What's inside a Catalytic Converter?
Thread Starter
Lexus Champion
Joined: Aug 2012
Posts: 1,729
Likes: 132
From: Toronto, Canada
What's inside a Catalytic Converter?
I chopped open the catalytic converter on my Corolla to see whats inside and how it works. Here's a video:
The catalytic converter is located between the manifold and resonator in the exhaust system. Its purpose is to convert toxic gasses from the exhaust stream into less harmful gases.
There's an oxygen sensor behind it for the ECU to monitor catalytic converter performance.
Grinding it open:
Inside there is a honey comb shaped ceramic membrane coated with precious metals. That's what makes them so expensive.
The precious metals act as a catalyst, encouraging a reaction to occur from toxic gasses to less harmful gasses in two stages, reduction and oxidation.
The ECU controls the air to fuel ratio with the first sensor before the catalytic converter. It must be 14:1 for optimal combustion and catalytic converter performance. The rear oxygen sensor ensures enough oxygen exits the converter and that it is working properly. Otherwise you'll get a P0420 or P0421.
The catalytic converter is located between the manifold and resonator in the exhaust system. Its purpose is to convert toxic gasses from the exhaust stream into less harmful gases.
There's an oxygen sensor behind it for the ECU to monitor catalytic converter performance.
Grinding it open:
Inside there is a honey comb shaped ceramic membrane coated with precious metals. That's what makes them so expensive.
The precious metals act as a catalyst, encouraging a reaction to occur from toxic gasses to less harmful gasses in two stages, reduction and oxidation.
The ECU controls the air to fuel ratio with the first sensor before the catalytic converter. It must be 14:1 for optimal combustion and catalytic converter performance. The rear oxygen sensor ensures enough oxygen exits the converter and that it is working properly. Otherwise you'll get a P0420 or P0421.
Lexus Fanatic
Joined: Oct 2003
Posts: 94,696
Likes: 290
From: Virginia/D.C. suburbs
Lexus Test Driver
Joined: Sep 2016
Posts: 8,588
Likes: 392
From: PA
What's going on when there are 4 of them on a car.....(my 335i has 4)...that seems like expense and weight....
edit here's a pic, there are two more cats after the turbos....not shown
http://f30.bimmerpost.com/forums/att...1&d=1339722283
edit here's a pic, there are two more cats after the turbos....not shown
http://f30.bimmerpost.com/forums/att...1&d=1339722283
What's going on when there are 4 of them on a car.....(my 335i has 4)...that seems like expense and weight....
edit here's a pic, there are two more cats after the turbos....not shown
http://f30.bimmerpost.com/forums/att...1&d=1339722283
edit here's a pic, there are two more cats after the turbos....not shown
http://f30.bimmerpost.com/forums/att...1&d=1339722283
Lexus Test Driver
Joined: Sep 2016
Posts: 8,588
Likes: 392
From: PA
I've never had a CAT fail on me on any car, to include the Maxima being 19 y.o. (it has EGR issues, but not CAT, which is original). I've always felt like that's something you don't want to replace due to cost, and the questionable quality on replacements vs OE.....
Also I'm quite fascinated by the fake dual exhaust phenomenon..when did it start, late 80's? Who started it? I know in the earlier days, they were real, with straight pipes right out of the manifolds of a V8. Imagine that today, you can have dual exhaust on an inline 4? Which of course has nothing more than a y-pipe...also curious if an engineer had free rein, what would they design in this day and age, say out of a V8?
Also I'm quite fascinated by the fake dual exhaust phenomenon..when did it start, late 80's? Who started it? I know in the earlier days, they were real, with straight pipes right out of the manifolds of a V8. Imagine that today, you can have dual exhaust on an inline 4? Which of course has nothing more than a y-pipe...also curious if an engineer had free rein, what would they design in this day and age, say out of a V8?
Thread Starter
Lexus Champion
Joined: Aug 2012
Posts: 1,729
Likes: 132
From: Toronto, Canada
Lexus Test Driver
Joined: Sep 2016
Posts: 8,588
Likes: 392
From: PA
All the more reason I wouldn't trust aftermarket (I suppose this is just so you can pass emissions)....when things are "precious," human nature is to cheat. imho the incentive to not cheat on OE is warranty coverage. Put it this way, my 1998 Maxima has the original CAT, yes, but from the CAT back, it's had 2 exhaust systems. The original lasted 12 years on the car in the northeast. The Walker lifetime replacement lasted 30 mos. And nobody incl. Walker would honor the lifetime warranty (not gonna ship the system back to them for inspection lol). Now it has a 2nd Walker and some other muffler forgot the brand but powder coated black.....when they build shoddy exhaust parts, I can only imagine how they would treat CATS....
Trending Topics
Lexus Fanatic
Joined: Oct 2003
Posts: 94,696
Likes: 290
From: Virginia/D.C. suburbs
Gold, though, is usually reserved for the coating of air-bag-sensor components. That's because of gold's resistance to corrosion, and the Federal mandate that says that air-bags have to work reliably for at least ten years.
ClubLexus Stories
Celebrating Lexus & Toyota from Around the Globe
Lexus NX 350h: A Fuel-Sipping Secret Hot Hatch???
Michael S. Palmer
5 Best & 5 Worst Lexus Daily Drivers
Joe Kucinski
Top 5 Hottest Lexus & Toyotas in 2026 (Hardest To Buy)
Brett Foote
2026 Lexus IS 350 F Sport Review: The Last of Its Kind Still Rocks
Michael S. Palmer
Top 10 Most Confusing Things Lexus Has Ever Done!
Joe Kucinski
2026 Lexus ES Review: Lexus Re-Embraces Founding Principles
Michael S. Palmer
10 Lexus Bargains That are Cheaper Than a New Toyota RAV4
Joe Kucinski
8 Weirdest Things Lexus Has Ever Built
Verdad Gallardo
10 Lexus Designs That Have Aged Like Fine Wine
Verdad Gallardo
Thread
Thread Starter
Forum
Replies
Last Post
