P0420 is it always a bad cat?

Hello fellow Tacomaers,

So basically I have the CEL illuminated for a p0420 (cat operating below threshold) hard code, also side note:
Pending codes:
P0440- evap malfunction
P0441- evap incorrect purge flow
P0446- evap control circuit malfunction

All these codes came up together after replacing upstream O2 and disconnecting/reconnecting the battery.

What I'm wondering is if anyone has had experience in which a p0420 code didn't turn out to be a bad catalytic converter.

I am addressing the EVAP codes separately as that's a whole other can of worms, will have a smoke test done and determine what's going on there. VSV seems likely but with evap leaks who knows.

Unfortunately most of the threads I've been researching are a few years old and the [op] never updated what the result was.

 

Check for exhaust leak

 

Wow those were like my exact codes when I first bought my truck. Mine was a bad cat, but it can also just be the sensor. Can also be MAF related but usually that gives other problems.

 

I will be putting my shop vac up to the tailpipe and spraying it down with soapy water.

 

What did you end up replacing the cat with, oem or aftermarket? There is already an aftermarket cat on there now that is relatively new.

 

The down stream sensor is the one that will trip the PO420 code not enough variation in the signal .

Many times a leaking exhaust gasket will trip that code.

 

Magnaflow - was cheapest at the time and I'd heard the name before. I've had no issues with it, it's probably been 7-8 years

 

I replaced my cats with 50 state Magnaflows as well. About 6 or 7 years ago, but I do suspect they are going out (catalyst monitors are taking forever to reset). Might be something else though.

They were $600 installed at the local exhaust shop but that was in 2017...I'm sure that price is quite a bit higher now, but still cheaper than OEM. If you need to pass smog I wouldn't chance it with cheap aftermarket cats. They'll have less of the expensive metals in them that filters the emissions, more likely to not satisfy the o2/ECU and toss a P0420 again.

 

my magnaflow was $200 installed, no Cali tax

 

I honestly think it's easier to get away with that here than most people realize, when I go in for smog they never get under it to look at the cats and make sure they're "50 state legal"...its not like there's any marking on them to indicate it anyway. Probably could get away with it, unless you have an '99 or older where they do the sniffer test...exhaust readouts would probably be different. But for 2000+ years they don't do that test.

 

I honestly think they probably just have a database of registered cats, I don't think the emissions would be distinguishable from the worst OEM one. The only real difference is you need 2 in Cali

 

Any Truck with the California Emissions package needs two cats .

They were shipped all over the country .

 

Think they all started coming with 2 cats after a certain year...I'm not sure which. 98 or 99, maybe earlier?

they won't fail you for having just one cat if that's the way the vehicle was manufactured. You'll probably just get a notice with your registration every year asking if you'd like $500 to junk your "gross polluter" lol.

 

It doesn't even make sense, it's not like the exhaust pulses travel slower and/or make more contact with the catalyst . It's like the dual electrode spark plug - it would just mean they last longer

 

My Tacoma is a 2002 And it has two cats.

 

My '98 3.4 had 1 cat. My present '04 has 2 cats.

My '98 never threw a code in 300k miles.

My '04 throws a code every 200 miles. We don't have emission testing in Michigan, so I just reset it with my Scan Gauge.

In 100,000 miles, there has been no issue with drivability. The cats are just fine.

 

I could be wrong.....but the ones in later years they removed the egr system...

when they did that, a second cat was needed to pass all emissions.......cold and hot....

At least on the 4 banners.....dont know about the 5vz's .....

 

What is your goal here, fix the truck, get rid of the P0420 code or just drive it with the light on.

 

It has to pass emissions testing in the next week so code has to be gone and issue fixed. I can just erase the code but then all the drive cycles I've been completing will be gone also and by time I complete them again the code could just get triggered again.

 

this was the case with mine, very happy to just buy a new sensor, put it in and the code hasn't come back (2 years). ymmv of course but this was a great first thing to try