Advice Needed! P0401, P0300, P0301, P0303 Head Gasket and/or EGR?

Prius 2010 Base; 188K Miles. Bought with 80k Miles from original owner for cheap because it had bad/noisy wheel bearings. Replaced front struts last month. It has been using some oil lately (less than half a quart every 6 months). Other than that, no issues whatsoever.

We were going on a camping trip 100 miles north (uphill). 40 miles out I noticed a red light flash for a few seconds on the dashboard, asked my wife to look it up (never seen a red light on the dashboard before). I decided to pull over just in case and I'm glad I did, it was the high temperature warning light. As I slowed down to park on the side of the freeway I noticed the CEL turn on for a few seconds. No other problems besides the lights at this point.
Once safely parked at the side of the freeway I let the engine run for a while before turning it off to check the engine bay for any issues and double checked the fluids. Nothing seemed off, oil, coolant and break fluid levels were all fine. Looked under the car for any leaked fluids and nothing, just condensation from the ac.

Started the car again and as soon as the ICE turned on the car started shaking really bad. Decided not to risk it and got it towed (flat bed) back home. I checked all fluids again and they are at the normal level. Turned the car on and it wasn't shaking any more, no warning lights either. I started driving it around the block and as soon as I started accelerating it started to shake again and the CEL started flashing so I turned back and parked it on the driveway where it is waiting to be repaired.

When I was troubleshooting the issue that turned out to be faulty struts/shocks I read a lot about the EGR and I was planning on taking out the EGR components in November (when the weather is nice here where I live) and giving them a good clean. Now, I'm not sure if the head gasket needs to be replaced so I turn to you guys for help.

1.- I'm leaning towards a bad heat gasket and a clogged EGR system, just a clogged EGR system or a clogged EGR system and bad MAP sensor. Would you guys agree? Am I missing any other possible causes?

2.- What would be the best (most definitive and easiest) way to know whether the head gasket is leaking/bad? Not sure I want to fix a bad head gasket, might just replace the whole engine or sell the car for parts.

3.- If it was your car, what steps would you take in finding the fault? (I pulled the codes in the title of this post with my friends scanner, planning on buying an Autel AP2500 tonight).

Thanks a bunch for the help!

 

@MAX2 Wow, thank you for that comprehensive list! Do you think the head gasket is also bad? I would hate to spend the time cleaning the EGR system only to find out that the head gasket needs replacing and maybe something else got damaged inside the engine.
Is there a way that I can momentarily bypass the EGR system to let more air flow into the motor and see if that helps the misfires (that way I can know they are caused because something is wrong with the EGR system)?

@Mendel Leisk I was hoping you would chime in. Do you mind sharing with me what are the signs/symptoms that helped you know the head gasket needs replacing? Also, what would be the best way to confirm head gasket failure? Thank you!

@Tombukt2 thank you for the advice. I was thinking of replacing the motor with a generation 4 engine if the head gasket was the issue but now I'm not too sure. I have never done a head gasket but from the wonderful videos and instructions on this forum, it doesn't seem to be tremendously hard.

Thank you for the help!

Edit: Forgot to mentioned that when I replaced the struts I also replaced all spark plugs with brand new ones from Amazon. The car ran fine for at least 3 weeks before the trip. If the new spark plugs were bad, the misfires would have happen right away, correct? Just ruling out any other variables.

 

@Tombukt2 wouldn't bad/fake plugs cause problems right away? I drove it almost a month without any issues.

@Mendel Leisk thank you for the thorough explanation! As much as I would love my car to be the statistical outlier something tells me it is exactly like you say: clogged EGR led to head gasket failure.

@rjparker thanks for the help! I was hoping it was just a bad case of a clogged EGR system, if not, I would go the route of replacing the engine with a JDM generation 4th one. As much as I would like the challenge/learning experience, I'm not sure this car is worth the investment anymore

 

@Mendel Leisk forgot to mention that I'm not driving the car anymore. It shakes so bad that I just don't want to risk driving it (maybe if I press the gas enough it will stop shaking but it seems counterintuitive to me). If the head gasket failed in between cylinders (see picture below, taken from fellow member Pluggo's post in another HG thread), would I still see coolant on the cylinders that are misfiring? I just haven't noticed any lost coolant at all. If the head gasket failed between cylinders and coolant is not leaking into the cylinders, what is another good tell that the gasket has failed (besides the misfires and shaking lol)? Thanks again!

Prius Head Gasket Failure by ALTEREG0 posted Aug 20, 2024 at 9:08 PM

 

Thank you @Mendel Leisk! I will try swapping spark plugs, check engine codes, then swap coils, check engine coils. After that I will do the EGR blockage test (as shown in the first video @rjparker shared) and then I'll see if I can find the equipment needed for leak-down and/or compression test. Will an Autel AP2500 measure cylinder/engine compression (long shot, but it doesn't hurt to ask)?

 

Hello @rjparker, since these tests often pass with a Gen 3 head gasket (please correct me if I'm wrong but what I understand is that the head gasket on a Gen 3 Prius can often be faulty and the leak-down and compression test won't show that it is), is there a different test you would recommend?

Is there a way to tell which Gen 3 JDM engine has the upgraded pistons and rings (2015 I believe)? Will the VIN number accurately reflect the year?

 

I dared to go outside this evening to perform the tests as advised (switch spark plugs, switch coils and block EGR). It was a “cool” 100 degree cloudy day perfect for working on the car.
The first thing I noticed was that cylinder 1 spark plug was very easy to unbolt. I couldn’t get my hands on a borescope yet so I took some pictures of the inside of the cylinder but they didn’t turn out any good at all.
Cylinder 2 was not as loose, cylinder 3 was almost as loose as cylinder 1 but it was completely damaged (second picture below, first picture is in order 1-4 from right to left). Cylinder 4 spark plug was about as tight as the cylinder 2 spark plug, not sure if the tightness or the lack there of has anything to do with the issue.

Bought new NGK iridium spark plugs from the local auto parts store and replaced them, torqued to 15 lbs/ft. Took it for a spin and the car is not shaking at all anymore. Reset the CEL and took the family for a drive a couple miles away to have dinner with our cousin, drove back home with no issues and no CEL.

My question now is, what do you recommend I do next?

Here is what I’m thinking:

* Cleaning the EGR and installing an oil catch container
* Checking the cylinders with a borescope for any signs of head gasket damage
* Doing a coolant gas check (for head gasket failure)

Any other recommendations?

Could loose or defective spark plugs cause the car to overheat?

What do you think of spark plug # 3?

Could loose/defective spark plugs explain code P0401 “Exhaust Gas Recirculation Flow Insufficient Detected”?
Or is it more likely that the insufficient EGR flow caused the spark plugs damage and overheating?

Thank you again for all your help!

 

Hello again @rjparker! I'm going to do the coolant gas check as soon as possible as well as check the cylinders with a borescope as soon as I can get my hands on one.
Given the spark plug update, do you think I still need to block the EGR? I don't think so, right? Just clean the whole EGR system as soon as possible?

Most of the engines I've been looking at are being sold online. I know there must be a place around that stocks JDM locally, I will follow your tips on how to distinguish a JDM from a US engine. Any tips on how to distinguish an engine with the updated pistons and rings?

Thank you again for all your help!

 

Terrible indeed!
Any guess on what might be the reason for such damage on the cylinder #3 spark plug?

Will definitely clean the EGR and install an oil catch container asap! Thank you for the good advise.