Techstream EGR Valve Blockage Data

@ChapmanF and @burebista how many miles do you have? Just wondering how long it takes.

 

Looks like I posted this result last 22 December. That was about 154,000, um, international customary miles.



So if I remember to pull it again this 22 December, that will be a year. If it has dropped to 0.250, say, I'll start saving pennies faster. If it still says 0.251, I'll figure maybe it changes too slowly to tell me much over a year's time. If it says, say, 0.252, I'll say there's too much test variation to infer a dropping rate over such a short time scale.

Looking at burebista's result, it looks like this might be another graded-on-a-curve test where the min value changes. That adds some extra murk.

It is another one of these tests the ECM sneaks in during normal driving. It will deliberately undershoot the proper fuel injection volume for some seconds, making a lean mixture with unreacted oxygen that gets stored in the cat, and then deliberately overshoot the injection volume and see how long it takes for the (downstream) O₂ sensor to show the oxygen level low, which only happens after the O₂ stored in the cat is used up, so the longer it takes, the better.

 

@Mendel Leisk 316k km (almost 200k miles)
@ChapmanF That minimum value doesn't change. It's carved in stone.
Always 0.2196 (I have a screenshot from July when I saw the lowest value for EGR monitor bank).

But that reading value changes almost daily. Usually is 0.22xxxx but I saw it once 0.220515 and once 0.24xxxx.

So if I understand it right, it's about catalytic converter and I can't do anything to save it's life.

 

In my screenshot it's 0.249, so nyeah.

 

Yeah, but you have an US Prius, mine is an EU Prius.

 

A thought about EGR cooler carbon blockage: beside air-flow reduction, it's been mentioned here, that carbon-coated radiator plates will be less effective at cooling. How much of a factor might that be?

 

I don't know. Have you thought of a way to look it up or find out?

 

I need to run this egr test. I have done only basic things with it like health and battery check. How do i navigate to this egr test?

 

What are you using for a scan tool?

 

I didn't pull it again in December, but I did just now and the catalyst oxygen storage test value is still 0.251. So it doesn't seem to drop very fast, anyway.

The EGR flow value is 22.89 kPa, nine months after cleaning.

 

How do you navigate to this test with techstream? I have it on old laptop that i used to program my tundra keys.

Just picked up my prius about a month ago and did egr/intake cleaning couple weeks ago, 2011 180k.

 

The screenshot pretty much says it. There's another in post #1 of this thread. From the "Engine and ECT" screen, you show the Monitors. There is one for Exhaust Gas Recirculation (the topic of this thread). There's a different one for Catalyst Efficiency (a bit OT for this thread, but did get mentioned now and then, including by me.)

 

As I promised to ChapmanF in another thread (How to prevent the 3rd Gen Prius Headgaskets failure! | Page 3 | PriusChat), here are values of two Priuses of the family (none of which has EGR ever cleaned):

My Prius:
Value: 19,94 kPa (tested on 15.05.2022)
Min: 0,97 kPa (I see the min value slightly different in other peoples results - has it any relevance?)
Max: 655,35 kPa

The car:
94 697 km (58 842 miles?) at 19.05.2022
Production year: 2009 (Europe, sold in France, imported to Poland with approximately 55 000 km)
Very short trips in average.
The average from the last 500 trips, almost 2 years of driving is about 9,5 km (I'm surprised myself, but I realised, that trips of about 200m from my flat to and from my garage are inside ).
Average consumption over this 500 trips: 4,4 l/100km (53,46 MPG) - not bad for this old car

The second one:
Value: 18,37 kPa (tested on 20.05.2022)
Min: 0,95 kPa (I see the min value slightly different in other peoples results - has it any relevance?)
Max: 655,35 kPa

The car:
92 348 km (57 382 miles?) at 19.05.2022
Production year: 2012/2013
Have not that mutch information about this car - is driven without HybridAssistant

Mat

 

I don't really know the explanation of the variable "min" value. One possibility is that, because this is a test that the ECM sneaks in during normal driving, the test conditions aren't always identical, and the ECM might have some formula for adjusting the "min" value as a way of grading on a curve.

But that's just one possible guess. I have sometimes wondered if we would see less test-to-test variation if we compared the ratio "reported test value ÷ reported min" rather than the reported test value alone.

 

It would be possible, that both values - "min" and "value" are measured quantities.
The "max" could be a value resulting from the memory capacity, this value can take. The 655,35 looks very similar to 65535 - a value, a 16 bit variable can take. If you take this and divide by 100, you get two significant digits after comma - 655,35 (in US it is a dot, right?).

If I understand it right, the "value" could be a difference between two states - EGR valve opened and EGR valve closed or simply the measured value at opened EGR valve.

The "min" could be the closed EGR valve value and the "value" could be the opened one (or the difference between the two). Did I doubled the same thing here??

I do not know, if it makes sense, if one looks at the kPa values - do not have enough knowledge

Mat

 

In my understanding, every mode 6 monitor test in the OBD-II world is a thing with a test value, and min and max thresholds where DTCs will be triggered if the test value goes outside them.

Certain tests are only bad in one direction, like this one, where clogging makes the test value go downward. When you see what you correctly spotted as the scaled, all-ones value for "max", that means "for this test we don't care about a max".

According to the manual, this test value represents the increase in manifold absolute pressure that results when the valve is opened a certain amount during a fuel-cut deceleration with the engine turning.

 

So, we actually know, what it is.

Power train state:
- Fuel cut off
- Engine turned from the other side, RPM unknown, maybe the measurement time point is defined to a certain RPM? (engine braking - here contributing to the deceleration without breaks, I think)
- Throttle - is the throttle here wide open? I would assume this.
- VVTI - plays a role too, I think

EGR valve closed: measured "min" value

EGR opened to a defined state: "value" measured (we do not know here how much the valve is opened, if it is not max opened?)

So the actual relevant value would be ("Value" - "min") - the difference.

Or should the "value" already be the difference between the two?

So many questions

Mat

 

I don't believe that interpretation of "min" can be correct.

As I understand it, the OBD-II standards dictate the structure of a mode-6 test. It will have a single reported test value. It also has a min and a max, which are properties of the test. A failing test is a test value that falls below min or above max.

If a particular test doesn't have a min that matters, or doesn't have a max that matters, the corresponding min or max will simply be reported as some value outside the test value's range.

So the min and/or max for a mode 6 test will involve an engineer's judgment of when the test value is bad enough to warrant setting a trouble code.

Some mode-6 tests have a min or max that's clearly a fixed value. This is not the only such test where the min value has been shown to be something that's computed. How they compute it isn't explained, but its purpose is still to indicate the threshold where a trouble code will be set.

 

Do you mean, that first when the "value" falls below the "min", there will be a trouble code generated?

This would mean "no EGR flow" at all...

Do we have people with a trouble code AND an EGR flow measurement in this state?

Mat

 

The "min" value typically seems to be reported around 1 kPa. That is about one twentieth of the test value in a squeaky-clean system, but it is definitely not "no EGR flow" at all, which would be 0 kPa.