Disappearing P0420 CEL after OEM muffler replacement

Hey consider self lucky many cannot get light off or code cleared. Mines been on 3 yrs theyres nothing else to replace.

 

If your CEL turned off "by itself" but a code is still present, it means that the ECM ran & passed the P0420 cat monitor test. Maybe the muffler work disturbed a leaking connection at the exhaust manifold. Maybe the cat test barely passed- and might fail again tomorrow.

Posted via the PriusChat mobile app.

 

I don't think the cat has really much to do with fuel economy personally I used to delete and gut cats way back in the old days in the '80s living in western Massachusetts and my car still passed the smog test which is a real tailpipe test and you had to have a number. And the number was always there The cat looked like it was in place there was nothing inside of that bulbous piece of metal was empty. The Prius runs the self test eventually that self test probably helps wear out the cat and then it falls below a threshold and now you have the code. Sounds like more of a sales tactic to me than anything else. Luckily I live in a state where they got smarter than that and we don't have to worry about the check engine light being on safety inspection only I never noticed any mileage changes with or without a cat though ever.

 

If all it took to fill the oil to the F mark (or at least somewhere in between the L and F marks) then your oil wasn't low enough to cause low pressure.

 

IDK what Blue driver did, but usually a green mark indicates that the ECM has run and completed a given monitor. Whether the monitor passed or failed is determined by the presence of fault codes.

Several kinds of failures can restrict exhaust flow through the cat and cause loss of engine power & mpg. Other things can "coat" the reactive surfaces inside the cat, rendering it ineffective without having much impact on flow.

A common problem is the oil control rings on the pistons. The engineers use low tension rings to reduce friction. When car owners go too long between oil changes or use low quality oil, carbon forms over time and "locks" the oil rings in place. That causes more oil to get into the combustion chamber then into the exhaust (increasing oil "consumption) which coats the cat surfaces.

PCV faults can cause oil control problems, but that happens far less often than stuck oil rings.

I haven't found any "goop in a bottle" that will (reliably) unstick the rings OR improve cat function. YMMV.

"Hopefully top it up?" Check the oil level. Have the car parked on a fairly level surface - engine off for at least a couple minutes. Pull the dipstick out and wipe it clean with a rag. Insert the dipstick fully and pull it out again. The oil should cover the end of the dipstick - ideally up to the top "range" mark.

It should never get low enough to go below the bottom mark - or so low you do not see any oil on thr dipstick at all.

If it is low, you need to set reminders on your smartphone to check more often (and change oil more often - 18 months is way too long).

Posted via the PriusChat mobile app.