Change O2 sensor or Catalytic Converter?

[FirstNissan]

Hey guys, a coworker just failed inspection for a CEL. Hes got an older camry, says that Autozone told him it was either an O2 sensor or his Catalytic converter.
He asked me (I had no clue!) whether just changing the O2 sensors initially would be ok or not. He's worried that if the O2 sensors get changed, can a bad Cat cause them to fail? If he has to change the cat, its got to be done, but is there any harm in trying the sensors first?
Thanks for the help!

 

[FL_Rob]

Did A/Z put a scantool on it or is an opinion/guess/shot in the dark?

 

[FirstNissan]

He said that AZ put a scanner to it, pulled up a bat cat code, and sais that it was either the cat or the O2 sensor, unsure of which.
Hes worried that he will have to buy O2 sensors twice, if the first set go bad from a bad cat, is that possible?

 

[Burt]

Driving with a bad O2 sensor can ruin a catalyst, but a bad catalyst can not ruin an O2 sensor.

So both could be bad, but there ought to be a way to confirm whether the O2 sensor is working. You might want to go to another store. What was the code number from the reader?

 

[lexus114]

Originally Posted By: Burt
Driving with a bad O2 sensor can ruin a catalyst, but a bad catalyst can not ruin an O2 sensor.

So both could be bad, but there ought to be a way to confirm whether the O2 sensor is working. You might want to go to another store. What was the code number from the reader?



Yep, if you could get that for us, it would be a big help.

 

[JHZR2]

Yeah the code would be good. Ill bet it was the catalyst nt operating code, which could be the second O2 sensor. Cat efficiency is determined by comparing the O2 sensor characteristics pre and post catalyst. If the rear especially is faulty, then the reading may not be right and it could register the code.

"older" camry = >75k and still original O2 sensors? If so, Id start there. Worst thing that could happen is that the cat is still bad, in which case Id want to rebuild the whole system anyway, given age/mileage.

 

[FirstNissan]

Just got off the phone with him, code was P0420, older camry=2002 with 125K miles, original O2 sensors and cat.

 

[dlafoy]

Code P0420!!!!! Come on guys this dude is obviously smoking something

 

[IndyIan]

I'd change the O2 sensor first, as its easier and they seem to fail far more frequently than cats IME.
Also I guess he could simply use his nose to help diagnose a bad cat. If he drives around for 10 minutes and smells gas at the exhaust pipe, the cat isn't working well or is overwhelmed with fuel.

 

[FirstNissan]

Thanks for the input guys! Should I suggest he buy 2 new O2 sensors or just the rear one?

 

[Bladecutter]

Both.

You could also pop the converter off, and shake it to see if the catalyst is broken and loose inside before deciding to replace it, if the converter is easily removable on the Camry.

BC.

 

[Vikas]

If either you or your friend is serious, search for P0420. One could write a whole book on it just from the information which exists in this forum.

- Vikas

 

[MarkM66]

I recently had a cat go bad on my Civic. I could tell the cat was not flowing correctly because the engine couldn't pull to red line at WOT.

I also got code P0420 . Which doesn't pinpoint if it's the cat or the 02.

http://www.obd-codes.com/p0420

I'm in a non emissions testing area, so I just eliminated the cat and extended the 02 so the CEL doesn't come on. Via this method;

http://www.civicforums.com/forums/79-forced-induction-swaps/240602-diy-mechanical-o2-simulator.html

Works and runs fine now.

 

[AdRock]

Putting a new rear sensor is much cheaper than replacing the cat. Change it out, reset the ecu and see if the CEL comes back on after driving a while.

 

[ponderosaTX]

The ECU/ECM (engine computer control) compares the readings of the pre-cat and post-cat O2 sensors. A P0420 code indicates that the post-cat sensor (on Bank 1 which is the only bank on a 4 cylinder vehicle) has O2 readings similar to the pre-cat O2 sensor implying the cat is no longer working properly. Of course, many vehicles have two cats in series and the O2 sensors only monitor the first cat. The actual tailpipe emissions can be clean but the OBD-II monitoring system implemented by the ECU will still flag a weak first stage cat.

If your failing cat does not impede exhaust flow, you can install spark plug anti-fouler spacers on the post-cat O2 sensor to attenuate the O2 readings at that sensor and thereby convince the ECU that the failing cat is working properly. This trick is very well-documented on various forums on the web. See for example:

http://forum.mpvclub.com/viewtopic.php?t=22162

If you cat is clogged then your engine will not run properly unless you replace the cat.

 

[Sayjac]

Quote:
Code P0420!!!!! Come on guys this dude is obviously smoking something

LOL If one owns an 02-03 2.5L Altima, Sentra and perhaps some other Nissans, code 0420 most likely means it's too late. The precat has already dumped material into the engine, the cylinder walls have been badly scored and the engine seriously damaged. At least the worst the OP's friend likely may have to deal with is a couple of O2 sensors and/or a catalytic converter, not, as in Nissan's case, a new engine.

Never thought about the 0420 deal though, perhaps that's what the engineers, if one can call them that, at Nissan were doing/thinking about, when they designed Nissan's exhaust/precat system. 0420, yeah that's the ticket.

 

[Rix]

*SIGH*

GO TO A DEALER!!

At least have it (the vin) run to see if the ECU update for code p0420 is available.

TSB# EG024-04

OR PM me the vin, and I'll check and see if it's got anything in history. Might or might not be able to tell anything.

 

[Warstud]

Originally Posted By: Bladecutter
Both.

You could also pop the converter off, and shake it to see if the catalyst is broken and loose inside before deciding to replace it, if the converter is easily removable on the Camry.

BC.


No need to remove it...just pound on it with the back of your fist and listen for loose pieces rattling around.

 

[Rix]

The cats generally don't come apart inside on the camrys.
They just throw codes.
I've had one that plugged.