Do I really need to replace the Catalytic Converter as well?

I brought my '15 Subaru Legacy (2.5i) to the mechanic to have him check why it would occasionally and momentarily ride rough. He discovered that I had a bad O2 sensor which is messing w/ my catalytic convertor that also caused a spark plug to fail which is resulting in 1 of the cylinders misfiring.

He tells me I need to replace the Oxygen Sensor, Spark Plug, and Catalytic convertor.

 

I'm curious to know if it's an acceptable idea to replace the O2 sensor and spark plug, but leave the original catalytic convertor? After a bit of conversation and teeth pulling, my understanding is that it's not blocked and that the O2 sensor is the root of the other problems.

Just replace o2 sensor and spark plug,I doubt your cat needs to be replaced.

I brought my '15 Subaru Legacy (2.5i) to the mechanic ... He tells me I need to replace the Oxygen Sensor, Spark Plug, and Catalytic convertor.

Just replace o2 sensor and spark plug ...

X2. A bad O2 sensor can cause a catalytic converter meltdown, but it doesn't have to be all-or-none, either. Just replace the O2 sensor and spark plugs (all 4 of them). The (expensive) catalytic converter can be replaced separately, if it proves necessary.

 

 

Edit: Your 2015 Legacy 2.5 is probably subject to Subaru recall campaign WUJ-95, in which case Subaru will replace the exhaust header/catalytic converter assembly at no charge. See attachment, and then see a Subaru dealer. Or you can go to this subaru.com web page and plug in your VIN. It's entirely possible that a crack in the exhaust bellows, causing the exhaust system upstream of the CAT to suck air, is the root cause of your problems.

Recall_WUJ-95_Exhaust_Manifold_pp_1-4.pdf

Edited September 25, 2020 by ammcinnis

Thanks for the info guys.

 

The mechanic just informed me that:

1. There's a small hole on the catalytic converter and air can be felt puttering out of it.

2. The O2 sensor is stuck in the catalytic converter.

 

Apparently the O2 sensor is the original and has been in the catalytic converter since day 1. It's now basically fused to the catalytic convertor. I guess this is why the mechanic said it needs to be replaced along with the O2 sensor and spark plug.

 

Though at this point, I'm thinking to have a car-head friend remove the O2 sensor likely breaking what already malfunctioned, then replace the sensor and then replace the spark plugs.

OR, and here’s a wild notion: do what ammcinnis recommended and take it to a dealer for the recall...

I find it very hard to believe that the o2 sensor is stuck and unable to be removed in a 5 year old Florida car. As mentioned, take it to the dealer, and have the wicked expensive cat replaced under warranty, the sensor is likely just fine.

Apologies ammcinnis. I got the email notification and read your and PATS4LIFE replies there before coming here hours later to respond. Needless to say, I totally missed your edit.

Either way, I forwarded the recall notice to my dealership's service department (honestly the new management is absolutely great). They reviewed it and gave me some insight.

Subaru is doing these recalls in waves. They're taking care of those currently in the northern states first, then working their way to the southern states. Thankfully I'm the second owner, the first owner was from a northern state, they're working on getting me in with the first wave to have the problem fixed.

Spark plugs would be on me, the Catalytic convertor and O2 sensor would be on them.

What is your mileage? If your spark plugs are even close to due, I’d do it. If they were already done, then don’t bother. Get your free cat and move on.

They reviewed it and gave me some insight. Subaru is doing these recalls in waves. They're taking care of those currently in the northern states first, then working their way to the southern states.

Your dealer should have already known that. It was explained on page 2 of the TSB excerpt I posted. The final "wave" was originally scheduled for September 2020, although COVID-19 may have altered the timimg somewhat. Your dealer should be able to take care of you pretty quickly.

 

Hint: Don't change the spark plugs until last ... after the new CAT and O2 sensor are in place ... otherwise the new plugs may quickly carbon-foul due to an overly rich mixture. Let us know how it goes.

Edited September 29, 2020 by ammcinnis

o2's are much easier to replace than a CC. I would start there first.

o2's are much easier to replace than a CC. I would start there first.

 

You’re too late to the party. Also, it’s not a very long thread for you to say it’s TL;DR...

Edited September 29, 2020 by gathermewool

I find it very hard to believe that the o2 sensor is stuck and unable to be removed in a 5 year old Florida car. As mentioned, take it to the dealer, and have the wicked expensive cat replaced under warranty, the sensor is likely just fine.

 

Agreed! That o2 should come out with no problem whatsoever! Even if it lived in the NE for 4-5 years, it would still come out easily.

I find it very hard to believe that the o2 sensor is stuck and unable to be removed in a 5 year old Florida car. As mentioned, take it to the dealer, and have the wicked expensive cat replaced under warranty, the sensor is likely just fine.

There are an abundance of posts of stripped threads coming out of new converters. Someone at the factory was clearly in a hurry. These are all from recalls. Either way the dealer has to "goodwill" the sensor and replace it free of charge.

 

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Very strange, thanks for the info, that makes sense that there could be issues if they were crossthreaded at the factory or something.

CONCLUSION: The dealership was able to use the recall to replace the catalytic converter. They were able to successfully remove the O2 sensor after soaking it overnight.

The spark plugs were not covered by the recall. The dealership offered to give me a break and offer a discount to change out the 4 spark plugs for almost $600.

 

Thankfully I live close to home, so I'm just going to buy 4 spark plugs and fix it over the long weekend myself. $50 for spark plugs and maybe an hour or two of work. $600 is just insane. Heck even $350 seems a bit high. I get having to move components, but are we really talking about 5-6 hours of work seeing as most mechanics charge about $90-100 per hour.

You still haven't answered how many miles and whether this will be the first plug change.

 

Have you had time to drive after the cat replacement? Are you experiencing any issues now?

 

If the plugs were already replaced at 60k I'd leave them alone.

$600 for plug replacement??? Yea, tackle that one on your own.