P0402 troubleshooting (EGR Excessive flow detected)

I saw an earlier post describing the process of cleaning out the intake on TDI engines and after hours of reading and trying to educate myself on the intake system I decided to follow the instructions listed here (which by the way is damn informative & accurate)
http://pics2.tdiclub.com/gwillie/VW/Sballintake/INTAKEMAN101b.htm


My EGR valve and intake were pretty gummed up. It wasn't nearly as bad as the ones i've seen that were 80 - 90% gummed up, but still it gave me hope that if I cleaned it out, maybe I could get away without replacing sensors.

After successfully tearing apart the intake ( a first for me ) and cleaning out all the crap ( another first ), I managed to successfully put everything back together and start the engine. to my dismay after driving a mile the check engine light came back on with a P0402 error. Without a bently manual and VAG-COM i'm left to search the internet and this site. So far I've not found any decent troubleshooting information, or even what sensor could be faulty.

There have been no noticible symtpoms such as powerloss or any other documented issues associated with EGR errors. The only thing that even hinted to an issue was the CEL (idiot light) coming on. After I took the car to AutoZone to have the code read, I proceeded to search for potential answers.

In the end, i'm back at the beginning, except this time I have a clean intake & EGR valve. If anyone has any tests I can perform on the sensors themselves, I have a multimeter... and am willing to get my hands dirty.

I would pull off the egr again, and use a mityvac to pull a vacuum on the egr valve. this will pull the valve off of it's seat, you will then be able to thoroughly clean it.

this could be your problem

let us know if the mityvac holds vacuum

alpha, do you have any other suggestions if the EGR is clean, the mightyvac holds vacuum, and the problems still persists?

someimtes a bad MAF will make the egr do werid things

Interesting. Same thing happened to me. Now I have a weeping EGR after the intake cleaning. I may just buy a new one.

I'm not sure if mine is weeping, but I do know that after cleaning the egr, the car is okay for about 20 miles, then the damn CEL comes on again.... I might just replace the damn thing and be done with it. CELs bug the hell out of me. . .

Same here, but I'm not convinced it's due to a faulty EGR.

I build a block-off plate last night, put it between the EGR and the 90* tube... and it STILL comes back 'EGR excessive flow.'


how ZERO FLOW can be excessive, I'll never know.

also, i have two different MAF's, bolt yield 800+ on the WOT test in 3rd year, both allow the engine to rev to 5000+ (drivebiwire test), but both cause the 'actual vs requested' flows to be different.

I don't have VAGcom here, but I'll be very upset if the actual vs requested is different now. That means there's a leak somewhere in the system as there is NO WAY the EGR is getting flow now...

So the 50,000 questoin is, how can you determine if the MAF or various other sensors are bad?

Is it something where you can measure reistance via a multimeter?

Watch the numbers using a scan tool to ensure that they make sense. You will need not only the scan tool, but also knowledge of what the numbers are supposed to be under different load conditions.

GoFaster said:

...but also knowledge

Click to expand...

well... I'm out.

Okay a quick update...

I got a vacuum pump and verified that the EGR valve is operable. So my next guess is the N16 solenoid valve ( i think that's what triggers the EGR valve to open/close ).

What exactly causes this blasted EGR error? I have a Vagcom cable now, and it shows intermittent... I have not seen any decrease in power, I just have this blasted CEL.

What about epsilon? If replacing the solenoid valve doesn't fix it, what other pieces can I check? I mean, how does the computer know that there's excess exhaust flow in the first place? Is it the sensor that connects to the CCV outlet on top of the engine (that connects to the air intake)?

balaaaaaaah i hate CEL's!!!

if you had to unplug any wiring connectors pull them apart and check the pins. sometimes if there hard to undue you spread the connectors and they dont make good contact anymore.

I'll check the connectors this evening to see if they've been jacked up on the solenoid valve for the EGR. Hopefully that's notwhat it is.... I'll keep ya posted

GardRail said:

Okay a quick update...

I got a vacuum pump and verified that the EGR valve is operable. So my next guess is the N16 solenoid valve ( i think that's what triggers the EGR valve to open/close ).

What exactly causes this blasted EGR error? I have a Vagcom cable now, and it shows intermittent... I have not seen any decrease in power, I just have this blasted CEL.

What about epsilon? If replacing the solenoid valve doesn't fix it, what other pieces can I check? I mean, how does the computer know that there's excess exhaust flow in the first place? Is it the sensor that connects to the CCV outlet on top of the engine (that connects to the air intake)?

balaaaaaaah i hate CEL's!!!

Click to expand...

My valve was the N18, not N16 (2001 Jetta TDI).

Regardless, it was about 45 from TDIparts.com and I don't get a check engine light anymore. So, I blame it on the valve or a bad connection (vac or electrical).

heh i wonder if I can stop in at the stealership and ask them if I can borrow an N18 to see if that fixes it. I know, I can act like i'm willing to pay 500.00 for it, then drive off after verifying that it's the N18 ;-) heh

45.00 isn't all that bad considering it will make the CEL go away

GardRail said:

45.00 isn't all that bad considering it will make the CEL go away

Click to expand...

I believe the valve is over 100 at the dealership... 45 is from tdiparts.com

heh wish I knew someone that was close by that would consider letting me borrow their valve to see if it will make the CEL go away...

I'm in the same boat. Cleaned the intake, NEW egr, NEW air mass sensor, still have p0402 code. I was thinking about trying the N18, now I will for shure.

N18 solenoid

Dirty Pile said:

I'm in the same boat. Cleaned the intake, NEW egr, NEW air mass sensor, still have p0402 code. I was thinking about trying the N18, now I will for shure.

Click to expand...

Have you tried testing the N18? I am getting the p0402 intermittently (and clearing it with the Scanguage) every couple of days, usually when cruising at low rpms. Today I took my N18 out of the car and tried sparking it with a 12volt source and i did not hear the solenoid move. I took it appart and cleaned it and put it back together and tried sparking it again and now it makes a happy clunk noise everytime the solenoid is energized. I am hopeful it will work when I put it back in the car (as soon as the temperature outside comes up above freezing, next few days maybe). I did this procedure on an N75 that got it working again. I took pictures, anyone interested?

Yes post pictures of both
This is good stuff

N18 Cleaning

I have posted pictures of the N18 cleaning (N75 is exactly the same inside) check them out on my ride judge page...

N18 Cleaned and operating!

Check out the video: http://www.youtube.com/watch?v=bGcZExWof8U

I installed it but I still get the p0402 code intermittently, once a day... I clear it with the scangauge and it comes back a few trips later. Would be nice if you could set the scangauge to automatically clear certain codes when they appear!

My next step is to get a Mityvac type hand pump and gauge to verify the vacuum coming from the N18 when the vehicle is running and I am watching VAG-COM. Also I would like to use the hand pump to verify at what vacuum pressure the EGR valve opens. Gotta love the TDI, great excuse to buy tools and learn stuff.

If all of that checks out then it is possible my MAF is simply reading too high (idles at 500 when requested is 370) this is my third MAF tho so if its just EGR problems i'm not changing it... I had another maf that read too high that I rotated in its socket until it read lower at idle, maybe I will dig that one up, I only changed it because I was having limp mode issues which turned out to be turbo related (N17 valve and VNT actuator).

And my car is totally stock other than than the power box I plugged into the injection pump harness! I would try disconnecting it to see if it made a difference but is should not, it only affects fueling, and driving without it is unbearable!

bah i dont know... it sounds like this issue involves swapping out parts in a troubleshooting shotgun effect.

Interestingly enough if i remember correctly this started to happen after placing a little too much ATV fluid in the fuel filter the last time I changed it out. The car smoked like a @#$%^&*^%$#@#$$%^%#@$$. It was immediately after that the CEL started coming on.

The exhaust manafold cleaning seemed to help some, but ultimatly I think there's dirt somewhere over some sensor further down stream which is causing the computer to think that there's too much exhaust gas...

your problem is a flow problem the most probs I see with the valves is they are broken from people playing with them its most likely the egr valve not seating properly (you cleaned it right?) pull intake boot and hook vacum gauge to egr valve pump it up and clean the seat and cup then pull vaccum line off with vaccum and let it snap into place a few times and try also check the exuast lines going to cooler may have a leak .....

I finally got my N18 valve but I never got to put it in. The same week I received it my injector pump started leaking, or should I say hemorrhaging, so I took the car to the boys at Fix Um Haus to get it repaired. While it was there Rich set the timing ("on the high side") and replaced a couple of vacuum hoses. Happy to say the CEL has not been on since (2 weeks so far). Can't really say what exactly fixed the issue, other than it was not the N18 because the brand new one is sitting in my garage.

probably the vacum lines fixed it ...

dr.diesle said:

probably the vacum lines fixed it ...

Click to expand...

WAY COOL!

I have about 1 meter of vacuum hose laying around in the garrage


I've already taken a mightyvac and attached it to the EGR to verify that it operated correctly (and it did). I cant remember if i throughly cleaned the seat where the plunger meets the casing which could cause a leak.

Interestingly enough, when I start my car in the mornings, the light is off, backing out of the driveway it stays off, but the min i put it in drive and accelerate the light comes on and stays on.

The crying shame of it all is I think I lost my vagcom cable!!!

damnit to hell...

P0402 Diagnosed!

Finally diagnosed my P0402.... EGR valve doesn't open... I checked and pleanty of vacuum going to it, so I took off the 90degree bend rubber hose that goes to it, started the engine (watch out, egr sucks!) and plugged in the the vacuum hose to the EGR and un plugged it, the valve does not move at all. I also noticed that if I Tee into the vacuum line to the EGR valve that there is no vacuum present unless I block the line on the EGR side of the Tee: that means that there is a hole in the EGR vacuum diaphram.

I decided to remove the vacuum input to the N18 valve to eliminate the system (and the vacuum leak, which I think the N18 would have prevented from affecting the rest of the vacuum system anyway)

So back to the original question. Why does it say P0402 EGR EXCESSIVE FLOW? Because the only place the ECU can measure flow is at the MAF (mass air flow) sensor near the air filter box. When the ECU sends a command to open the EGR valve then the engine will SUCK a percentage of air from the exaust and LESS air from the airbox. It SHOULD see the difference as a reduction in ammount measured by the MAF. When the EGR is not working there appears to be EXCESSIVE FLOW from the MAF.

P0402 ... continuation... sorta?

OOOoookay... after being frustrated with the blasted MIL for a while, I went ahead and got a replacement *ag-com cable and started logging information. Yesterday morning I came into work with the MAF unplugged completely. It gave about the same performance (maybe a bit worse) than what I had with it plugged in...

After checking the codes I found out a few things... doing that really pissed off the computer and caused glowplug 4 to wig out (gave a code), I still had the P0402, but then I also had the undercurrent soething or other error relating to the MAF... I cleared those codes, plugged the MAF back in and proceeded to log some measuring blocks for the trip home. I'm not too keen on the information but I did see a difference between measured and actual air flow for the EGR... (whatever the heck that means)...

Anyways, When I got home, I decided to open up the hood again to inspect all the valvues and vacuum hoses while the car was on. I took the mighty vac I had and plugged it into each vacuum supply which connected to various T's or other solenoid valvues and found that vacuum was getting to the EGR anti-shutter mechanism... When I looked at the hose that connects the mechanism to the final solenoid (whatever it's called) i noticed that the outer sheething was brittle and a fine powder was plooming every time I moved that section of hose closest to the solenoid. To remedy that, I broke out my pockent knife and cut off a 1" section of hose and plugged the anti-shutter valvue back into the solenoid.

The good news: No MIL light this morning AND i have a vagcom log of before and after... Maybe someone on here might be able to help me to understand what the measurements mean, and what ratios are good?