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

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

 

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

 

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.

 

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.

 

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.

 

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