2012 Prius - The Good Ol' P0301 Gremlin!!!

STATS:

• 147k miles (I am the original owner)
• Chevron gas only
  
• Sparks changed less than 10k miles ago
  • Coils not changed
• Everything else is original:
  • PCV
  • EGR
  • etc.
• No oil catch can
• Have yet to change transmission fluid

Last night, CEL lit solid for the first time ever with this car. Code scan reads P0301 (misfire on cylinder 1). First thought was "ohhhhh sh*t" as I have to travel 700 miles this weekend. Good thing the light flicked on just yesterday, otherwise I would have been stuck on some desolate road on my way to Los Angeles.

Interesting thing is the car did not knock at all when the CEL came on initially. This morning when I started the car, the CEL came on and I could feel/hear the knocking. Tapped the gas pedal and the knocking went away along with the CEL. Hence why P0301 is a "Gremlin"; only makes itself known when someone isn't looking for them (Volkswagon owners know Gremlins very well). As of now, there are between 5-10 city miles on the car since the CEL initially came on. I don not plan on driving it again till I can work on it. Renting a car for the trip to LA.

I have an engine compression test kit and and engine block tester ready to go. But as I have to travel this week, won't be able to work on this until next week. I am prepared to go all the way with changing out the head gasket (DIY) if I have to. But will start with the EGR cleaning, PCV valve change, maybe change the coil packs. I bought this parts planning on a tune up a while back, but never got to doing it. I am not a mechanic, but I have the tools and being a Ford owner of a truck, am conditioned for auto repair.

Keep everyone posted.

 

Alright, so what may make the CEL turn on, not initially exhibit symptoms of engine shaking, exhibit symptom engine shaking later on, then the CEL go off, and the shaking go away? The only thing I can suspect is the coil is bad. My car has never overheated. Never had issues with it. I've changed the fluids regularly. So tomorrow, I am going to check for just that to start. Then move to the compression and leak down test. Here is to hoping it is a faulty ignition coil.

I've been slowly building up my toolbox over the years; checking over at Slickdeals as I go along. There is a Harbor Freight nearby. I have Ridgid impact pools which I love (can't beat the lifetime warranty). I have Tekton sockets. I have an electric ratchet. I've made trades with a local guy that netted me 2 different Fluke DMM's. Should be able to make quick work of these two checks. Regardless of how this turns out, I am going to clean out the EGR and replace the PCV, perhaps even install a oil catch can. At worst, this is a blown head gasket and given my tool box is fully built out, I feel I can do that job DIY. Tomorrow's the day, wish me luck!

 

Thanks all. Just taking it step by step with the easiest things to do first. Though the wiper assembly needing to come off to get to the sparks to do the compression test is a chore, this is an easy job with the proper power tools or even hand tools. It sucks that you have to do this just to get the sparks. But if you've ever worked on a Ford engine (like this poor Ford truck owner), you know it is a piece of cake in comparison.

So I did the compression test and all cylinders registered at 119-120 PSI. That is good news; head gasket is still intact. Looking at the ignition coil on cylinder 1, I see no obvious damage. Will ohm it out in the morning with the DMM (digital multi meter). Looking at the sparks, spark in cylinder 1 has much more carbon build up on it than the others, so is definitely running lean. After the ignition coil test, will move to cleaning the MAF and changing the air filter, no idea when I did that last but it looks quite dirty.

And yeah, when the PCV comes off of course the intake manifold will come off and get a good cleaning and new gaskets at that time.

 

After removing the throttle body, I found the intake manifold to be full of oil/sludge right behind the throttle body. Gave the throttle body a good cleaning. Cleaned the intake manifold along with the 1/4" EGR ports found inside the intake manifold. Muck all over the place especially in those 1/4" EGR ports. Let it dry out in the 90+ degree summer heat before putting on a new intake gasket. Removed the EGR pipe and cleaned that too. I am thinking I might be short on time before the weekend, so I didn't tackle the EGR cooler or the injectors. I figure I can get to those later if there continues to be a problem. Plus, I want to isolate what could be causing the problem and if I did everything all at once, who knows what was the culprit.

While the intake manifold was drying, I installed a new PCV and an OCC (oil catch can). For the hose from the intake manifold to the OCC, I used a 3/8" x 3/4" barbed fitting to reduce from a very short (2-3 inch length) 3/4" hose to 3/8" hose (pretty much the same as how it is instructed in the NAB Youtube video. I actually don't like this reducer setup however. There is no pliability at where this is reduced down to the short distance from the manifold has to make before a bend has to be introduced. I am afraid over time this bend/strain will crack the plastic manifold. So I am going to replace that run of hose from the OCC to the intake manifold with 3/4" hose for that entire run. With the amount of sludge I saw in the intake manifold, I think it is mandatory for all Prius drivers to install an OCC. I also cleaned the manifold mating surfaces and the inlets.

Everything except the wiper assembly then went back in. I started the car and it was still shaking on a cold start. Bummer. I scanned the car again and now I have misfire codes on all cylinders. But then I forgot that during the tear down, I dropped one of manifold bolts into the engine bay. I had to jack up the car to remove the belly cover to retrieve it. After torquing it down, I cleared the DTC's and scanned it again. No more DTC's!!! But I know P0301 is gremlin, which means, it may turn itself up again when least desired. So I'll watch this over the next couple of days. Will drive the car sparingly and without the wiper assembly installed (just don't want to put it in yet if the gremlin decides to come back) as I pick up a few more things to finish off this repair.

A few things I noticed, my oil is low halfway though the 10k cycle. So I will do an oil change. I don't have any oil leaking or have I ever smelled oil burning. This scares me, so I'll see tomorrow how much oil really is in there. The car seems to be idling rough after starting in maintenance mode. I did clean the MAF and IAC and replaced the air filter while I was at it too. Still seems rough though. My coolant was a little on the low side, but nothing too crazy. And to be honest, i don't think I've topped it off since before the pandemic. I will completely drain and refill the coolant tomorrow too (I've only ever topped off my coolant thus far). Before continuing this, I'll start the car tomorrow morning cold and see if I get engine shaking; fingers crossed.

 

So I drove ~300 miles this past weekend and the P0301 error code and CEL did not come back. The Gremlin has been vanquished! To recap, the special things done were:

• Clean intake manifold and replace manifold gasket
  • The important thing here was that I cleaned out the 1/4" EGR ports in the intake manifold (see this video for those EGR ports)
    
  • This not shown in Nutz About Boltz video
• Replace PCV Valve
• Installed OCC (Oil Catch Can)
  • This is optional but after seeing how much sludge was in the intake manifold, I think it behooves every Gen3 owner to install one

Normal maintenance stuff that I did along the way:

1. Replace air filter
2. Cleaned MAF
3. Cleaned IAC
4. Cleaned throttle body
5. Oil and oil filter change
6. Topped off coolant

Diagnosis:

• Scanned ODBII to diagnose P0301 code (misfire on cylinder 1)
• Ruled out sparks as they were changed less than 10k miles ago
• Ruled out ignition coil by using Fluke DMM and visual inspection
• Further ruled out ignition coil by swapping into another cylinder (misfire did not move to another cylinder)
  
• Ruled out head gasket failure with Harbor Freight compression tester which I already own

Conclusion:

• Though PCV was changed out for good automotive hygiene, unlikely the PCV was the cause of a P0301 misfire code as that is isolated to one cylinder. A faulty PCV more likely would have produced a random misfire code. Highly likely the misfire being isolated to cylinder 1 was indicative of the intake manifold and EGR inlets being clogged as that was solved for with a good cleaning. Particularly at cylinder 1 where I noticed there was a large amount of sludge in the EGR port on cylinder 1, plus it is the port that is furthest away from the EGR and is likely to get clogged easiest (methinks?).

Maintenance yet to do:

• Reinstall wiper assembly (I made it 300 miles from San Francisco Bay Area to Lake Tahoe and back without issue)
  • Will do that this week
• Clean EGR valve and cooler
  • Will also wait for outdoor temps to drop before I do this as this is a mildly complicated job due to accessibility of fasteners and I don't want to burn in the sun working on my Prius
• Flush and replace coolant (only topped off for now)
  • Will also wait for cooler temps to do this in one shot with the EGR cooler cleaning as draining the coolant should make the previous process easier anyway
• Replace 3/8"->3/4" hose reducer for 3/4" hose along the entire run from intake manifold to newly installed OCC
  • I followed Nutz About Boltz instructions to do this. I just don't like the strain that this installation puts on the plastic intake manifold. I feel it could lead to breakage of the intake manifold. Will do that this week.

That's all folks. Thanks for the support and knowledge!

 

Oops, meant cleaned MAP sensor.

 

The compression tool I have. $30 from Harbor Freight tool and of course a wise investment. The leakdown test tool I don't have but might pick that up as I have a Ford truck with a blown HG to fix too.

But all good, all fixed now boss.

I feel that will still leave a short run that would not be pliable and might end up with the same situation where a bend and strain is introduced near the plastic intake manifold inlet, leading to the same potential/perceived problem. I feel it is better to use a 3/4" hose for the entire run to the OCC.

I'll take a snap of what I am talking about when I do this to illustrate what I am talking about, likely tomorrow.

Yeap, did this. Ignition coil is good.

It is all fixed now minus some other activities that need to be performed. Will wait for cooler outdoor temps to do those other activities mentioned above. However, 100+ degree heat of the summer right now is no bueno.

First time doing repair on my Prius. Thus far through 10 years and 147K miles it has only been maintenance. I would say that is damn good in terms of reliability.

 

Sparks were changed less than 10k miles ago, just before the pandemic. Probably only have 4k miles on them. I checked the sparks anyway and they were good; was the first diagnostic I did.

 

So the CEL has come back on twice since my first fix. After my first fix, I was able to travel from SF Bay Area to Lake Tahoe and back, then some daily driving for a month without issue.

The 2nd time the CEL came back on was 5 days before I had to drive from SF Bay Area to Los Angeles (same P301 code). I removed the intake again and was surprised to see it was quite clogged. I cleaned the intake manifold and re-assembled. CEL went away. I made it all the way to LA without issue.

As I was returning from LA, CEL came on for the 3rd time. Being that I was on the road in the wee hours of the morning and 100's of miles from home, I kept driving. This time I am getting P300, P301, P302. Coolant levels have not changed. Engine shakes quite a bit now at start up. A tap of the gas pedal right after start up calms it down, but does not allow for it to go away completely (as before). I suspect the EGR valve is the culprit and is stuck open. Ordered the kit and will replace it when it arrives. Will clean EGR cooler with pressure sprayer while I am at it.

Also, I noticed today as I was removing the EGR cooler, even with the hoses clamped off, there was a ton of coolant that spilled out of the EGR cooler. I don't know how the guys on YT do it where there is so little coolant that spills out. But I should have drained the coolant before trying to remove the EGR cooler as I had earlier planned (have never drained/refilled coolant since owning the car, 147k miles now). I skipped this, now have coolant all over my engine bay. I am going to have to do a good cleaning of the coolant to ensure no residue is left behind. Because if I do end up selling the car and there is dried coolant evidence, buyers might balk. Hoping this car tides me over till the Cybertruck becomes available. Then I can sell Prius (daily driver) and my truck.

 

Interestingly enough, there is a Gasket Masters nearby (I actually live in Manteca where their main shop is located). I'll get this EGR repair/replace done this week and will take it over to them and see what they say.

 

So just to summarize where things are at:

1. 1st time CEL came on, no engine shake initially
   • After some further COVID light driving (no long commute to work), there was some light shaking
   • Tap of the gas pedal on start would eliminate the shake
   • Intake cleaning made CEL go away
   • Added OCC and replaced PCV too
     
   • Probably 800-1000 miles were driven, then.........
2. 2nd time CEL came on, intake was dismantled and cleaned again immediately
   • Intake was significantly clogged after those 800-1000 miles were added after first repair
   • Cell went away though
     
   • Was able to drive 350+ miles to Los Angeles, no issues
3. 3rd time CEL came on was during drive back from Los Angeles
   • Kept driving during trip back to LA, no noticeable issues during drive
   • Drove lightly around town (< 10 miles) before attempting latest repair with EGR, then engine shake worsened
     
   • Before attempting latest EGR repair/replace, engine shakes as violently as demonstrated in video

No loss of coolant observed at any point. Even if CEL and engine shake goes away after EGR repair/replace, will take it into Gasket Masters as they are probably 3-4 miles away from me. Will go as far as replacing engine if need be as I need this car to last 2-3 more years.

 

Finally got the EGR cooler and valve out. The EGR valve is stuck/gummed up pretty good. 99.9997% of the time, I've only put in Chevron gas. Only times I don't is on long road trips where you have to get what's available to you or risk being stranded . The valve seat was in a more closed position upon removing it. But when I removed the solenoid and pushed down on the valve piston, it just sticks open and doesn't spring back into place as shown in the photo. Definitely, "aye" cause of the misfire.

I am sure it is not fully closing with all the carbon build up. Also, since I don't know if cleaning off the carbon fixes the problem as the electrical component (solenoid might be kaput or on its last legs). I bought a new EGR valve kit for that reason and will install it as soon as the rain breaks and I get one more needed part which is another story in itself. So no matter if there are further repairs needed (possible head gasket failure), replacing the EGR was necessary anyway.



........................I have all the requisite tools, but getting to the bolt under the EGR cooler took me 2 hours of trial and error! While I work slow, I am not clueless when it comes to car repair. I finally got lucky and got the damn bolt off. Because of that pain, I made the decision to leave the mounting stud under the EGR cooler in place. That of course then requires the two studs in the back of the EGR cooler to come off. Because of that, I I ended up dropping the EGR gasket into the engine bay as a result of this decision. Now I have to wait for a new part to arrive to get going again, LoLoL! Also, looking at the carbon build up in the EGR cooler, there wasn't any blockages as far as I can tell. I don't know if it was worth the trouble to completely remove the EGR cooler. Oh well. I cleaned it anyway with a pressure sprayer and brake clean.

When I do get this back together and if the knock isn't there, I will do a compression test just to see for myself if I am getting any compression loss. When the CEL came on originally, I did a compression test and things checked out then (some 800-1000 miles ago). I'll probably still take it into Gasket Masters and let them do a leakdown test and compression test or what ever other tests they have to ensure I don't have any catastrophic engine failure.