4th Gen DIY heat exchanger bypass solution

And if it’s an emissions thing, why not just extend it to 150k for all 50 states. Like the air doesn’t move from the “approved” states…

 

CARB states with big diesel trucks is a mandatory 350,000 mile warranty on emissions parts.

 

What years did the heat exchanger issue affect? Was it only the early Gen 4 models?

 

I bet that it's going to be all of us, or at least up to 2022 models. It took them that long to recognize it as a recurring issue.

 

Just wanted to pop in and thank you for this thread and notes on this problem and the bypass fix! Due to my relying on the car, I couldn't wait for amazon to deliver the hose in a week. I was able to find the Gates 18777 at my local O'Reilly's store, but ended up using a Gates 18701 hose as it has a little more length and flex room.

I also faced a little trouble in refilling the coolant reservoir, after driving a bit it kept appearing to drain itself completely, but turns out it was trying to cycle in the new coolant. Ended up taking a few refills, and working to burp the radiator to get everything topped up correctly over a couple hours, but it does seem to be going now correctly without leaking

Don't know how, or if I'll try to approach Toyota about fixing the TSB as I'm pushing 115k miles, but in the mean time at least if someone does decide to steal the cat i can still drive.

Anyways, thanks again for your post, TexasDriver!

 

Did the bypass cause the check engine light to ever come on or store come temperature related fault. There is a temperature sensor at the pipes coming in/out of the heat exchanger I was thinking if the engine module does not see the coolant a certain temp coming out of the heat excnahger that it may set a code ?

 

I'd like to think he would have mentioned that. I'll let you know as I just completed this bypass on a 2017 Prime.

 

Actually, I think he said it sounds like a…bong (as in rhymes with Cheech & Chong).

Anyway, this whole thread has been very enlightening. I’d be horrified if I saw huge clouds of steam and coolant coming from my tailpipe. At least there’s a low cost workaround.

 

After installing the bypass, the huge clouds were present until the remaining coolant burned off. even driving spirited the coolant temps are where they should be.
Question tho... Gen 3 you would get all types of false positives with engine codes before uncovering the root cause of an issue. The dealership told me Gen 4 is not the same as Gen 3 in the sense that now codes mean the codes that are displayed. So when I saw the
P148F-00 code I almost went to replace the water pump before reading about the heat exchanger being an issue. So after the bypass, I didn't clear the codes, the car isn't running hot as an indicator of a bad pump. Can someone confirm if the display and meaning of codes on the Gen 4 have improved?
I'm having them replace the heat exchanger under warranty now, something tells me if the codes are cleared I shouldn't have that water pump code, right?

Also, I learned Toyota will not cover a rental or loaner car since the service hours do not exceed 8 hours.

 

Setting up to do the bypass after work today myself, wondering if the issue of not having a dealer provided warranty on my car will cause any issue for them taking care of it for me? Assuming I will have to pay the $175 diagnostic testing they need to do before doing anything with the car, just not sure if will then try to charge for having parts replaced due to not having a warranty on the car, 2016 with ~52k miles.

 

If the reports of many dealer repairs here at priuschat are any indication of what to expect given the situation you're describing, I'd suspect the answer to your question is - they will probably want to charge for parts and labor to repair the heat exchanger on your 2016.
Unless your car meets all the requirement listed in the TSB
https://static.nhtsa.gov/odi/tsbs/2019/MC-10166037-9999.pdf
And it will not be a bypass from a Toyota Dealer, it will be a full heat exchanger repair.

 

A trouble code always means, no more and no less, what the words say in the "DTC Detection Condition" box midway down the first page for that code in the repair manual. No different in Gen 3. If a person saw the code and jumped to some other or more specific idea of what it meant, and then it turned out not to mean that, can't blame the car or the code for that.

A P148F or P148F00 is set when the observed water pump RPM is unexpectedly high. What could make the water pump turn unexpectedly high RPM? Anything that means its motor is doing less work moving coolant around. So ... sometimes that's because the pump impeller broke, and now just kinda spins and doesn't move coolant around. But another reason can be that the coolant isn't there, because it leaked out the heat exchanger, and the pump is spinning without it. Can't blame the pump for that.

That's no doubt why the T-SB-0135-19, talking about heat exchanger leaks, does specifically mention the P148F00 code.

 

Yep, it was the heat exchanger and the pump was all good, working as expected.

 

Understood - and while I dont have a dealer warranty on the car I am not sure if this means it would be covered without that. The car is a 2016 with 52k so it should apply to the Toyota Emissions warranty, as well as within coverage on the California emissions warranty as I am in one of the states called out in Oregon.

"APPLICABLE WARRANTY  This repair is covered under the Toyota Federal Emission Warranty. This warranty is in effect for 96 months or 80,000 miles, whichever occurs first, from the vehicle’s in-service date.  Warranty application is limited to occurrence of the specified condition described in this bulletin.  For 2016 and 2017 model year Prius and 2017 – 2019 model year Prius Prime vehicles, sold, registered, and normally operated in California, Connecticut, Maine, Maryland, Massachusetts, New Jersey, New York, Oregon, Rhode Island, and Vermont. The California Emissions Defect and Performance Warranty"

 

Or more precisely it was the loss of coolant, and therefore the pump was overrevving—which is as expected, for that situation.

 

all truth in your words ChapmanF

 

Does anyone has that TSB for Canada? Basically regarding the warranty section. I don't have an issue with mine but contacted Toyota Canada regarding under which warranty the exhaust heat exchanger comes into and that's what I got for an answer

"We would like to direct you to the Owner's Manual Supplement under Warranty, pages 10 & 11, which lists what is covered under the Emissions Warranty"

From this video

The engine block is cooled after going through the exhaust heat exchanger. Meaning, if there is not enough coolant making its way to the engine, it will overheat and since the engine temperature is taken at the coolant level, you won't know that the engine is overheating until you get the water pump over revving trouble code, which means there is no coolant going through the engine for some time since the reservoir is now empty

 

Well, the cooling system is a closed loop, so depending on where you put your finger while you're talking, the coolant goes through the exhaust exchanger before the engine, and also goes through the engine before the exhaust exchanger.

The important thing is if it's leaking out of the system, anywhere, then eventually there won't be enough in the system, and the engine might overheat, and there might not be heat in the cabin, and the water pump might overrev.

 

Yes, usually it's a closed loop, but not while it's leaking through the exhaust system and if you look at the video starting at the time stamp I linked in, it specifically says that the out of the exhaust heat exchanger is the in to the engine block. If you leak coolant into the exhaust at that point, it's not making it into the engine block, which is what my previous post refers to.