Not Your Typical EGR Problem, New Member

Okay, so I bought my first Prius, a 2010 Prius 2 with 140k, about two months ago. Two days later, the CEL came on. P0401.

The first thing I did was to remove the valve, cooler and pipe to manifold for cleaning. It was gummed up all right. So I took the intake manifold off as well. Cleaned everything. In order to prevent this from happening again, I installed my own homemade oil catch can.

A few days go by and here comes the P0401 again. Feeling like I missed something, I removed the valve, cooler, pipe and intake again. Sure enough, I had missed those tiny secondary ports in the intake. Cleaned it all very thoroughly again. I also cleaned the MAP (which was a little gummy but not terrible), the MAP sensor channel in the intake and throttle body.

The code stayed off for longer this time, but alas, returned. Okay, so I take it all apart a third time, this time removing the exhaust manifold in order to clean the tube to the egr circuit. Exhaust manifold and tube were sooty, but no restrictions. Cleaned anyway. Put it all back together, cleared the codes and the CEL still returned!

At this point, I am getting mega frustrated. Everything is clean so I suspect the EGR motor is maybe at fault. So I pulled just the motor, tested continuity, and everything was within the specified range considered acceptable according to AllData.

Wth??? Since my brother has the exact same car, I switched the EGR motors to verify that was the problem. I was elated when his car threw a P0401. I figured I could replace the EGR and be done with this nightmare. Needless to say, I've pulled the EGR circuit so many times I think I could do it in my sleep.

However, after switching the "faulty" motor back onto my car, my brother's CEL returned on a car that had no previous issues with its EGR. Then my light returned as well.

Well crap... We played around with positioning the rotor in different ways during reassembly, but both cars keep throwing this code. And both cars have a "permanent" code persisting even after clearing the code with a scanner. Just for giggles, I disconnected the 12v battery to clear the code. Code returned yet again.

I understand that the motor is a simple coil that, when energized, spins a rotor to open and close the EGR plunger. But what I don't understand is, even if the rotor is misaligned during reassembly, why it wouldn't correct itself. It actually seems to correct itself after driving a bit. Car runs like poop for a bit then levels out and runs like the day it was made again. EXCEPT....P0401.

The plunger and rotor on both cars have been lubricated, the plunger glides smoothly during manual operation. So why is this code returning???

I am aware of the TSB and the warranty extension, but unfortunately, my car is not eligible with its mileage and because it's not registered in California. But honestly, my curious brain really wants to understand what's going on here. All components of the EGR circuit are clean and the EGR motor tests fine for proper continuity. This should not be happening! And my brother's 2010 Prius 3 which had no issues until I touched it, is doing the same thing now. This leads me to wonder if there isn't some alignment issue with the rotor and the coil after reassembly. But that doesn't quite make sense to me. Besides, I've tried it a few different ways.

Can anyone shed some light on this for me? Am I not properly understanding the way this EGR motor works with the plunger? I'm at my wit's end with this. Not quite sure where to go from here. I've scoured the internet and searched this forum to no avail. So I was hoping all you nice folks might be able to help. If my poor husband has to listen to me think aloud about this any longer, he might just kill me, lol.

 

I used throttle body cleaner to clean everything (and wiped the map down with a dry clean cloth). It took many, many, many cans of it.

I have not explored that avenue yet as I do not have a factory service manual yet. Any suggestions on the best place to get one at a reasonable cost?

The gaskets are definitely all on there. I dropped the rearmost one a few times trying to get the cooler back in. I was very careful to make sure they didn't disappear on me.

I am not seeing anything that appears to be wearing at all, besides gaskets and the skin on my knuckles. I make sure to take my time and do things the right way because I do still adore this car.

I have not done anything more than a visual inspection of the harness yet. But logic would lead me to believe the wiring is not likely the issue since the other car set the code when I swapped the motor. That, of course, may be my downfall. Very creative thinking on cross contamination though! I like that. (I did clean my connector, but not the connectors on the other car.)

Thanks for the replies, everyone! I'm trying to keep thinking of this as a fun little mystery, lol. But my deep well of patience for cars is wearing a little thin. I just find it really interesting and indicative of some issue with the removal of the motor/rotor assembly, seeing as how my brother's car was fine before I touched it. (I need to solve this issue not only for myself now, but for him.) I just can't for the life of me figure out what it is. I'm keeping my mind open and exploring all the options though. We all know how common egr problems are on these cars. It would be one unbelievable coincidence, but not an impossible one.

Anyway, when this is all said and done, I will have learned something. And there is some value in that. But in the meantime, I might lose my mind, ha ha!

 

I oversimplified, lol. I knew it was a stepper motor, but I didn't know the number of coils. I did read in another thread about the 111 positions though. I'm working on finding TechStream so I can play around with those positions a bit.

The only thing I touched on my brother's car was the motor, so I'm concluding that the position of the rotor during installation is the factor. I just haven't been able to pin it down. I assumed, since the egr is usually closed during idle on non hybrids, that this would be the case here. So that was the position I started with. I also tried it with the rotor halfway up the plunger shaft and at the top. No luck yet.

Just out of pure (and friendly) curiosity, what do you mean by that?

I feel like I have been reading threads and posts until my eyes bleed, lol. I will revisit that one on your suggestion in case I missed something.

And yes, you got it down. Can I hire you to translate my long-winded posts into something more to the point?

I assure you, the gaskets are in correctly. I know they are tricky, even for a seasoned mechanic, because they slid out on me a few times. I paid very close attention to them.

The metal has yellowed a bit from use, but restriction-wise, yes it does. I'm sorry I don't have any pics. I didn't take any but I will if I end up taking it apart again.

On the intake, I did use Berryman's and long round brushes to remove the buildup, then the throttle cleaner to rinse it all out.

I gave my brain a break on this today and will start fresh tomorrow. Regardless of the frustration, I am enjoying chatting with you all and I really appreciate all the advice and suggestions!

 

I didn't think it was derogatory. I just didn't make the connection. Lol.

I did use MAP sensor cleaner on the MAP, and TB on the rest. I apologize for omitting that information.

The interesting thing to me about both of these cars, is after the code is cleared and the light is off (but with a "permanent" p0401), the egr monitor completes and the light stays off after a few drive cycles. But then returns later. That didn't make sense to me until you mentioned the required driving pattern. Unfortunately he is in Colorado and I'm back in Indiana now. But I will send him the instructions and see what happens. At this point, I'd be happy to pay for a new egr if it would solve this problem.

A+ information! Thank you so much! I have new weapons to go to battle with, lol. I'm going to work on it today and I'll report back with any news.