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Hey everyone, I need some help. I recently bought a 2008 tundra with the 5.7 and today I got the famous ( or so I heard ) P0420 code. I am the second owner and the truck has 160k miles on it. The only upgraded part I see is the TRD cold air intake. I drove 20 miles to the store (mostly highways) and when I was finished shopping I started the drive home and within 10 miles I noticed the check engine light. I read that it could be due to a dirty air intake filter, a bad MFC sensor, a bad O2 sensor, or a back CAT. Now which is more likely the cause? I haven't noticed any power loss or bad smells while running the truck since the code and the dealership I got it from should have run emissions on it ( they said they did at least ) so it couldn't be that the CAT is bad right? It would have failed emissions. I will appreciate any help, thank you in advance.
 

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Couple of things.
First off, do some reading. The more you know the better the decisions you will make. So read through some of these below.
Secondly, if you do start replacing parts, start with the most obvious, cheapest and easiest first. Cat is probably the last thing you would want to look at.
Crawl under your truck. Look for obvious signs of issues. Something as simple as a hole in the exhaust or damaged 02 wire could cause a code.
And lastly, if you do find and fix the problem post back what it was. Forum websites suck because so many people come on with problems but never post up solutions. So you end up with tons of dead end threads.

 

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Yep, I'll piggy back on what these guys are saying. I've had these codes & usually it's just an O2 sensor. My truck has 2 on each side: up & down stream (2002 V8). Getting a bluetooth OBDII reader's worth the money, as it'll tell you exactly where the issue is (usually) for these errors - at least which O2 sensor or if it's the MAF. My last time I had to replace the front driver's cat, but it had a huge dent in it for about 2 years before it finally went bad. Plus I have ~310k miles on it, some of them on hard off-road terrain. Mine never seemed to go into limp mode, though.

Also, to answer your question: When they go bad, they just go bad. Their time's up. It can happen at any time. If the dealership said they ran emissions, they probably did. Definitely try to whittle down what's wrong with the OBDII sensor first - most auto parts stores will run it for you for free too, if you don't want to buy the reader (totally worth the money, imo).
 

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Chances are you have a bad O2 sensor, Bank 1 upstream. I would replace both upstream sensors. Use penetrating oil, more if you live in a rust prone area. If a sensor is hard to remove, take it to an exhause shop and have them flame wrench the bung to save the threads.
 

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Hey everyone, I need some help. I recently bought a 2008 tundra with the 5.7 and today I got the famous ( or so I heard ) P0420 code. I am the second owner and the truck has 160k miles on it. The only upgraded part I see is the TRD cold air intake. I drove 20 miles to the store (mostly highways) and when I was finished shopping I started the drive home and within 10 miles I noticed the check engine light. I read that it could be due to a dirty air intake filter, a bad MFC sensor, a bad O2 sensor, or a back CAT. Now which is more likely the cause? I haven't noticed any power loss or bad smells while running the truck since the code and the dealership I got it from should have run emissions on it ( they said they did at least ) so it couldn't be that the CAT is bad right? It would have failed emissions. I will appreciate any help, thank you in advance.
get you a bottle of cataclean and then fill your tank with 93 non eth.
 
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