Rattling my cage

General! We have fired the parts cannon and are out of ammunition! But the enemy is still advancing and seems to be in full force!

Simply block the egr flow to eliminate egr. Egr rarely causes misfires anyway and causes rough idle only if stuck open.

95% head gasket. Even without obvious coolant loss, with negative combustion gas in coolant and or with negative leak down test.

Dual view borescope is the weapon of choice.

 

If and when you do the head gasket, do a full EGR clean as well. See first two links in my signature (on a phone turn it landscape to see signatures).

 

were the 2015 models prone to HG failures? I thought that was solved by 2015 model year?

 

the theory goes that they got new piston and ring design, so less egr build up. but it still needs to be cleaned.
or if you believe toyota, it's a coolant pump software issue.
or if you believe some posters here, it's the 10k oil changes.
or if you believe the car care NUT, it's the acidic coolant and toyotas lack of coolant change recommendation frequency

 

Gasketmasters latest videos recommend preemptive hg changes on all gen3s and rebuilt once they blow (“in stock”).

Rebuilt gets you another 150k miles with a better hg (even from Toyota), better pistons, rings and probably the better intake and egr valve. There is no doubt the gen3 low tension rings cause oil burning or excessive oil burning which multiplies carbon buildup and preignition.

Many 2007-15 Toyota models including Camry, Corolla, RAV4, Solera, Matrix and Scion also were oil burners with low tension rings but only Prius and a low volume Camry hybrid had a thermal cycling Atkinson cycle engine.

 

Just editorial:

Gen 4 fixed the EGR system "shortcomings", but had the misfortune of Exhaust Heat Recover system failures, leaking coolant, this time just into the exhaust, but with protracted neglect could also lead to head gasket failure. More than a few were also misdiagnosed, mechanics seeing (EHR) coolant loss and changing head gasket.

Gen 4 press release, with "revised" EGR system mention, attached:

 

The press release does mention "new EGR system with cooler" as a bullet point. The gen 4 adopted a "catalyzed EGR" system, reflecting industrywide research that was being conducted and published during the gen 3 development years.

 

Translation: they connected the EGR system past the catalytic converter, instead of before it. Presumably with the aim of having less carbon in the system. They also more or less doubled the cross-sectional area of the cooler.

Just running a few of the prototype gen 3's, say for 200K miles, and they would have seen the excess carbon build-up in EGR system. And the runaway oil consumption due to "low tension" rings. And likely blown head gaskets.

 

The "translation" may not be necessary; the published engineering literature, which came from the research being conducted industrywide, kind of covers it.

Moving to catalyzed EGR changes the chemical constituents of the exhaust gas and changes its effects on combustion; that was a significant area of the research.

The increased cross-sectional area of the cooler and the rest of the plumbing follows directly from the lower pressure of the exhaust gas past the cat, and what cross-sectional area is needed to obtain the intended flow at that lower pressure.

I have not said anything here that Mendel hasn't seen before.

 

Still, 3rd gen EGR system will be near-completely clogged by 200K miles. 4th gen system with over 300K, just a light dusting*. That's engineering advance for sure.

* reported by @jerrymildred, from work experience at Tampa Hybrid.

 

There is no doubt “egr cooler cleaning” is unheard of before or after gen3.

Toyota management pushed their gen3 engineers to gain mpg while reducing costs. Result 1: the gen3 cat has less precious medals through the addition of a suspect egr system to maintain low US/carb state emissions. Result 2: New inverters failed without warning. Result 3: Cylinder cooling distribution was compromised. Result 4: Low tension rings to increase gen3 mpg while multiple other low tension Toyota engines beginning in 2007 had excessive oil consumption - including their flagship Camry which updated their rings in 2012.

Apparently some countries had no egr on gen3.

Interestingly the gen3 system was sold in other countries through 2021 in the v/alpha/+ without widespread reliability failures.

 

If the new egr valve was installed or the egr flow was manually blocked the egr is not causing misfires.

A head gasket intermittent leak of coolant into the cylinder is a well known problem with these engines.

Have your mechanic do a cold engine dual view borescope cylinder inspection with a manually pressurized coolant system. What he is likely to see is a steamed cleaned piston, possibly a drop or two of coolant dripping from the head gasket and maybe a scored cylinder wall. Any of those means a head gasket or a rebuilt engine is needed.

Car Care Nut HG Borescope at 7:40

P0420 is almost always a bad cat based on an automatic test that can judge the cats efficiency. The sensors have their own tests.

 

The seller knew all this. What craigslist flipper sold it to u

 

Yes, seen many 15's with head gasket issues. "But they had the reflash, updated intake and EGR and didn't burn oil".....so? 2016-17' Gen 3 Prius V and CT200h models don't seem to have the problem. Riddle me that, Riddler.

 

No, the P0420 will give a description on Tech Stream what sensor or bank it is, signifying upper/lower etc. The only time the Cat will be the problem is if you replace both sensors and it still comes back and throws that DTC. Maybe it's the APP or cheap auto zone scanner you all are using? Sensors are way cheaper anyway, why would you make someone buy a $2000 exhaust pipe w/cat before you diagnosed what tech stream says?

 

While the code, as rjparker said, is set by an automatic test that is meant to be specific to cat converter performance, and the sensors do have their own tests (which prevent this test from even running if they fail), it's also true that the cat test can be influenced by a whole range of things including sensor issues (not severe enough to set their own codes), leaky exhaust, even the EGR system, so there are troubleshooting steps worth working through before condemning the cat.

If I remember right, @mr_guy_mann has posted knowledgeably about working up P0420 in puzzling cases.

 

Tech Stream literally gives the description and/or sub codes to tell the tech where to look and what the actual problem is. Always take your car to a certified mechanic instead of wasting time and money.