P0420 Catalyst System Bellow Threshold Bank 1?

The ECM uses both the upstream and downstream sensors, and control of the engine mixture, to test the effectiveness of the catalytic converter, and report this code if that effectiveness has dropped below threshold.

So the code is usually about the catalytic converter—that's the purpose of the test and the purpose of the code. Cases where the problem turns out to be one of the sensors just used for the test aren't impossible, but jumping there as a first guess would be like shooting the messenger. There are individual trouble codes for both sensors that are likely to be set if those aren't shipshape.

 

The catalyst monitor test is fairly complex and requires a number of functional systems in order to be accurate.

Replacing parts based on assumptions can: get expensive, not fix the problem, and cause new problems. (you might get lucky, but it's your money)

When I diagnose a P0420, I make sure - 1) there are NO exhaust leaks anywhere at or upstream of the converter, 2) both A/F (S1 - upstream) and O2 (S2 - downstream) sensors can accurately report full lean to rich range, 3) the engine runs properly (total fuel trim is 0 +/- 10%, and NO misfires) 4) there are no applicable service bulletins (TSBs)

IF all those are true then the car needs a new cat.

5) if the engine uses-burns lots of oil - that killed the old cat and will kill a new one as well.

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Follow the recommendations to find the causes of this code.

https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/repair%20manual/04pruisr/05/2054m/cip0420.pdf

 

You're wrong about everything you said for reasons you don't comprehend.

 

Find a competent shop to T/S this before you just throw parts at it. That's my friendly.

 

The system is actually very simple, but you need test equipment to T/S. Best wishes...I'm off.

 

1. Does your engine burn oil?

2. Have you checked the values produced by the monitor?


3. The aftermarket sensors can be a problem with bad quality. However I have used a Bosch aftermarket O2 on a gen2 after the cat and downstream sensor was stolen. The Bosch has different wire colors so read and follow the instructions. However as indicated above, a bad sensor or wiring will usually have its own code.



4. The odds are 95-98% your set of cats are bad. If it's oil clogging your mpg and maybe driving reliability is at risk. After spending (wasting?) money on sensors you can get a new set of cats. Assuming you are in a non-CARB state, an aftermarket gen2 set of cats that works is a Walker 16337 ($160 - $271).

 

How much oil does it burn, and did u use diesel grade oil?

 

You need to top it off and drive 500 miles. Then check dipstick. Many of these burn oil at high miles which can clog cats.

You have to unbolt cats at exhaust and cut them off downstream. Some have clamped the new cat to the cut side - most would have it welded.

 

My 2009 with 150k have this. I tried Liqui Moly Catalytic System Clean and it went away. But it came back after 1-2 fill ups. It was burning like 1/4 qt with 2-3k oil changes. This time i added Auto-RX engine cleaner with a NAPA brand synthetic oil. So far after 1k miles oil level hasn't dropped. Also the frequency of the the P0420 has reduced. Not sure if the warm weather helped or the cleaner helped. Previous history i could find was not great. Irregular oil changes and regular oil was used and was done at quick change places.

I never had to replace the cat. Rock Auto have it for decent price. But have to cut it and tie it with clamp. Seems not difficult. I may do it in the near future if needed.