Techstream EGR Valve Blockage Data

Hi! I have a '09 Prius III (~180k miles), cleaned the whole EGR system approx 1,5 year before.
The car did run fine since the last two 3 months.
After that i got rough idle/cruising and P0401. Cleared DTC then. There isn't any DTC since then, however ICE runs roughly sometimes (when cruising with constant RPM -typical "EGR valve is opened" usage-, or when car is idling).
I have Techstream data when i got P0401:


Maybe EGR couldn't close enough how it should be in my case? Because my test result was exactly 0.00, as shown the picture.
MAP sensor was dirty as hell, cleaned it with proper chemicals (without any phisical contact ofc), but it didn't help.
So car is running, no DTC, but sometimes make rough idle (not on cold start!), and on mild cruising.
Did EGR step position test too, ICE starts to rough idling around 11-15 steps, however when i decrease it to 0, then it not really makes any sense to make idling smooth again. What do you think? Maybe there is still some debris on the EGR valve stem itself, cause stucked valve?

 

Presumably when you say it’s a 2009 it still is a 3rd gen Prius? Your location being Hungary, the convention is to identify by build-date? I have a North American “2010”, as described by Toyota here (Canada), although its build-date was August 2009. Info

Did you clean the EGR passages in the intake manifold?

what’s the miles?

the EGR valve may have internal damage, isn’t performing properly. @ChapmanF may chime in with more info.

 

You cleaned the map sensor, not the maf sensor?

Probably an egr air leak or a sticking egr valve. Try a block flow test. There is a revised egr valve available for a first year gen3.

no cost egr block flow test

 

If you're getting a very low flow number, or a P0401 code, doesn't hurt to check the valve for a rutted ski-jump, which can contribute to that.

 

Hi Mendel,
Thank you for your reply. Yes, it's a 3rd gen for sure, produced in 2009 via Toyodiy according to VIN number. 2nd gen doesn't have EGR at all, IIRC
It's a very early 3rd gen, zenki model of course.
~180k miles in her.
Sure, i've cleaned the intake passages, EGR cooler, everything.
Sorry for my bad english.

 

Thank you! Yeah, i've cleaned the MAP, located next to the throttle body, over the little oil swimming pool
I've already bought a revised one EGR, but before i replace it i'd like to make an exact diagnosis as well. We have 3 HSD in our family, so this revised EGR valve could be useful later too

 

Hi Chapman,
Thanks. Yes i know the "ski-jump" thing, i've checked it. It's been in quite in good condition, like an unmolested "ski-jump".

Hi ChapmanF,
Thank you, I've checked the "ski-jump" already. Seemed absolute fine and mint

 

Presumably then the car’s first EGR cleaning happened around 150~160k miles? That’s quite late; I’d be on alert for head gasket failure signs: dropping coolant level in reservoir, engine shaking during cold-starts.

 

@RWD Any initial test is to physically block the EGR passage and analyze effects.

The professional TCCN video linked by @rjparker shows this.

Also - as you have techstream - you can force close this valve via the EGR active test with engine running….

Step 0 is closed valve.

If the EGR valve is clogged, physical block analysis - compared to the effects of step zero - with reveal this issue.

 

Production of the 3rd generation began mid-way through the 2009 model year, as car model years are conventionally defined as beginning circa October. Just to confuse everybody, Toyota designated the early ones as 2010s in the US, but 2009s elsewhere. Once upon a time (see orignal Ford Mustang, for example) mid-year introductions were unofficially designated something like "2009½," as it would've been in this case.

 

For anyone about to use that EGR step active test, it's good to take a look in the repair manual for some things Toyota wants you to be careful about, some collected in this post in 2019.

Generally, when you'd be doing such a test, the engine will be idling; its target EGR step at idle is zero anyway. In the places where the repair manual suggests using the active test, it is generally having you override the normal zero target with a higher step, to see what happens then (and then leave it the way you found it by setting back to zero).

Any time the target step is zero already, setting it to zero with the active test doesn't do anything more to force the valve closed ... if the ECM targeting step zero hasn't closed it already, it's not like you get a more forceful step zero by requesting it in the test.