P0401 code - mechanic changed EGR - but still showing code - suspect catalytic converter (??)

That sounds like head gasket failing, allowing coolant to leak into cylinder. There's no misfire code, p030X (with X being 1 through 4, representing cylinder number)?

Did your mechanic ever clean the intake manifold? It has crucial EGR passages, feeding the exhaust gasses to the engine intake ports. And yeah, it'd be good to see just how well they cleaned or replaced the other EGR components.

There's a school-of-thought, and I subscribe to it, that the EGR clogging is what causes head gasket failures.

 

There are 4 key components in the EGR circuit: the intake manifold (not pictured), the EGR pipe (green), EGR valve assembly (blue), and EGR cooler (red). Each of these may get clogged over time, but can usually be cleaned out with a little effort without having to resort to replacement. Did your shop replace one or all of these components? Were the replacements cleaned out before they were installed? A blockage in any of the 4 components means there is effectively a blockage in the entire circuit—all of them need to be clean before installation.

P0401 is set when the ECM opens and closes the EGR valve (for a test) during regular driving but sees a pressure change of less than 1 kPa. In order of decreasing likelihood, this can happen if:
1. any of the 4 components above are clogged,
2. the manifold absolute pressure sensor is malfunctioning, or
3. the ECM is malfunctioning.

The catalytic converter has nothing to do with this. As Mendel pointed out, if they replaced the entire EGR assembly (pipe+valve+cooler) but did not clean the EGR passages in the intake manifold, you would still end up with P0401.

 

Maybe. If the intake manifold EGR passage at cylinder one is near-totally carbon-clogged, BUT two through four are still flowing more, you might dodge the code, but still have one cylinder starved of exhaust gas. And the car’s computers none the wiser.

 

No. The car's judgment of P0401 is made solely by opening the EGR valve and observing the effect on intake manifold pressure. If the pressure increase is too low, the EGR passages are judged to be clogged. The catalytic converter is not involved.

 

I will offer at least one bit of advice. Unplug the egr valve electrical connector and allow the car to run in a non egr map until you get the egr system cleaned. The entire egr system needs a cleaning as its all clogged in varying amounts so that may eat you on labor cost and you may not think its worth it to mess with. But running the car with the system clogged like that is 100% testing the head gasket. You will get a failure if you keep the p0401 and keep going. For me a p0403 was better than a p0401 as the knock sensor threshold on these cars is too high and it really is bad for them (running the p0401 gives you a lot of knock, the p0403 gives you no knock). Maybe the unplugging of the egr valve electrical connector will stretch your dollar a bit further if you decide to run the car until it dies if you decide its not worth it to repair. I imagine the whole egr cleaning will be very expensive.

 

As long as the check-engine light is on with either a P0401 or P0403 code, you are already running with the fail-safe (non-EGR) parameters. The fail-safe chart specifies the same behavior for both codes.

Just don't go unnecessarily clearing the code. Then you'd be running without the fail-safe protections, for as long as it takes the car to re-run the P0401 monitor and set the code again.

 

I would have to see that. i did forget i never actually got a p0401. p0403 runs great though. i would like to say clean it and run it or don't run it until you clean it.
he says he has a p0401 and it runs like shit above so he better try unplugging it and saying a prayer to whatever god he believes in

 

But the mechanic has probably cleared codes with every "thereifixedit" attempt, so the car keeps not knowing it has a flow problem, until it runs the test again and finds out and redisplays the code.

 

wow! OP use your butt sensor. if you think the motor feels wrong, verify by unplugging the valve.

 

If P0401 is already set and the MIL is on, unplugging will additionally set P0403. I'm not sure how this would help.

 

Just so you get no chance of getting any EGR valve opening and I have seen the p0403 map runs fine. They could be the same though, but i wouldn't want to chance getting any egr at all until its cleaned.

 

it's definitely not the map sensor or the egr valve. But cleaning the valve is helpful and easy. p0401 means they did a shit job cleaning it. You will need to take it all apart again and clean and verify it's all clean again. Clean the EGR cooler until you can see through it. Don't play the games though. Games with the various levels of egr clogging only result in head gasket failure. I would imagine labor and kit is $2000 for that.

 

The exhaust gases enter the intake manifold through the port circled in blue, pass through the EGR gallery, which finally splits into four exit passages circled in red. When you pull the manifold off a high-mileage Prius you will usually find this entire circuit filled with carbon deposits. That is more important to clean (than the oil under the throttle body) if you're looking to clear up a P0401.

Troubleshooting is a linear process—you point a finger at a possible trouble area, check whether it is functioning properly independently, and if it is, you move on the the next suspect. If you find a malfunctioning area, you fix it, check if the code went away, and your troubleshooting ends there. The suspects are usually lined up in order of increasing complexity, or in increasing order of the number of other systems they interact with. The very last trouble area is, therefore, usually the ECM (which is both highly complex and interacts with a lot of systems), and if you're left pointing a finger at it, you have to replace it. It is highly unlikely your ECM is bad.

 

The MAP sensor is what the car uses to confirm the EGR flow and decide when to say P0401. So it's not like checking the MAP sensor was an out-of-left-field idea. But there might be easier ways to check it than taking it out. If you just look at the MAP reading in Techstream, and it's around atmospheric pressure (14.7 psi or so) when the engine is off, and lower near 4 psi when idling, you'd pretty much say "MAP sensor's ok" and not bother taking it off and molesting it.

An EGR valve with a mashed ski jump definitely can give you a persistent P0401. Look no further than the name of the thread where we first learned about mashed ski jumps:

Still P0401 after cleaning egr !! should we drive it? | Page 3 | PriusChat

The ski jump is a little stop you can see if you completely unscrew that rotor you find in there, and look up in the center of it:



Compare one that has had a track mashed right through it:



ozmatt managed to fix it by using a heated butter knife to smrsh the plastic back into shape, but that's pretty hardcore. It's easier to put in a new valve.

 

In the video he's using a 10-32 x 3/4 machine screw. An imperial measure screw. I'd be real cautious with that. I'd suspect they're M5 screws, have purchased a few in advance, socket-head cap screw style.

There's a couple of EGR valve part no's on this page:

https://www.amayama.com/en/catalogs/toyota/prius/3-hatchback-right-xw30-2011-r-2828/engine-fuel-system-and-tools-1/exhaust-gas-recirculation-system-52

25620-37110
25620-37120

There was a rev to the valve, guessing the second one is the rev'd version? It's the part number on the box in the video, fwiw.

Anyway, just food for thought. See what the price is with shipping for you. When I view the page in Canada, for the second one (...37120) I see:


So far for me, having made 4~5 purchases through them, item cost plus shipping is "all in", no extra charges, say taxes or duty.

 

I just looked at that video. I noticed there was one misinformed commenter who made two comments on it, "That part you're calling a stepper motor is a solenoid coil" and "The magnet just threads on. Spinning is not part of its operation", both of which are the opposite of true. It is indeed a stepper motor, and spinning the rotor is indeed what opens and closes the valve.

If I had a youtube account, I would add a comment there correcting that. Maybe somebody else can?