Techstream EGR Valve Blockage Data

If the "min" is measured at closed EGR valve, it should be "no EGR flow" at all...

And 0 kPa is pure vacuum...

The atmospheric pressure is about 1013 hPa, 101 300 Pa.

The "min" is about 1 kPa, 1000 Pa, so it is the vacuum in the IM, if the engine is turning with no injection at all (it is 0,01 of the atmospheric pressure - no idea, if this _can_ be the absolute pressure in an IM of a ICE ).

Mat

 

It isn't. It is the threshold at which a test value indicates a problem. This is per OBD-II standard, not even something specific to this test.

The reported "test value" is a difference between two pressure readings, not a single pressure reading. During a fuel-cut deceleration, the ECM takes a manifold pressure reading, then opens the EGR valve a certain amount, then takes another manifold pressure reading, and subtracts. The difference is the reported test value. If there is no EGR flow, then opening the valve has no effect on the pressure reading, and the test value will show a difference of 0 kPa.

It can't. At normal idle, EGR closed, the MAP tends to be around 27 or 28 kPa. Under fuel-cut decel conditions, that can be pulled down closer to 15 kPa.

If the ECM then opens the EGR valve and sees the reading rise to 36 kPa, that would be reported as a 21 kPa test value, roughly what we see for a freshly-cleaned system.

If opening the valve only raised the reading to 25 kPa, that would be a 10 kPa test value, roughly what I had before cleaning at 15x,000 miles.

If opening the valve only raised the reading to 16 kPa, that would be a 1 kPa test value, and be close to lighting the CEL with a P0401 code.

If opening the valve left the reading unchanged at 15 kPa, that would be a 0 kPa test value, and indicate no EGR flow whatsoever.

 

Wow!

That is an answer!

Thank you!

All is very clear now for me!

Mat

 

Thanks a good thread. I get very good new information.
Have you any idea, why misfires comes if EGR system is blocked? Because if EGR system is block, i think burned gas not flow to cylinder. I understand if couple IM small EGR port is block, then exhaust gas flow too much on other cylinder. But if all IM ports is open and my EGR test result is 16,07, misfires comes on little acceleration. TS shows couple misfire on cylinder 4 or cylinder 3. But no show any fault codes.

 

Love the discussion here. Learning quite a bit! Thanks guys!

 

The misfires are more likely due to failing head gasket, which in turn may be due to long-neglected EGR clogging.

 

"EGR test result is 16,07" does not sound very critical...

How many miles, how old is your car?

Cylinders 3 and 4 are the less clogged up at most cases.

I believe, I read in this thread a good reasoning from ChapmanF in regard to knocking/misfireing cylinders due to clogging...

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Found that here: How to prevent the 3rd Gen Prius Headgaskets failure! | Page 2 | PriusChat
He is speaking about knocking of the most clogged cylinders, and this would be the 1 and 2, so I would risk to say, the 3 and 4 would get too much EGR and could misfire (my reasoning - I am not a mechanic)
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Misfires can have many causes - one of which is the one pointed out by Mendel Leisk above.

Mat

 

Yes, I know that. But the coolant fluid is normal level, and never morning heard any knockin from the engine.

The car is Toyota Auris hybrid. modelyear 2010. And about 160000km. Hybrid system is same 3rd gen Prius.

 

If the EGR system is completely blocked, then any misfires you may experience are caused by something other than EGR.

There is one familiar pattern where misfires are caused by EGR. Because EGR is not used at idle, and is not used at high load, but is used at moderate loads, if you have misfires that only occur at moderate loads, but not at idle or high loads, they could be EGR-related. Typically, that will mean that the four passages in the intake manifold are clogged by different amounts, so that at moderate load, when the EGR is introduced, it leads to mixture imbalances between cylinders.

A test result of 16,07 means your EGR is far from blocked, overall.

 

Thanks ChapmanF. Misfire comes only moderate loads. I have another thread this misfire case. I write here because this is very interestig thread. I interest how the EGR system works and how I can diagnose it. I will continue in the other thread. Keeping this thread for the EGR diagnose.

 

Could you point to the other thread?

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Yesterday I read the EGR flow again and got the value of 20,64 (22-05-2022)
The value from 15-05-2022 was 19,94.
The "min" was unchanged - 0,97.

So this is the kind of difference, one can see in the values - somewhere about 0,6 kPa.

I will try to make some more tests and see what happens

Mat

 

Misfire and shaking but only when i turn | PriusChat

 

I think it can be larger than that. Before I cleaned mine, I was seeing 10 point something mostly, but I'm pretty sure I saw a 14 point something one time among those readings. I think there was somebody else earlier in this thread who, after cleaning, was getting the expected 20-ish numbers mostly, but an occasional 16 or 17 or something (I haven't scrolled back in the thread to find the details).

So, outliers that large seem to be rare (as respectable outliers should be), but occasionally seen. The price we pay, I guess, for a test that the ECM sneaks in during ordinary driving, without having full control of the conditions.

 

OK - good to know - I will keep my eye on it from time to time and eventually report here

Mat

 

I don't believe the catalyst oxygen storage test value is bad. My car is same value 0,224 / 0,226 / 0,220 / 0,221. This results are same testdrive.
Km is same about 160000km, and I know the original CAT works 400000km, if not lot of misfires or oil burned.

 

If only I had seen this before cleaning ...

Question: what does it take to complete the test? My 2011 does not have a completed $31:$bd test since I buttoned it up most of a week ago.

 

You can read over the "confirmation driving pattern" for P0401 in the repair manual. It roughly involves getting the engine warmed up in inspection mode, driving a certain distance within a certain speed range, then doing at least five seconds of foot-off-gas deceleration in B mode, which makes the ECM say "hey look, these are the conditions where I sneak that test in!"

 

Don't have a repair manual, but did find this in a thread: "A speed of 25 - 37 mph for more than five minutes, and then releasing the accelerator pedal for more than 5 seconds,"
Glad to find that, and find the raw OBD2 info: Mode $06, PID = ( MID: $31 // TID: $bd )

I'll go test it after I finish installing my new gaskets

 

Oops. One more CRUCIAL element: must drive in Certification mode (ie Traction HV motor off) so the engine doesn't stop! @Mendel Leisk shared a link to the official instructions: 2012 Prius DEATH RATTLE persists AFTER replacing EGR valve etc. | PriusChat

 

The mode you want is the one that keeps the engine running; that's the first option ("2WD for testing exhaust gas"). The second option ("for disabling TRC") is more for speedometer/dyno testing and the like.

Gen 1 and 2 had a single inspection mode that did both, but Gen 3 split that out into two modes.

There are warnings about driving much with TRC disabled; hard on the tranny if you're not careful.

If you use the chicken-dance method, the first mode is the one with two pedal stomps, and the second is the one with three. (Or should I say six versus nine?)