Techstream EGR Valve Blockage Data

Have you been simply pulling up the monitor value once or twice a week? Or clearing it and forcing a new monitor cycle to run?

Have you cleared and forced another cycle to run since the 13.xx you saw recently?

Was there anything different about your driving leading up to that recent reading?

I think there are a lot of variables in the way the ECM generates those numbers. It tries to sneak a test in while you are decelerating in normal driving, so there can be a lot of variation in the conditions.

My before-cleaning numbers in #92 seem at first very consistent: 10.41 from last December, then 10.93 and 10.33 close together last week before I did the work. But what I didn't mention in that post was that I'm pretty sure I saw one or two 14s or 15s back in the late winter/early spring that I didn't write down.

So it seems to be possible to have some relative outlier readings from time to time. If you haven't cleared and rerun that monitor since the 13.xx, I think I would definitely try that once or twice, before being totally convinced that it really worsened by 25% on the way from 199,500 to 199,700 miles.

 

How to clear it?
I just monitor it in the morning before going to work. Start the car, wait one minute for engine to stop and then check that value.

Nothing changed in driving habits. Just city driving during week and one short road out the city (37 miles) in weekend to my brother-in-law.

 

Doing a DTC clear (even if there aren't any DTCs to clear) resets all of the ECM's monitors.

It will then re-do all of them at its earliest convenience whenever your normal driving happens to meet their preconditions. (The EVAP monitor is kind of an exception, it doesn't run while you're driving, it runs several hours after you turn the car off.)

If you're impatient for a particular result, you can hurry that monitor along by deliberately driving its "confirmation driving pattern". The one for EGR is shown in the P0401 code diagnostic section. It's basically a drive in maintenance mode, where you make sure to warm up fully, drive 25 to 37 mph for at least five minutes, idle for at least 30 seconds, then accelerate in B to between 25 and 37 and then do at least five seconds of foot-off-pedal deceleration in B (which gives the ECM a golden opportunity to fit the flow test in).

 

Thanks Chapman, as always great advice.

I didn't do a DTC clear (yet) just continue to monitor it.
In weekend (that round trip to my brother in law) it's up to 18's (17.95 to be exact).
But in this morning is down do 12.75 and also the minimum value changed from 0.98 to 0.51.

I'm scratching my head now...

 

I'm scratching my own head about why 'min' isn't a fixed value. Used to seeing it be something close to 1 kPa. Haven't ever seen it 'adjust' itself as low as 0.51 before.

 

Yeah, today same values.

 

Which Gen Prius? 18.xx is really good for a Gen 3 with that much mileage. I would keep checking, as sometimes you get an inconsistant reading. 13.xx is not great, but working cars with 10.xx have been reported. Definitly keep an eye on it.

Getting the EGR cooler out of the car for cleaning is a big deal. I would allow a 3 day weekend to complete the task, if you have not done it before.

 

Gen 3 manufactured September 2009.

Unfortunately I don't have 3 days for all that jazz (intake manifold, EGR pipe, EGR valve and cooler plus PCV valve and spark plugs since I'll dismantle half of car ).

But what I'm intending to do is a partial cleaning. Only intake manifold (paying attention on EGR passages of course) and EGR pipe plus PCV valve in a Saturday. I think it's doable with my skilled brother in law.
And depending on what I see on manifold and pipe I'll schedule another Saturday for EGR valve/cooler.
Looks like a good idea or not?

Thanks.

 

Nothing wrong with breaking up a big job into more manageable portions, and doing the intake and pipe is a good one to start with: cowl and wipers don’t need removal, nor do coolant lines.

That's the order I did the EGR cleaning btw: intake first, then main EGR components a week or two later. It's a good strategy; if you take too much on at once, you get punchy, start rushing, cutting corners and making mistakes.

 

Thank you Mendel. As usual great advice and documentation.

BTW, yesterday I did an 100 miles trip out of the city. 54 mpg with AC on, car just works.
This morning value is up again.



TBH, now I have no idea why is up and down like that.
But in my first free Saturday I'll do that manifold/pipe/PCV job.

 

It's not a super-tightly-controlled test. It's not like the EVAP system test that gets run several hours after you've parked and turned off the car. The EGR flow test gets snuck in while you're driving. The ECM waits for things to be warmed up, and then looks for an opportunity where you're decelerating with your foot off the pedal and above such-and-such speed, and tries to sneak the test in then, if your deceleration lasts long enough. But there can be a lot of variables in the driving conditions for a test being snuck in to real driving like that.

But it's interesting that the ECM also reports a different value for the "min" threshold. I hadn't noticed that before (though I had noticed it wasn't always a nice round number like 1 kPa). It's almost like the ECM can sort of tell when the driving conditions are likely to give it a lower test number, and it lowers the min limit too.

If you ask "how much bigger is my test value than the min limit?", 17.69 is about 19 times a limit of .91, and 12.75 is about 23 times a min limit of .56. Seems like a narrower range of variation. Interesting.

 

I'm curious to know what you all think about these values?



It's a new to me 2011 Prius with 165k miles on it. I cleaned the EGR pipe which I cleaned last weekend, but haven't got further in to it yet. I'm getting 40 - 42 mpg.

 

MPG would not be affected by a blocked EGR.

Numbers reported in here range as high as 20 and as low as 10. High is better. The numbers vary randomly a little bit so take a regular measurement and take an average. 14.1 strikes me as borderline considering you have 165k, but you might have some days where it goes down to 12. How is the oil consumption?

Exhaust Gas Re-circulation as a concept may seem backwards. Why in gods name would you want to take exhaust gasses, and pump them back into the cylinder? Wouldn't that make the engine run worse?

Well the answer is EGR is not for engine performance. The purpose of EGR is to reduce the temperature of the explosion in the engine. By mixing fresh fuel / air mixture, with CO2, the explosions don't burn as hot. You could used a bottle of CO2 gas instead of exhaust gas, but then you would have to refill another tank. Exhaust gas is free, and there is an large supply of it. Yes it is hot, but still a lot cooler than the explosion temperature. Additionally, the Prius V has an EGR Cooler, to suck heat out of the exhaust gas (helps to reduce engine warm-up time).

What is wrong with a hot explosion? Two things. The first is Nitrogen is almost 80% of the input gasses. Nitrogen oxides cause smog and are heavily produced by high temperature explosions. The second is that the engine can burn a hole in a piston if the explosion temperature is not controlled. Or a head gasket. Or both.

So what does that pressure number mean? I honestly don't know how the computer figures it out, because there is not direct way to measure this pressure. All I know is that the EGR Valve has a stepper motor that opens and closes the flow of exhaust gas. I believe it makes experiments where it opens or closes just a little too much, and measures how the rest of the engine responds. The Oxygen sensors play a role here. The actual calculated value may vary based on all sorts of things like driving style, winter vs summer etc. Taking measurements over time helps to get a reasonable picture

That said, I have seen reported numbers as high as 20 and as low as 10. High is better. My 2017 Prius V four with 42K miles is in the mid 19s. (only one measurement). My 2013 Prius V with 95k miles before any cleaning was right around 15.1 based on an average of five measurements. It is not burning oil as evidenced by the original plugs being very clean.

The Cooler was not badly plugged when I tried to blow through it, but I could barely see light through it. I bought a spare cooler on eBay, so I could compare blowing with 95k worth of crud, to freshly cleaned. I would like to find a cheap instrument that I can use to measure just how plugged it is.

My results post clean were a little disappointing. I got my first data point above 20, then the rest have been in the upper 15s. Even after a second round, where I cleaned the passages in the intake manifold (they were dirty for sure), I am still i the 15s. My current theory is that because I could not get the EGR valve apart, that my attempts to clean it were not sufficient.

 

It is logical to break it down into two parts. I did it the other way around... Plugs and EGR cooler first... Intake manifold second.

Everything that involved removing the cowl took me 3 days. If it hadn't been so hot, it might have only taken two days. Also, I did it by myself, and took pictures. The Cowl off work included Plugs, EGR Cooler, EGR, EGR pipe. Note that I had purchased a spare EGR cooler that was already clean, which did save the time cleaning the old cooler. Now that I have two Prius V's I have one spare cooler for the two cars.

I threw in an engine coolant replacement in those three days, since the car was already on stands. I discovered that there is a radiator in the exhaust pipe, behind the CAT [EDIT This might only exist on a Prius V]. With the front of the car jacked up, this becomes the lowest point in the cooling system. Loosen a hose to that radiator, you get a lot more of the old coolant out (no need to pull the under engine cover off either). I poured 1.75 gallons into the reservoir when I was done.

The Intake manifold was a cake walk compared to the under cowl work. Still very hot. Would have been done in one day, but rain Interrupted.

Taking the cowl off isn't really as hard as the videos make it look. Using a 10mm 6 sided socket makes getting all the clips off a lot easier. Give yourself the option of removing the cowl twice, rather than rush anything.

 

Thanks gromittoo, great explanations.

Since my last post I've monitored almost daily that value. Now I'm up to 17.xx kPa. Nothing changed in driving habits.
I'm all set for cleaning intake manifold and EGR pipe (I bought those two gaskets for manifold and a PCV valve, a set of brushes and a can of brake cleaner) but I must find a free Saturday to work with my brother in law.

 

There’s three gaskets connecting to intake manifold: at engine ports, EGR pipe and throttle body. FWIW, I’ve not bothered to change any of them, but this was only around 65k and 85k kms, the 2 times I’ve had it off.

 

@burebista:

You are really smart to change the PCV valve while you are at it. In spite of not consuming a noticeable amount of oil, the bottom of my IM had several tablespoons of oil. The OEM PCV valve is cheap insurance ($5.30 at my dealer), and is easy to change once the IM is removed. I forget if it takes a 21 vs. 22 mm socket. A catch can would be much better, and after seeing the amount of oil, I will eventually add one.

Here is a photo of my IM on my 95k 2013 Prius V, that is not consuming oil.


The gaskets are not that expensive. Felpro sells a set that includes the Intake Manifold gasket + the EGR tube to IM gasket for $19.99 at Autozone. I forgot about the Throttle Body Gasket, so I reused that gasket. The TB gasket does not get exposed to heat, so I am probably OK.

I bought OEM gaskets from a local dealer. Conicelli Toyota sells on the internet (at a lower price than the at the counter price), but if I pickup, I save the $14.95 shipping. Many large Toyota dealers do the same thing. Since I was buying 2 Gallons of OEM coolant at the same time (which they won't ship), it made sense for me to buy the gaskets and PCV from them. Buying the two gaskets separately from the Toyota dealer online + picking up was slightly cheaper than the FelPro set.

If you don't know already, here is my thread with photos of my "Major Surgery". I find photos more helpful than videos.
My Major Surgery saga on my 2013 Prius V. | PriusChat

 

I had a lot of trouble finding brushes that were long enough and stiff enough to make it from the EGR Tube hole to the far end. The cylinder at the far end is where I found worst buildup. I wound up buying a set of brushes from Petsmart for fish tank hose cleaning, but they were not stiff enough.

In 2015, Toyota redesigned the IM to use a "tournament" arrangement so that the path from the EGR Hole to each cylinder is the same distance and number of bends. That means the IM of my 2nd Prius V (a 2017 four) cannot be cleaned using brushes.

@Mendel Leisk recommended against doing this, but I used a fluid pump to pump Purple Power through the passages. It did the job (it contains 25% Lye), but it can attack the metal threaded parts of the IM. I thoroughly rinsed the PP off. I try to avoid using Carb Cleaner when I can, since when it evaporates, it is a Greenhouse gas.

 

The repair manual explains this. There is a Manifold Absolute Pressure ("MAP") sensor mounted right on the intake manifold. As the name suggests, it reads in "absolute" pressure, not "gauge" pressure. An ordinary pressure gauge reads zero if it's just lying on the table, because it is relative to the atmospheric pressure. Atmosphere pressure is around 14.7 psi or 101.325 kPa (sea level and no big storms coming), so that's what a MAP sensor reads when nothing is happening. A MAP sensor would only read zero in a perfect vacuum.

When the engine is running, pressure inside the intake manifold is lower than atmospheric (a partial vacuum), so an ordinary gauge would read a negative value. The MAP sensor reading is still positive, just lower than atmospheric. At idle with no EGR flow, it might be around 4 psi (28 kPa). During engine-braking deceleration it is even lower (a deeper vacuum) than that, as the engine is being spun and sucking against a closed throttle.

The EGR monitor routine waits for a nice deceleration event like that, and then opens the EGR valve some. This lets more stuff flow into the manifold, so it reduces the vacuum (the MAP reading goes up). The test value is the difference: how much the MAP reading increased when the EGR valve was opened, to whatever predetermined opening amount is used for the test.

 

That is the clearest explanation I have ever heard. Thanks. I was "Overthinking it" again.

This explains why the whole ERG path including the IM manifold passages are so important. If IM EGR passages were 100% plugged, then the EGR valve could be asked to open 100%, and yet the MAP pressure would stay very close to zero absolute pressure, indicating that the almost no exhaust gas is flowing, when there should be a lot flowing.