running and could be driven while waiting for the parts to arrive, and I HAD to be at a trade show in Las Vegas that week (an one and half hour drive from Kingman), so I went.

I made it to Boulder City before the problem became so bad that I couldn't go any further, and pulled into an O'Reilly's Auto parking lot. I waited for the car to cool down some for a few hours and tried again (engine wasn't overheating, but I allowed the cat to cool down), got about 1/4 mile and realized that was it and barely managed to make it back to the auto shop across the street from O'Reilly's.

While I was waiting for the cat to cool down earlier I had checked with them on replacing the cat and with O'Reilly's if a direct fit one was available. O'Reilly's had one that could be delivered from Las Vegas that afternoon before the auto shop closed, so I ended up buying a Magnaflow direct fit cat from them and having it installed by this shop, and had them do a transmission flush while we were waiting on the cat. From what I understand the Magnaflow cat is a bit better than the Davico, though it was twice the price. The cost to install the cat and the tranny flush were actually cheaper than I had been quoted in Kingman, so that was nice!

The rest of the trip went well, and as diagnosed by the dealer, it was the cat that was the problem. When I got home there were my new Davico cat and both oxygen sensors waiting for me, though I no longer needed the cat.

In all of this, there was never an engine check light and the dealer found no problem codes reported at all, not even for the oxygen sensors. I kept the old cat so I could see what the problem was and discovered it wasn't an issue with a cat meltdown, it just clogged up!

My working theory is that two years or so ago one of the places I had do my oil change had not replaced the air filter properly after checking it (I use a K&N permanent air filter, and tell them not to bother but they do it anyways) and my engine sucked dirty air for almost 6 months in a rural area with lots of dust. My guess is this is what eventually led to the cat being clogged, with the rest of the accumulated gunk in the engine finally being kicked loose once I started using Marvel Mystery Oil (to handle a gas pumping problem detailed elsewhere on this forum), finishing the job.

So I need advice, given the circumstances I detailed above, should I replace the oxygen sensors given there were never any fault codes and no obvious signs of oxygen sensor failure (such as a cat meltdown) or that was noted when the cat was replaced? Is it possible that whatever clogged the cat could affect the sensors without there being a fault code? I bought replacements, though my brand choices were driven mainly by cost, should I use them or wait for a problem to occur with the originals?

I described things in detail so as to get the best advice possible, and appreciate any help, even for things I may not of thought of.


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Old 26 Jan 2017, 01:52 pm
VsandFords's Avatar
Senior Cruiser
Join Date: Apr 2014
Location: Gladewater, Texas
Posts: 1,908
Default Re: Just replaced catalytic converter, need advice re: O2 sensors

My thought is, since you had to do repairs on the road and didn't replace them and you don't have a code, don't replace them at this time. You can always do that later when/if you throw a code.

Side note, if you still have the converter, you might want to sell it for scrap. I understand they can bring a pretty penny!
Life is just a bowl of jello, full of fruits and nuts.

2001 LE, auto, billet grille, tall shifter, polished aluminum spare, K&N filter and Hedman hedder. Why a header? Because it makes me happy!

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Old 26 Jan 2017, 02:55 pm
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Join Date: Sep 2015
Location: Phoenix AZ
Posts: 275
Default Re: Just replaced catalytic converter, need advice re: O2 sensors

if it aint broke, don't touch it...
yes cat are pricey but punching out the screens with a small pipe = FREE!
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