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

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by ALTEREG0, Aug 19, 2024 at 6:50 PM.

  1. ALTEREG0

    ALTEREG0 New Member

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    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!
     
  2. MAX2

    MAX2 Junior Member

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    P0401 Exhaust Gas Recirculation Flow Insufficient Detected
    P0300, P0301, P0303 -
    P0300 Random / Multiple Cylinder Misfire Detected
    P0301 Cylinder 1 Misfire Detected
    P0303 Cylinder 3 Misfire Detected

    Trouble Area:
    • Open or short in engine wire harness

    • Connector connection

    • Vacuum hose connections

    • Ignition system

    • Fuel injector assembly

    • Fuel pressure

    • Mass air flow meter sub-assembly

    • Engine coolant temperature sensor

    • Compression pressure

    • Valve timing

    • PCV valve and hose

    • PCV hose connections

    • Intake system

    • EGR valve assembly

    • ECM
    There are many problem areas, but you need to start with cleaning EGR

     
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Replace head gasket. Clean the EGR components, including the intake manifold too. Reclean every 50k miles thereafter.
     
  4. Tombukt2

    Tombukt2 Senior Member

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    This is when you should be putting this model to rest forever unless yours is an exceptional condition like really nice condition I mean really nice which I don't know even how that's possible but anyway that would be subjective this is when you do nothing You can have $8,000 in this nonsense very quickly and still have no car and the car realistically is barely worth six or a lot less I'm sorry it's a 2010 so you don't do things like that generally making good sense If it's Prius you must have just because of whatever you can buy a generation two for $700 to $3,000 wherever you stand in the pool of people to buy I stay in the 700 to $1,000 range have four of them a generation 3 can't hold the candle to any of these four cars or any generation 2 as far as I'm concerned I've got two generation 3 sitting out here getting ready to go to pasture because they are not the one that's right and that's the end of that You only get a chance basically to get me once with that nonsense.
     
  5. ALTEREG0

    ALTEREG0 New Member

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    @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 likes this.
  6. Tombukt2

    Tombukt2 Senior Member

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    Now we're going places It all comes out in the wash You may have fake spark plugs from Amazon and they are askew. You need to go to the dealer or you can even go to advance Auto in Menards and buy like NGKs or even auto lights just to test and see I get auto light iridium blah blah blah whatever they are they got they look like NGKs almost but they're not and I use those to test with and then if everything clears up and runs right then you can either run to the dealer or find an authorized nippon denso distributor through the site in the US I mean irregardless these things should be like $44 a set from an authorized seller then decent sets you know the SK16s it's a bread and butter plug for them so anyway see if that's if that's straightens you out You may just have really shitty plugs you need to address that quickly because if they fall apart inside the motor if they haven't already well there's your problem and I feel for you because you may need a motor crap.
     
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    First the statistics:
    1. 188k miles (Gen 3’s with untouched EGR reliably blow head gaskets, by those miles, or even less. They’ve let go as early as 120k.)
    2. P0401 (Code for insufficient EGR flow)
    4. P03XX (Misfire codes, typically due to head gasket failure, typically starting with cylinder 1.)

    My 2 cents: long-clogged EGR caused head gasket failure. Cleaning the EGR, while needed, should be second priority. A cleaned EGR system won’t “heal” the head gasket. You need to deal with the head gasket first, and then the EGR cleaning, to avoid another head gasket failure.

    For DIY the easiest diagnostic is likely a boroscope inspection. First thing in morning after driving the day before would be optimum. Look for pooling coolant atop piston, exceptionally clean piston, and coolant tears running down cylinder wall from head gasket seam.

    video #13 here:

    Nutz About Bolts Prius Maintenance Videos | PriusChat

    will help with spark plug removal. Contrary to the video, best to torque plugs to 15 lb/ft, with clean threads.

    when the EGR system gets carbon buildup:

    1. the EGR cooler’s internal radiator, coated with carbon, both loses its cooling ability, and reduces overall exhaust gas flow.
    2. The EGR valve and pipe (between valve and intake manifold), also carbon coated, further reduce exhaust gas flow.
    3. The intake manifold’s EGR passages also clog up with carbon, and tend to do it in sequence, commencing with cylinder one.
    4. Now you have an engine, which relies on EGR flow to modulate combustion, with reduced and overheated exhaust gas, with cylinder one nearly starved, while the remaining cylinders still have partial flow.
     
    #7 Mendel Leisk, Aug 20, 2024 at 6:23 PM
    Last edited: Aug 20, 2024 at 6:47 PM
  8. rjparker

    rjparker Tu Humilde Sirviente

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    An egr allows exhaust gas into the intake at normal driving speeds, not air, Actually you may want to block the egr to test if it reduces your symptoms. Normally an egr that is not closed at low rpms will cause stumbling and stalling, not misfires.

    Car care Nut Egr video with block tube test
    If the car is burning oil badly, the egr system will get clogged. At that point a rebuilt engine with revised pistons and rings is suggested.


    Car Care Nut HG Borescope at 10:57
     
    #8 rjparker, Aug 20, 2024 at 6:55 PM
    Last edited: Aug 20, 2024 at 7:13 PM
    Brian1954 likes this.
  9. ALTEREG0

    ALTEREG0 New Member

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    @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 :(
     
  10. ALTEREG0

    ALTEREG0 New Member

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    @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!

     
    #10 ALTEREG0, Aug 21, 2024 at 12:09 AM
    Last edited: Aug 21, 2024 at 12:17 AM
  11. Mendel Leisk

    Mendel Leisk Senior Member

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    Another thing you can do, on the way to boroscope inspection:

    Your misfire codes indicate cylinders one and three. Swap the plugs first, between those cylinders and cylinders two and four. Then check if the codes change. If not, then swap the coils similarly. If the codes still do not change, it's more likely head gasket failure, at one and three.

    Then let it sit overnight, and do the boroscope inspection.

    Just leave the wipers and cowl off for the duration. It's a pain, but the only way to get the plugs out.
     
  12. Mendel Leisk

    Mendel Leisk Senior Member

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    Leak-down test is also good; it's the traditional go-to I think. Compression test as well. Both of those are trickier. Leak-down requires compressed air, and should be done with a special gauge set.

    Talk to a dealership service department, tell them the symptoms, see what they'd charge for a diagnostic?

    The "usual" is coolant leak thus:

    upload_2024-8-21_11-40-2.png

    Then as it becomes more advanced, other cylinders succumb too.
     
  13. ALTEREG0

    ALTEREG0 New Member

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    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)?
     
  14. rjparker

    rjparker Tu Humilde Sirviente

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    Pressing the gas hard enough to stop it is a very good test indicating hg. If it won’t stop your back to plugs, coils or injectors. However the hg problem is widespread on gen3s with age and high miles.

    These tests often pass with a gen3 hg.

    It is possible you have a cylinder to cylinder leak but that is rare.
    If you are not going rebuilt I would stay with a gen3 JDM that you handpick. Gen4s require many parts off the gen3 engine like the intake, exhaust, egr and have different hose routing along with harness cables that need extending.

    If you go JDM look for excessive corrosion and physically broken parts. Turn the engine over by hand with the plugs in. Look for X2ZR-W20 on the JDM engine instead of the US engine’s X2ZR-W25. The injectors should be tan rather than blue. Otherwise you are likely to get a high mile US engine sold as a JDM. My local hybrid shop has good luck with the handpicked JDMs but he has only three or fours years using them along with more expensive rebuilts.
     
  15. ALTEREG0

    ALTEREG0 New Member

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    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?
     
    #15 ALTEREG0, Aug 21, 2024 at 6:17 PM
    Last edited: Aug 21, 2024 at 6:28 PM