P0420 code on 2006 Prius

I bought a 2004 Prius in January, and after a couple of months the CEL light started coming on. I took it to the dealer, and they told me it was the catalytic converter. They say it's a $2000 repair (the part alone is $1500). They say the car will drive fine with it, but it probably won't pass the emission test (in the Atlanta area, you have to get your car's emissions tested every year to get your tag). The car already passed the test this year before I bought it, but I'll have to get it tested next year. I figure I have a year to decide what to do. If they don't have emissions tests where you live, it may not be an issue.

Now I understand why the seller sold the car to me at $2000 less than the blue book value!

 

The engine ECU logs DTC P0420 after evaluating the signals provided by the air/fuel ratio sensor which is upstream from the catalytic converter, and the oxygen sensor which is downstream. It is possible that if you replace the air/fuel ratio sensor, that may provide a sufficiently improved signal so that the engine ECU will no longer log DTC P0420.

Since the A/F ratio sensor only costs $150 or so, it might be worth replacing prior to stepping up to a $2K repair.

Another alternative is to ask a muffler shop to install an aftermarket catalytic converter for several hundred dollars. However the expected life of cheap aftermarket is much shorter than original equipment.

 

Just curious Patrick but, is there a after market sensor out there that may be 1/3 the price? Hal

 

Hi Hal,

There might be, but I personally wouldn't use aftermarket for this critical function. The idea here is that we are trying to avoid replacing the catalytic converter, so we want to install an air/fuel ratio sensor that quickly responds to changes in oxygen content.

 

Some folks are cold to the idea of Bosch O2 sensors, but they do offer OEM fitment (important) and they are cheaper, but not 1/3 dirt cheap, more like 2/3 to 3/4 of the mail order price from an online Toyota parts counter.

Aftermarket cats carry a 5 yr/50K mile warranty typically, with an installed cost of about $500. In California, a factory replacement is the ONLY option.

 

Thanks, I`ll try replacing the A\F sensor.

 

What was the outcome? I have the same error code and am just starting the process.

 

How many miles? The cat is covered to 80,000. FYI, the forward O2 sensor (A/F) is not as easy to change as it is on most cars.

 

Hi guys! I've been searching forum to find the solution for the same problems as posted in this thread. I have a 2005 prius, 136k. CEL came on 2 weeks ago. I bought scanner and it showed p0420-cat converter. I checked for any visible damage on the cat or exhaust leak anywhere. None found. Then i cleared my cel and drove the car for about 70 miles. I scanned it again and found my O2 sensor and my cat converter had readiness-green light on both, ready to pass state inspection. Only segment not ready on my scanner was EVAP system. So i went for inspection and got new sticker even though evap wasnt ready. I guess its fine if only one component is not ready as long as that component is not cat converter. At that point i thought that cel was just a one time scare. But 2 days ago i got cel again. I scanned it and i got the same code again-P0420. Hmm strange. So i repeated process of clearing the light and driving again and i had readiness on cat and O2 just like before but my evap wasnt ready again. So my question is: what is the possibility of something in the evap system triggering the cat code? Evap is the only segment never getting readiness and after 70 or 80 miles of driving (after being cleared) it triggers cat code? Is that too much to hope for? Or my cat is on its last days before its completely shot?

 

If you clear the CEL, then all monitors go to incomplete.

I believe you need to clear the CEL then let the car sit for several hours, and then take an OBDII trip, before the EVAP will set as OK.

It is probably the cat.

 

I was getting the same error on my 2005 prius. I went to a local muffler shop to replace with an aftermarket cat converter. It cost me around $220 and the error code was fixed and was able to do the smog test. I've had the aftermarket cat converter for over 6 months without getting the error back.

 

As mentioned, P0420 is sometimes thrown after oxygen sensors get old and degraded. If you eventually have to replace the cat, they'll likely put in a new after-cat O2 sensor anyway, so it wouldn't hurt trying that sensor first.

Usually, the EVAP monitor takes a couple of cold soaks and drive cycles, with a medium-full fuel tank/bladder. This requires several days.

 

I had the CEL light come on my 2005 Prius with 113k, 1000 miles from home in Louisiana! Stopped at first auto parts store I could find. Code P0420. We were on vacation, kinda freaked us out. They cleared the code and we drove another 100 miles to our destination. CEL came back on during that leg.

I googled the code and and the plethora of responses really freaked me out. I thought for sure our vacation budget was destroyed. Thanks to dumb luck I stumbled into the Meineke in Lake Charles Louisiana.

The manager was "Prius smart" and charged me $20 to test the cat converter to see if it was clogged, it wasn't. He recommended a can of seafoam to try to clean out the fuel system. What the heck, $8 beats $1,600.

It worked! CEL went off and we enjoyed our vacation. The CEL comes on intermittently, I just put some seafoam in the tank and it disappears. Since I know the catalytic converter isn't clogged I don't sweat it, it's been 5k miles.

 

My wife's 2008 Prius had the check engine light come on a few weeks after we purchased it and I suspect it was intermittently coming on before it was sold to us. PO420 was the main code, but others came on as the CEL came on more often. I also have a 2008 Prius that I bought recently and tried switching the MAF Sensor, but no dice. Then I read about the downstream O2 Sensor sometimes needing replaced. I pulled it out and cleaned it with MAF Sensor cleaner. The light hasn't come back yet after over 100 miles of driving. I may be on to something because in the last month, I've had to clear it many times and it had always come back after a few short trips. I may end up needing to replace that O2 Sensor, but for now, progress! BTW, her Prius has 329,000 miles and runs amazing outside of the annoying CEL. We usually get around 50MPG in warm months and the monitor is extremely close to what the tanks calculate in mileage.