i have a 2000 A4Q 1.8t (ATW) i've had this CEL for about 3 months now. i have been reading up on it and i finally decided to do something about it. first i took my car to a mechanic to get a smoke machine hooked up to it to look for vacuum leaks and all the smoke went straight out the filter on the leak detection pump. so they said that my leak detection pump was bad cause it should be closed while the car is off so the smoke shouldnt be going straight out the filter. so i got another pump from a junkyard and it didnt fix anything. i read up on it in the forums and everyone said the 2 most probable fixes are a new gas cap and the N80 valve (purge control valve) so i replaced both those parts and still didnt fix anything. i got my meter and checked for power at the N80 valve and i'm getting power there, but yet i couldnt get the valve to turn on so i'm not sure whats up with that. so then i bought vag-com so i can run the evap test to see what i get. well i cleared the codes, then let the engine idle for a little bit. i then ran test 070 under basic functions and it said "evap ok" so i then ran test 071 and it said "system not ok". i read a post saying to check for power and ground on the 2 wire electrical connector while your running the evap test. well first off, i have a 3 wire connector not 2 wires. secondly, you cant disconnect the electrical connector during the evap test cause then it says "open circuit" cause the pump isnt connected anymore so the test obviously wont work. so i ran the test and felt and listened to the LDP and it didnt do anything at all. so i'm assuimg that either the pump is bad or its not getting power. well i already swapped out the LDP with one from the junkyard and it didnt help so i'm thinking that the pump isnt getting power. i got out my multimeter to check for power and i couldnt find power on any of the wires....but im also not sure if i had a good ground. but my question is this.....what provides power to the pump? what fuse should i be looking at? any relays or anything that is involved in the system? where should i be looking at to search where power stops?

 

I recall reading somewhere the LDP uses the fuel pump fuse / relay.

Not sure as im trying to diagnose the same issue on my car.

 

hmmm...if thats the case then that fuse cant be the problem then since i'm definitely still getting fuel. do none of the tech's have wiring diagrams or anything that tells them where to look for this system?

 

Pete, I found this thread on vortex

http://forums.vwvortex.com/zerothread?id=2048101

Basically at the end one of the posters stated he cleaned his LDP and canister and problem went away. The canister isnt to hard to clean. Just maybe a total of 6 bolts to remove it. Maybe the lines are cluttered up ( hence the insufficient vacuum code ) I just wonder what can be used to clean the inside of the hoses.
I'm going to try and clean the hose from canister to LDP sometime this weekend or maybe even friday night.

 

hmmm, not a bad idea. but i wonder if you could use like a throttle body cleaner or something to clean out the canister and lines tho? i found a good write up last night on AW. i dont know how to post links so i'll just tell you how to find it. go to audiworld and look in the B5 A4 FAQ section. down towards the bottom you will see a long write-up for troubleshoting the evap system. its quite helpful. i'm going to dig into mine this weekend hopefully

 

Honestly, the hose going from the LDP to the canister isnt that long at all. Also, there is a ring that connects those two hoses together which tends to get brittle so i was told.

Im trying to do everything possible before taking it to the VW/Audi specialist like two blocks away from me. They know their stuff but at a cost which I dont feel can be justified if i can fix it.

I have a bentley manual so if you need any pages let me know.
email me if anything

 

i am talking to auditech79 about this issue as well and he just mentioned the fuel pump relay as well. he said he talked to a friend of his that still works for audi and that guy said the relay is the problem alot of the time so i'm gonna check that out soon. maybe you should too. right now i'm trying to search and find exactly which relay is the fuel pump relay

 

Thats what i meant to tell you. The fuel relay, not the fuse. Sorry.

The relay is under the knee bolster. You'd have to remove that part and there are a set of relays

it looks like this

 

another note I found on a VW with same issue

"1998 Volkswagen Golf 2.0L MIL Lamp on
thanks to all that replied eveyone was very helpful and every fix should be this easy!! the p1476 was for no vacuum at the leak detection pump. an air filter had been recently installed by another shop and the line from the intake to the ldp was pinched by t... Trouble codes: p1476 (man. controlled aux.emissions)."

 

yeah i swapped out the fuel pump relay and that didnt help either. i then went back to the shop and they gave me a printout on what they are supposed to do to check the LDP and we bench checked both of the LDP's i have and they both were out of limits. but then i went to another junk yard and found another LDP and checked it the same way and it tested the exact same as both of the ones i have did. so i doubt it that all 3 LDP's are bad from 3 different cars. but we also did a smoke test while i was at the shop and i didnt have a leak anywhere either so i dont know what else i could be other than the ECU not commanding the LDP on like its supposed to