occhis

I'd like to take a different direction on this and check the relay that controls this system. It is relay J757, which is located in the left side electronics box under the hood. I have tried more than once to remove the cover on this box with no success. Can anyone offer up detailed procedure (pics would be great) on how to remove the cover without risk of damage to the cover?

frankinstyn

Hello everyone. So I've had this problem for the last two years. Sadly this year I needed to pass emissions so I had to get this fixed no matter what.

I have changed over that period

N80 Valve (3 times)
Gas Cap
All emissions lines and vacuum lines
All vacuum line check valves
Charcoal Canister
Emissions pump assembly (bought as whole unit rather than just the pump)

Finally I brought it to an independent shop and had them fog the whole system.

They tested for a week and couldn't find any leaks anywhere. They checked all my connections and electrical to see if I had done something wrong to no avail.

So I went to the dealer and bought another N80 valve and popped it in. I then drove 200 highway miles and drove strait to the emissions station....and passed!

The light stayed off for the whole next tank.

Sadly it has returned. I think that there is in fact nothing wrong with the emissions system. The light only comes on when I take it for short drives (10-15 miles).

Thankfully I have a bluetooth obd2 adaptor and the 'Torque' program on my phone so I can clear it in about 15 seconds. Still very frustrating though.

A6Gary

Your experience is quite interesting for this problem. I've also been having this DTC for some time, and have done the following: replaced the N80 valve and verified the new valve is not leaking with my vacuum pump, verified the LDP resistance and voltage are both within specs, and verified that LDP runs via the output test in VagCom. But the EVAP test in the Basic Settings (071) aborts when it tries to run the test. So, I am going to try to see if a I have a leak somewhere (maybe a bad gas cap also). With only 74.5K miles on my '06 A6 Avant, I doubt that any of the vacuum lines have become brittle yet. BTW, I'm also in in Pierce County area, near Lake Tapps.

ILLusive

Tony(milan_o) has accessed this box at least a few times. I'm sure if he can chime in, he'd help you out. I've pretty much gone thru the motions similar to what frankinstyn has done over the course of a few years and am still stuck with this Godforsaken code! I know Tony has even gone to the great lengths of swapping a new ECU and reprogramming it but the code eventually came back. Its got to be some kind of electrical issue someone hasn't narrowed it down to and your guess that the problem may be rooted from the relay box might be it. My mechanic also had the same suspicion but did not have the time to investigate.

A6Gary

I found and attached the Audi Self-Study Program (SSP) 941903 that provides information for the EVAP system, and how to diagnosis problems with the system. Although a number of us having this DTC issue have tried some of the fixes identified in this document (without success), it also contains additional tests that you can perform on the EVAP system to narrow down the problem(s). Note the additional leakdown test described on Page 22 in Display Group 137. I will trying these procedures in this document on my A6 Avant to hopefully fix this problem once and for all.

milan_o

Here is a link to instructions on how to get to the box:
https://www.dropbox.com/s/4e0wknis7i...amber.pdf?dl=0


I have put in the following new parts: LDP, N80, J757 relay, gas cap, vacuum tube. The ECU was a used one.

After investigating this on and off over the last few years I currently believe that this is a vacuum related issue.

When I run the LDP basic test using VCDS the reed switch never shows as open. On the rare occasion that it does pass the test I am able to see a the reed switch open for a moment a few times during the test using VCDS. Based on the doc that A6Gary posted, there are 3 requirements for the reed switch to open. Consistent vaccuum applied to the pump, Batt+ voltage at pin 3, and the ECU to pull pin 2 to GND on a 60/40 PWM.
Of the 10+ people on AW that have had this issue, the only confirmed fix has been a replacement of the vacuum tube. There are 5-6 of us that that did not resolve the issue.

My plan now is to test for consistent vacuum while the test is running and test the N80 valve for leaking.

occhis

milan_o
thanks for the link

A6Gary

I been having the DTC appear for months, and haven't been able to determine the problem that triggers the fault. So, today, I again checked out the LDP system and performed the following inspections and checks:

* There was no significant dirt or dust on the LDP air filter, and it appeared to be unrestricted.

* I unbolted the LDP and the outlet hose so I could check the P/N of the evaporative emission canister. It is the updated part - 4F0-201-801-B, which is what ETKA 7 says should be installed for MY 2006. I then verified that it is not restricted and allows airflow.

* With the outlet hose disconnected, I ran the 071 output test, and verified the pump was working by feeling the air pulse on the outlet hose. VAG-COM indicated that there was a "Large Leak", an obviously result with the outlet hose disconnected.

* I reconnected the outlet hose and re-ran the 071 test, the VAG-COM indicated "System OK".

* I re-ran this output test several more times and the results were always "System OK". During the test, I could hear the evaporative emission charcoal canister "pop" to relieve the excess pressure. These results compare with the previous 071 test results of "ABORT", and I never got a "System OK" test result.

With the results I had today, I can't say exactly what the problem was with the EVAP system for all of these months. It might have been that the reed valve was stuck so when the outlet hose was open, the reduced restriction may have allowed the valve to work again. Or maybe it was some other restriction that would not allow the LDP to pressurize the system. In any case, the EVAP system appears to be working as it should. The only component of the system I replaced several months ago was the N80 valve. If the DTC doesn't appear again, then the system has been "fixed", and restored to its operating condition. Time will tell.

occhis

Is there another way to activate the LDP, as I do not have a VAGCOM tool. Will merely starting the engine with the outlet tube disconnected achieve the same result?

A6Gary

In order to activate the LDP, you will need to access the ECM, which may only be done using a VAG scanner (like a dealer) or VAG-COM.