Information on EGR system and intake Manifold Cleaning

There are a lot of different cap sizes, so you have to find one that fits

 

Fits the reservoir cap I suppose, since there is no cap on the radiator.

 

Update: Prius back on the road with all systems functional and more power than recent memory. Endoscope investigation of cylinders didn't reveal any obvious leakage but seemed fairly inconclusive. Tracked misfire down to bad coil in cylinder 4. Moved to cylinder 2 and misfires followed coil. Replaced coils in #3 and #4 with two new coils ordered online here via Amazon.ca for CAD $91 each (vs CAD$191 at Toyota). Immediately took care of the problem.

Many thanks for your advice throughout the process., Mendel and Mr. Dogman... would have been lost without you. I received the card below from my 11yo daughter in the evening, along with various gifts from my wife in appreciation. They really know me too well.

 

Nifty! I hope that resolves your issues.
Keep an eye on the coolant level. And be alert to cold start engine rattle. Also after driving and
the car sits for 30 minutes or so, it may rattle. That was my first rattle. Coolant seemed to be where
it should be. But the next day, same thing, this time the coolant was slightly lower. The mark is
right on the seem. I now keep it slighty higher.
I had planed on changing the head gasket in the next few weeks, but it decided it was time,
at 301,xxx miles.....

 

I'll keep an eye on the coolant over the next few weeks and months for sure. What causes the rattles due to gasket failure? Is it misfires due to incursion of coolant? Or?
I'll attach the endoscope images taken inside the cylinders but I can't seem to download them at present.

 

Coolant in the combustion chamber is hard to compress, and maybe fouls the spark plug as well. I think the sound is mostly at the damper between engine and transaxle, but not sure. The engine's not happy, that's for sure.

 

It’s coolant fouling of the plug causing misfires for 5-10 seconds. The engine loses sync with the transaxles motors causing a friction damper between them to severely rattle. It also causes the engine to shake. Left too long and you bend rods and blow holes in the block.

 

When the engine is hot, the gasket seems to seal. But when it cools down,
coolant will leak into the cylinder(s) overnight, (usually 1 and 2 for some reason).
And depending on how long it's been leaking, either a lot or little will sit on the top of
the cylinder(s). When the engine starts up, coolant doesn't compress so it gets
pushed to the top and covers the spark plug so it's can't spark, thus no thrust downward.
So no power, then what Parker said post #67.
If there is only a little coolant, it clears in a second or two and the engine starts. If there
is more coolant, it will take longer to clear it out, and then the new air/fuel being sucked in
can start to clean off the plug and then it sparks and off you go.
If it's really back, it can bend a rod, or two, and maybe explode the piston and throw it and
maybe the rod out the side of the engine....

That's why it's BEST to replace that head gasket at the first sign of leaking...

Also, condensation can form in the pistons when it's cold outside and a hot engine is cooling
down. This happens occasionaly and is not big deal as it's normal...

 

2010 Prius running really well since getting to the bottom of the EGR errors and a changing a couple of coils a few weeks ago. Coolant levels haven’t change in two full tanks of gas since. Mileage seemingly increased by 5% or so, and power seems somewhat increased, though this could be psychological.
All normal until CEL can back on last week. Car still running smoothly with no noticeable impact on performance. Plugged in the OBD2 which shows two DTCs: a 403 and 403P. Seems that both pertain to EGR though I’m not sure what the significance of the P is. Any thoughts on why this could be coming back? Stuck EGR valve leading to vacuum pressure in throttle body?
I removed and disassembled the EGR valve during the last round of maintenance… seemed like it was normal but I only performed a visual inspection.

 

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Neither of those is a DTC. To be a DTC, something has five characters. The first one is always P, C, B, or U. The next can only be 0, 1, 2, or 3. The final three can only be 0–9 or A–F. There can't be any DTC that ends with a P.

What scan tool are you using that displays codes in this messed-up way? Can you screenshot what it is showing you?

If you had P0403 (which you'll notice satisfies all the rules for being a DTC), that would be an EGR code. Specifically, it is a code about the electrical connection to the EGR valve, which will usually end up being something simple, like forgetting to plug it back in, or a wire that has broken at the connector.

 

Thanks ChapmanF. You are entirely correct-- the code from the OBD2 was a P0403. Sorry for the confusion. I should have had the coffee before posting, not after .

I thought it also returned a 0403 code as well, but I am now starting to doubt that in light of your comment above. I'll confirm tomorrow after I have another look. The OBD scanner I am using a bottom-of-the-line unit from Canadian Tire.

Maybe it's a short or bad connection, but when resetting the code the CEL stays off for a few days before it comes back on, with no palpable change in performance at any point.

 

P0403 has one-trip detection, so it will light the CEL as soon as it first sees the problem. Sounds like you have an intermittent electrical open or short.

 

That would seem consistent with the behavior. I’ve uploaded pics from the OBD 2 scanner.

 

Now in those pics, you're showing a P0401 code. That's a different animal.

The P0403 you mentioned before is a simple electrical issue somewhere between the ECM and the EGR valve. P0403 is immediately set any time such an issue is detected.

P0401 is a different matter. It is set by a failure of a self-test the car conducts to be sure EGR flow is adequate. The self-test involves opening and closing the valve, so it can't even be done (and the ECM doesn't even try) if there is a P0403 electrical code.

As long as the valve is electrically ok (no P0403), the car will fit in the flow test some time when you are coasting with the engine turning but not burning fuel. P0401 has two-trip detection, so the CEL does not come on until the self-test has failed on two separate drives.

 

Thanks for this helpful clarification, Chapman F. Wondering where to go next. Short history (full saga can be found earlier in the thread): 2010 Prius developed terrible rattle a few weeks back. OBD2 indicated P0401, P0301, P0303 DTCs. I disassembled and cleaned the EGR cooler, the valve, the pipe that connects it to cooler to the intake manifold, and the intake manifold itself a few weeks ago. Reassembled. Rattle persisted. Replaced two ignition coils. Rattle went away. Cleared errors codes and car has run great for a couple of weeks. Still running well but P0301 error has come back. Cleared error 2x and each time it waits for a few days and then reappears. Would seem to me that the next logical step w would be to replace the EGR valve with new OEM parts. Or am I missing something else?

 

Correction to previous post: the error that returns is P0401, not P0301.

 

All of that is symtomatic head gasket failure, coolant in the combustion chambers. and EGR cleaning, while always commendable, will not "fix" it.

Just guessing, the persistent P0401 code may due to damaged internals in the EGR valve. This:

 

What's circled in Mendel's image above is an UNdamaged ski jump. A damaged one has a rut in it, like this:

 

Pics of EGR valve are very helpful. I had it apart when cleaning the EGR loop and the pin springs back but didn't know to check the "ski jump". Seems possible that it is bunged up as the car has 150K miles on it.

Hoping it isn't the head gasket. My guess is that the EGR loop was pretty plugged up, but it was a coil that went bad that caused the death rattle. I've been watching the coolant level since cleaning out the EGR. Hasn't moved after burning through 3 tanks for gas, nor has there been any sign of a rattle at startup (or anyother time since replacing bad coil), or white vapour out of the tailpipe. I have not pressurized the coolant system to check for leaks though. Apparently Canadian Tire has the kit as a loaner but I don't really trust myself to run the test accurately.
At any rate, a bad EGR valve "ski jump" seems most likely to me. Is it foolish to do this before pressurizing the coolant to check for bad gasket? And am I correct that changing the valve requires removing the wipers, tray, and entire EGR cooler?