Replace O2 sensors with new catalytic converter?

[NissanMaxima]

Hi all,
I'm getting a catalytic converter efficiency below threshold error with my scanner on my Highlander. CEL is on. The dealer is pretty confident it needs a new catalytic converter but will still run diagnostics to confirm. I would think it would be prudent to replace both O2 sensors rather than transfer over 20 year old sensors but the dealer says they always just transfer over the old ones. Am I off base on this one? From what I've read, the old ones can be difficult to get out and may even be damaged. Car has about 130k miles by the way. Thanks for any input!

 

[JDenyer232]

I would replace them if it were my vehicle.

 

[researcher]

Dealer isn't wanting to replace them probably to get future business from you when they go bad. Over time O2 sensors get lazy, they don't throw a check engine light right away.. Yes replace them when you replace the catalytic.

 

[Furious]

You might want to consider trying some cataclean instead of spending a ton of money on a catalytic converter.

Anyways if you replace the cat replace the oxygen sensors, no if ands or buts about it especially at 130,000 miles.

 

[trd1zz]

20 year old exhaust? The sensors would probably be damaged anyways during removal.

 

[ka9mnx]

After about 115k miles, O2 sensors are on life support.

 

[Speedbird001]

20 year old exhaust? The sensors would probably be damaged anyways during removal.

Oh yeah, they have got to be fused as a single piece of matter by now, especially if you live anywhere that treats the roads in the winter. I would do cat back while I was at it...

AND, start hosing the forward pipe / connector / O2 sensor [socket] NOW. Will greatly increase the chances of successful R&R when the time comes.

 

[slacktide_bitog]

They are worth replacing with the cat.

You might want to consider trying some cataclean instead of spending a ton of money on a catalytic converter.

Anyways if you replace the cat replace the oxygen sensors, no if ands or buts about it especially at 130,000 miles.

also this

Cataclean is worth trying first.

 

[NissanMaxima]

Thanks! You folks are the best! And funny too. @Speedbird001 ... single piece of matter! Here in Colorado, not a ton of road salt used and underside looks great but it just makes sense to me to replace the sensors as part of the job especially after reading some of the arguments here for it. One thing I'm confused about is that the service advisor (who says he used to be a technician) told me there is one sensor to transfer over, but the parts people (whom I've known for 24 years now and trust) said there are two - one they called an air fuel sensor. Do both of them thread into the catalytic converter or a connector that is removed as part of the process? Or is one of them separate from this job? Also, would it make sense to have them replace the sensors on the other catalytic converter (bank 1)? I'm going to show my ignorance here now, but does putting in two new ones with the new cat cause any sort of "imbalance" with the other two on the other bank 1 cat?

AND, start hosing the forward pipe / connector / O2 sensor [socket] NOW. Will greatly increase the chances of successful R&R when the time comes.

Also, if I have them replace the sensor, not sure what you mean here about hosing down the sensor. But I should still crawl under the car and spray any connections with PB Blaster to help them out?

 

[researcher]

Thanks! You folks are the best! And funny too. @Speedbird001 ... single piece of matter! Here in Colorado, not a ton of road salt used and underside looks great but it just makes sense to me to replace the sensors as part of the job especially after reading some of the arguments here for it. One thing I'm confused about is that the service advisor (who says he used to be a technician) told me there is one sensor to transfer over, but the parts people (whom I've known for 24 years now and trust) said there are two - one they called an air fuel sensor. Do both of them thread into the catalytic converter or a connector that is removed as part of the process? Or is one of them separate from this job? Also, would it make sense to have them replace the sensors on the other catalytic converter (bank 1)? I'm going to show my ignorance here now, but does putting in two new ones with the new cat cause any sort of "imbalance" with the other two on the other bank 1 cat?


Also, if I have them replace the sensor, not sure what you mean here about hosing down the sensor. But I should still crawl under the car and spray any connections with PB Blaster to help them out?

There are two, one upstream before the exhaust air enters the catalytic, that is now known an an "air/fuel ratio sensor", it is more complex than a simple old-school O2 sensor. The second one is after the primary catalytic to measure the oxygen levels (rich or lean) and that's typically an old school sensor. So see? There are two. They switched to these many years ago to make the engine more fuel efficient. And if you want to get a Toyota sensor you can always check out Toyota dealers online for the best price, unless this local dealer is going to give you a good deal on one.

I wasn't able to see what year/trim of your Highlander that you have, so couldn't look up the exact catalytic from Toyota, but I looked up an 05 and it only looked like the air/fuel sensor was there in the catalytic that's mounted directly to the exhaust manifold.

And @Speedbird001 is talking about penetrating oil, just as you were going to do. But if the dealer is just going to take out the catalytic WITH the sensor, doesn't really matter it's not coming out anyway.

You could always save the old catalytic and take it to a scrap yard for $$$, those metals in there are high value!

 

[Snagglefoot]

Yes, replace them. Removing twenty year old sensors can be a real bear. Not worth the aggravation.

 

[97prizm]

Hi all,
I'm getting a catalytic converter efficiency below threshold error with my scanner on my Highlander. CEL is on. The dealer is pretty confident it needs a new catalytic converter but will still run diagnostics to confirm. I would think it would be prudent to replace both O2 sensors rather than transfer over 20 year old sensors but the dealer says they always just transfer over the old ones. Am I off base on this one? From what I've read, the old ones can be difficult to get out and may even be damaged. Car has about 130k miles by the way. Thanks for any input!

I had this happen with my cavalier earlier this week. Before you go and dump a bunch of money on new catalytic converters try running the fuel low, then a bottle of Techron complete fuel system cleaner and fill with premium. It cleared the code. I then got an evap code, so I replaced the gas cap. So far so good.

 

[97prizm]

They are worth replacing with the cat.




also this

Cataclean is worth trying first.

Maybe it was coincidence but after a bottle of Cataclean is when my cavalier started having misfires and fuel injector issues. Almost like it flushed out the injectors.

 

[John105]

I wish you luck as my first new car was a '98 Maxima SE, AND, I was about to do what you may be doing on our 2011 Enclave. It was a loss so I never got to replacing the CAT (rear bank) and the 2 02 sensors. We had the dreaded P0420, which first surfaced XMAS Day 2021. Upon reset it stayed away for almost a year. By 2025, it was coming back as soon as 28 miles.

If you are willing to pay the dealer, imho you'll be fine. Just that it's the most expensive alternative. On my LS430, my y-pipe rotted out (since my car was from FL it did so about 7 years after everyone else in the northeast). I got a nice mandrel bent aftermarket, and they transferred the 02 sensors no problem. The rears are wired under the carpet and to do the job right the seats could be removed otherwise carpet is slit open. So indie agreed you don't have a check engine today, let's reuse the 02s. But they did have to remove them from the old y pipe and reinstall. It's been 8 mos no problems.

Would you consider a non OE CAT, because ours was $2,100 each, and we also got a P0430 twice. I had gotten a Walker fed cat for $180. I get it is in no way no how as good as OE, but look at the price. I also heard the FED CAT may not be liked by the ECU. And, one is not allowed to install a FED CAT in CA, CO, NY, or ME (but you can smoke weed to generate tax revenue, go figure).

Does the dealer job fix the problem? I would say yes, as my fried had the exact same car and he let the dealer replace the CAT and 2 02's. It cost him $2800 in 2020, I think the job has not quite doubled for 2025. 4.8 hours labor.

I feel for you because I was about to do the very same thing just 3 months ago. What if the error comes back after all that work....

 

[Highboy]

And make sure they put in Denso sensors!!!

 

[50yr Street Mech]

The CATS failed in my 13' Pilot & 100k. Cataclean worked for about 4k, but had to keep dumping it in every 3 weeks. Gets expensive. So, I bit the bullet, had all 3 CARB CATS replaced with the 02 sensors. Used Walker aftermarket, much cheaper than OEM. Perfect fit. Took the tape off the dash covering the check engine light. Then I sold that RAT not too long later. Gas guzzlin monster !!! Nissan always had a problem with their CATS, especially the 6cyl ones. So, the dealer is probably right. For some reason, 4 bangers get more mileage on a CAT I've noticed.

 

[John105]

And make sure they put in Denso sensors!!!

I used Denso aftermarket front sensors in the LS430, no troubles in 3 years. Turned out to not be the sensors in reality, it was the wiring. This is why in theory one never replaces CATs, they last the life of the vehicle, one is supposed to find root cause. In practice, that can be a years long journey and also expensive. Replace yes is a parts cannon but what's the alternative, buy a new car and that's expensive too. But picture an Enclave/Traverse, is it worth putting $8k into CATS? when the vehicle is worth 7

 

[John105]

The CATS failed in my 13' Pilot & 100k. Cataclean worked for about 4k, but had to keep dumping it in every 3 weeks. Gets expensive. So, I bit the bullet, had all 3 CARB CATS replaced with the 02 sensors. Used Walker aftermarket, much cheaper than OEM. Perfect fit. Took the tape off the dash covering the check engine light. Then I sold that RAT not too long later. Gas guzzlin monster !!! Nissan always had a problem with their CATS, especially the 6cyl ones. So, the dealer is probably right. For some reason, 4 bangers get more mileage on a CAT I've noticed.

I learned when one goes to scrap a vehicle, first thing they do is raise it up and see if OE CATS. If not, they cut the offer in 1/2. As mentioned I got Walker for $187 when GM OE $2,100. But never got the chance to try it. Some folks insisted won't work to clear P0420, some said didn't fit, reviews were all over the place so very unpleasant scenario. Some said worked perfectly of course. A shop person said save your time and money won't work. I'm fairly certain that even though we went for 2 years clearing the code, our mpgs suffered. We got 10 to 12 mpgs at times all city driving. Even the Tahoe 6.2 cannot seem to go that low. It can get 14-15 under the same conditions.

 

[Arc]

Yes, replace them. Removing twenty year old sensors can be a real bear. Not worth the aggravation.

Pipe wrench is the only option. Of course there is always one that you can't get to that way.

 

[slacktide_bitog]

Thanks! You folks are the best! And funny too. @Speedbird001 ... single piece of matter! Here in Colorado, not a ton of road salt used and underside looks great but it just makes sense to me to replace the sensors as part of the job especially after reading some of the arguments here for it. One thing I'm confused about is that the service advisor (who says he used to be a technician) told me there is one sensor to transfer over, but the parts people (whom I've known for 24 years now and trust) said there are two - one they called an air fuel sensor. Do both of them thread into the catalytic converter or a connector that is removed as part of the process? Or is one of them separate from this job? Also, would it make sense to have them replace the sensors on the other catalytic converter (bank 1)? I'm going to show my ignorance here now, but does putting in two new ones with the new cat cause any sort of "imbalance" with the other two on the other bank 1 cat?


Also, if I have them replace the sensor, not sure what you mean here about hosing down the sensor. But I should still crawl under the car and spray any connections with PB Blaster to help them out?

One threads into the manifold/converter (this is probably the A/F sensor), and the other threads into a pipe after it.

Rock Auto has CARB-legal cats for your Highlander, so you don't have to spend too much at the dealer