Prius III engine knocking at high torque low RPM (solved)

Got the error code read: OBD II code P0401 Exhaust EGR Flow Insufficient Detected.

Any suggestions now on where to start?

 

page #1?

 

The component at the head of the stream is shown in post #14 here:

Another Engine Light (P0401) question | PriusChat

It bolts directly to the exhaust manifolfIt's innards are essentially a radiator; there's 4 coolant hoses connecting to it, so removal while doing an engine coolant change would be opportune. Someone with a clogging issue has taken that off, and I believe threw in the towel regarding cleaning, just replaced it. Here's some notes on parts numbers:

EGR components:
PIPE SUB-ASSY, EGR W/COOLER p/n: 25601-37010
VALVE ASSY, EGR p/n: 25620-37110

 

OK, did take out and clean the EGR pipe. Was not that bad looking but clean now. Cleaned on the manifold and EGR side as well as much as I could. Still the same knocking in idle and low RPM acceleration. Guess I have to take off manifold next and clean it all.

 

Maybe there's something wrong with the knock sensor

 

i see. consider doing the TSB-75-13.

Introduction
Some 2010 – 2012 model year Prius vehicles equipped with a 2ZR-FXE engine may exhibit a
MIL “ON” condition with Diagnostic Trouble Code (DTC) P0401 (Exhaust Gas Recirculation Flow
Insufficient Detected) present. The Exhaust Gas Recirculation (EGR) Valve has been improved to
address this condition.
Production Change Information
This bulletin applies to vehicles produced BEFORE the Production Change Effective VINs shown
below.
MODEL ENGINE PLANT PRODUCTION CHANGE EFFECTIVE VIN
Prius Tsutsumi JTDKN3DU#C0335785
Prius Toyota Auto Body JTDKN3DU#C5474775
Prius V JTDZN3EU#C3149807
Prius PHV JTDKN3DP#C3019094
Parts Information
PART NUMBER PREVIOUS / NEW / PART NAME / QTY
25620-37110 / 25620-37120 / Valve Assy, EGR / 1
25627-37010 Gasket, EGR Valve 1
25634-37010 Gasket, EGR Pipe 1
© 2014 Toyota Motor Sales, USA

 

Good to know that there is an improved EGR but I would think I should take of the intake manifold first and clean it all up before I jump the gun? How about the sludge below the intake valve? I see some down there, going to soak it up tomorrow. I thought it might be normal as it has a drain pipe and thought it should not be the cause of any problem. But hey, going to take care of it anyway. Hope I have some results tomorrow or the weekend the latest.

 

No luck for me. Took manifold off as well and did really not look that bad. Cleaned what I could and put it all together again. Started the car and same old shaking, knocking when cold start. Let it rumble for a bit and now Check Hybrid System warning is now on too! Darn, took filter housing off again to double check if all is plugged in right. To me it all looks good. Did anybody else have this warning in combination with the EGR stuff?

I guess I do have to bring it to the shop now. EGR replacement probably on the order.

 

If they end up replacing the EGR components, good time for a coolant change, if it hasn't been done. This seems like a design failure on Toyota's fault: this thing is very hard to get to, and apparently very prone to clogging up over time.

(part no's per my post #83)

 

OK, at least the Check Hybrid warning is gone again. 3x restart did the trick as posted somewhere else.

For all future readers, I was wondering how often the cleaning of everything solved the issue at hand. I suspect not many and most probably had to do the EGR. Just speculation but would be worthwhile to find out to not unnecessary point members the wrong way. Not complaining, was worth a shot.

My Prius 2010 has 117000 miles and I thought the clogging would be the issue. Not much clogging was present at all I must say.

2016-04-28 12.20.16 (Medium) by daspi posted Apr 28, 2016 at 3:47 PM

But I guess now it is checked and even a bit cleaner.

How much work is the EGR replacement anyway? I see the quoted cost from others is pretty high. Is this doable for a driveway hack? Well did my share of mechanical work on cars... but limited time and tools.

 

25601-37010 PIPE SUB-ASSY, EGR W $245.39

25620-37110 VALVE ASSY, EGR W/MO
Replaced by: 25620-37120 $218.32

Looks like an expensive project. Then labor on top.

How about cleaning these parts? Any chance of success that makes it even worth risking doing the work twice?

 

In the Gen-4 the exhaust gas comes AFTER the catalytic converter. Much, much cleaner exhaust gas less likely to coke up the plumbing.

The Gen-4 is drawing exhaust gas AFTER the three-way catalytic converter (TWC.)

In contrast, the Gen-3 gets the exhaust gas before the TWC:

The four exhaust tubes collect in a common point where the exhaust gas tap pipe comes out (just to right of the pink tube.)

Bob Wilson

 

you can buy both of them used for slightly over $100 if you look hard. The new and improved part is going to have low miles (2012+).

really? how do you know this?

 

friendly_jacek I see some ebay listings for used ones pulled from newer models. You say after 2012 they had the updated version installed? I would love to get it used and cheaper but can these things be tested properly before installed? I would hate to pay my mechanic twice to get the job done. He might refuse to use a used part anyway. So back to the question on DIY approach. How difficult is this job?

Just found the posted manual for this job by Mendel Leisk on post #26 here:
Not just another p0401.. PICS! | Page 2 | PriusChat

 

I updated the original post but did not point out there is about two orders of magnitude reduction in emissions after the three-way catalytic converter. On the upstream side, the mixture ranges from slightly rich to slightly lean, a cycle that gets rid of the hydrocarbons, CO, and NOx. The problem comes from Gen-3 Prius that are running at high power settings, ICE rpms above 3,200 rpm and maximum EGR valve setting.

Above this threshold, the engine control laws run out of EGR valve setting and starts enriching the mixture to avoid overheating and burning out the TWC. This in turn means the exhaust gas is rich in condensible carbon compounds. These in turn can coke up the EGR valve, pipe, and manifold. So far, no one has reported the heat exchanger getting blocked but that is the first one I would expect to get coked up.

Bob Wilson

 

That all seems logical, except I don't understand why the designers didn't think of the obvious precaution of using post-converter exhaust for EGR supply in the 3rd generation. Saving the cost of the slightly longer EGR pipe that that would require? Why do other cars not have the same problem?

A few PriusChat members have already posted sagas of clogged EGR heat exchangers, although they might not have known what to call it. At least one reported giving up on trying to clean out the thing, and buying a new one.

From Toyota's published BSFC & "Operating Line" graph, it appears that limiting engine speed to 3200 RPM will limit output power to about half the engine's modest peak.

 

I'm not sure the Gen-4 solution is that much better because the TWC is integral to the exhaust manifold. I think a better solution would be exhaust manifold; bolt-on fitting to TWC, and; a pipe bolted behind the TWC up to the EGR cooler.

The problem with this approach are each joint is a leak-risk and they are subject to substantial thermal induced, mechanical stress. But at least the parts would be individually cheaper than the integrated TWC and exhaust manifold. The other risk with this approach is the TWC could too easily be gutted which of course would increase coking of the EGR and shorten its life.

Bob Wilson

 

@bwilson4web So in a nutshell, is third gen risk of clogging worse if you're high revving a lot? That's what I'm reading from your description, just to confirm. I saw minor carbon in the EGR to intake manifold pipe, hardly even describable as build-up, around 50,000 km.

I'm always driving like a pooch, hopefully that's good, lol.

 

thanks!

other cars (like the 2nd gen prius) use valve overlapping to do the EGR function. I don't understand why toyota removed the valve overlapping option from the 3rd gen and went with the dedicated EGR piping that is easy to plug in any car. maybe they increased the EGR % due to additional EGR cooling?

i rev and do relatively high speed hwy driving and still not much (i mean some, but not critical) deposits at 70,000+ miles. i credit quality gasoline.

 

Hey, want to ask one more thing to chase this issue down some more before I have the EGR changed. I have 117000 miles on mine, did not have much carbon deposits on manifold but some on the EGR pipe. My symptoms of the engine going wroom, wroom, wroom when cold start and warm up phase if way worse then when the engine is warm. Say after 10min driving it almost seems to run as usual. Maybe just harder to notice as the engine turns off when gliding and stopping. During the warm up phase the idle is horrible, very rough. Almost chocking, hesitating.

Does this sound consistent behavior for a clogged EGR valve or EGR cooler unit? And remember I had this P0401 code as well. Currently off as I reset it after all the cleaning. I suspect it will be back shortly.

Last thing, just came back from vacation, drove 750 miles in one day. Mostly highway. No issue. The week after I started having issues when I was back to my normal short runs around town.