P0420 and P0430 at the same time

Hi,

I have P0420 and P0430 in my Lexus RX400h (2008). I replaced MAF sensor already to brand new. The difference between cat temperature on both banks is more than 160C (320F). I have freeze frames when the code appears but can't see anything suspicious. The STFT is about +/- 4% and LTFT is about -1% on both banks. The engine temperature is 81C (is it not too low?) 177.8F. No other symptoms, the car drives smoothly no issues during acceleration, no rough idle. The front O2 sensors have amplitude +/- 3.5V and rear sensors I can't notice any behavior such 'copy' of the front sensor. The voltage drops in rear sensors to 0.1V sometimes and then the errors are thrown but can't glue in what conditions it happens. One thing noticed that when drive the car after night when it's cold then the errors are thrown just after 10 minutes drive. When I clear the codes and continue driving for example 200-300 miles then codes not appear during the same day. I tried different variations also tried using the same journey but no codes. But as I mentioned before early morning when the car is cold I drive on motorway and after 10 minutes drive even less the codes appears again.

Attached screenshots of the freeze frame.

Appears converters just losing efficiency after 11 years.

SlyCom wrote: The difference between cat temperature on both banks is more than 160C (320F).

I think you're looking at a difference in temperatures between the upstream and downstream sensors? And not bank-to-bank.

Anyway, I dunno that I'd read too much into these PIDs. :silly: There's no exhaust temperature sensors, so these PIDs are calculated. If it helps, I checked a couple other Toyota/Lexus vehicles of similar years, and they all show the upstream sensors a few hundred degrees hotter than the downstreams.

One thing noticed that when drive the car after night when it's cold then the errors are thrown just after 10 minutes drive.

...

When I clear the codes and continue driving for example 200-300 miles then codes not appear during the same day.

It's very likely that you're completing the entry requirements for the Catalyst monitor when you drive the vehicle when it's been allowed to sit overnight. Once the engine is warmed up and you clear the codes, you may not complete the entry requirements for the rest of the day.

You also end up resetting all the other monitors when you clear the codes, like the O2 Sensor and O2 Sensor Heater. It's my experience that Toyota/Lexus products are very specific about when and how they complete the O2 Sensor monitor - and the PCM is likely programmed not to complete the Catalyst monitor until the O2 Sensor monitor passes. Make sense?

Unfortunately, I gotta agree with cj1, it sound like your cats are done. Because you know your trims are good, there's only a few checks left. Make sure your engine isn't burning oil (unlikely), and make sure there's no exhaust leaks ahead of the downstream sensors. I see no TSBs related to cat codes on BBB Industries.

It may be worth a call to your local Lexus dealer? Hybrid vehicles like this sometimes have extended emissions warranties that'll cover cats. Worst thing that happens is they tell you no! :silly:

Thanks for reply. Is it worth to replace with aftermarket cats? I wonder how it's possible that two cats become bad at the same time. I understand if there were any issues with the engine and it could destroy cats but I never had any issues.

Really sounds like a goosed cat, using temperature measurement can be thrown by the shape of exhaust system causing a hot spot.

Keep in mind a P0420 can be caused by lack of activity on the post cat sensor as well as following the front sensor.

The test for a cat lcode is normally only carried once the engine is close to normal running temperature.

I doubt two front or rear sensors are bad at the same time. I always thought that petrol engines are more reliable than diesel Never had any issues with diesel cars.

SlyCom wrote: Is it worth to replace with aftermarket cats?

Nope! :lol: Not if you intend to keep the car, anyway.

I've been round and round several times with aftermarket cats, and rarely found one that held up over the warranty period. Almost all came back within a few thousand miles with another cat code. Swapping the cats multiple times will also be time consuming in your case, since the catalyst is coupled with the manifold.

What about new but not original one? Like sold on eBay or Amazon.

Since the hybrid battery is out of warranty and probably close to needing replacement doesn't make sense to spend 2-3 thousand dollars to replace cat converters.

Maybe try to clean cats or off set rear sensors.

Check the exhaust system for leaks. If there is a small exhaust leak just aft of the down stream O2 sensors it can throw a code. I'm not familiar with this car. Just after the cats, is there a Y pipe? Maybe it's leaking. The leak does not have to be big.

I don't know about the US but in the UK the scrap price of an original factory cat isn't that far below the cost of the cheapest aftermarket replacement, that must say something about the lack of quality of most aftermarket cats.

Some guy from the service made a visual and sound inspection (engine working) of the exhaust and said there are no leaks. The Y is after sensors. Can a leak after Y generate P0420 and P0430 ?

Should I try replace sensors and see difference?

SlyCom wrote: Some guy from the service made a visual and sound inspection (engine working) of the exhaust and said there are no leaks. The Y is after sensors. Can a leak after Y generate P0420 and P0430 ?

Yes an exhaust leak within 24 inches after the downstream O2 sensors can trigger P0420 and P0430 codes. A flex joint in the exhaust system sometimes only leaks when the power train is under load as the engine twists on it's mounts. Worth checking in my opinion.