P0420 (Bank 1) - Front or Rear Cat?

I'm pretty sure I need a new catalytic converter because I got the P0420 code from autozone and my 2002 Toyota Tacoma 2WD 2.4L EFI DOHC 4cyl runs sluggish on the highway and takes a while to come up to speed. This is the only error code they got.

However, the person behind the counter told me I needed the REAR catalytic converter, and when I asked them about it on their websites live chat they said I need the FRONT catalytic converter.

I tried googling it and can't find more information about it so I thought I would ask on here. If I'm getting a BANK 1 code, do I need a front of rear catalytic converter?

 

The code comes from the O2 sensor behind the front cat. So apparently it is bad based on O2 readings before / after. but that doesn't mean the back one is not bad also. An engine vacuum test can help at least show that a cat is becoming plugged, but it is not so easy to determine if it is just one. You could just disconnect the exhaust at the manifold and take a quick drive to see if it runs normally again. That honeycomb stuff inside can crumble and block the exhaust, building up significant back-pressure that robs power.

 

There is not a way to tell with the code which one is bad if it's bad because you have an Air/Fuel sensor before both cats and a Heated O2 sensor behind both cats. I would have someone with a scan tool check it out first because cats don't just go bad under normal conditions. You may have another issue. You may want to check your plugs and wires because I know the Autozone scan tools normally only show the hard fault codes. I have had my 98 2.7 almost die before it set the light. One time I had this code was when I put a clutch in and the gasket for the exhaust didn't seal well because it was a piece of crap and the exhaust leak caused the numbers to be off. I would look for the root cause before throwing in cats because sometimes when you fix the acutal problem the code will go away.

 

Do not listen to what someone making $9/hour behind a counter says!!!


If your truck has 'two' catalytic converters, as it is most likely a California-spec truck (most tacoma were, even outside of Cali). Both are three way catalytic, but small ones, too small for a single to scrub the exhaust enough to meet Cali standards.

I will defer to someone to suggest a way to test these individually without drilling a hole and sticking a probe in between the two. Though if youre getting P0420 codes, at least one is going out. Its most likely the first.

 

I'm hardly a "cat pro". But the only failures I have seen happen when the honeycomb crumbles. Commonly caused by something bad going through the engine and coming out the exhaust. Overly rich will do the trick as cats don't like raw gas. Dumping various kinds of "engine/injector/throttle-body cleaners will also do the trick. Hard to do nowadays, but a little leaded gas will ruin them quickly. Had this happen to me back when we still had leaded/unleaded and all I could figure was the gas station I used got the fuels mixed when they were refilling their tanks one day. A v8 started to feel like an anemic four. Vacuum test showed very little vacuum due to the back-pressure. I simply removed the thing back then to solve the problem, which also let me run normal leaded gas which was cheaper.

Usually when they start to go, an ECU code is the least of your problems...

 

Don`t forget this P0420 code is the ECM telling you that the The signal the ECM is seeing says the Efficiency is below the threshold value .

This can be triggered by a exhaust leak between the 2 sensors .

While the O2 sensor code does not trip the back sensor can still be bad.

After Market cats seem to drop below the threshold valve much faster the the Toyota Cats

 

I got the same p0420 as you after replacing the rear O2 sensor which was toast after 240k miles but I still get the code coming on. I got a scan reader and have been monitoring the live data and seems all is where it should be. I will reset the check engine light and sometimes I can go 300+miles before it comes back on and sometimes less than 50 miles before it comes back on,i also have on the original exhaust but it seems that there are no leaks. my truck has almost 250k miles now so I really don't want to invest in trial by error parts replacement think I can get thru state emmissions because sometimes I can go thru the drive cycles to where all computer IM checks are good on the scan guage its really a annoying code to track down and could be costly to fix with cat replacements. thinking about using this around inspection time,it has some good reviews by folks on this site in their trucks got a bottle for $20 if it gets me thru inspection then its well worth it. Heres a good thread about reading o2 and A/F sensors https://www.tacomaworld.com/threads/understanding-o2-signals-and-fuel-trim.259164/