NefMoto

I've recently finished swapping an ATW into my '99.5 A4 2.8Q, running a CM box and an ATW harness with a wideband plug wired in and a resistor for the VVT tensioner. There's still one issue that I can't seem to figure out, which is the DME relay never opens once it closes, leading to the DME never actually turning off. I get B+ and IGN+ at all the proper pins at the body plugs and the relay itself is fine. At first I used an ATW relay, then an AWM relay, with no change. If I pry open the contacts while the key is turned to off, it pops open and stays that way. I also stalled once and it seemed to turn the DME off properly because the throttle cut on clutch press magically started working and stopped again after I cleared codes.

Has anyone dealt with anything similar? What I would really like to understand is how this relay actually works and under what conditions does the DME ground it. I didn't make any modifications between the relay coil and DME, the only thing I did in that circuit is used what was once the SAI pump power wire at the body side of the plugs to power the relay because the original wire was too thin. According to the Bentley wiring diagrams both run straight to 30 so I see no issue from that. I get 12v across the relay coil until I turn the key, then it drops to around 0.9v until I open the relay manually, at which point it goes backs to 12v and stays that way even if I close it. That doesn't seem right, but without knowing how the relay works I'm walking blind. I tried translating the section of the FR (pg.1485) but it doesn't make much sense, what I can understand makes it seem like it explains everything I need to know.

i have seen bentley wiring diagrams wrong.  do you have a pr code? such as J89 or a part number. i can try to get factory wiring diagrams for you and give suggestions ,but what is the DME relay i have never heard someone say that?

DME relay, ECU relay, motronic relay, tons of different words for the exact same thing. I'm actually looking at factory wiring diagrams, got them straight off ELSA, they're just made by Bentley from what I understand.

Small update, the DME now turns off, eventually. If I park the car and come back after a few hours the DME will be off (no communication), if I turn the key to on and then back the DME still stays powered. But now communication gets interrupted for a moment while turning the key when the DME is still powered. Throttle cut on clutch in seems to be working consistently now, so something has changed. I'm still stumped though, I haven't gotten anywhere in figuring out the issue.

Is the relay grounded directly in conjunction with the IGN+ pin being powered, or is there some electronic trickery going on inside the DME just using that as an input?

Still trying to figure this out. I saw in a thread somewhere ddilenger mentioned using a diode before pin 21 of the ecu connector when running an immo-equipped ecu in a non-immo car to prevent it from running after the key is turned to off. I figured it would apply since I had to immo defeat the ecu I bought before I could do anything to it. On my first try I screwed it up and pointed the diode the wrong way, the ecu turned on and I could connect with vagcom but the car didn't start, the fuel pump relay never closed. But the ecu did shut off as soon as I turned the key to off. I reversed the diode and now I'm back to square one, ecu doesn't turn off again. Since I still have next to no understanding of the circuit I don't know what to make of this, but at least I seem to be getting somewhere. Given that it does turn off with the diode backwards, is this issue with the relay circuit or something else entirely?

I've also heard of removing/bypassing this relay and now I'm seriously contemplating it, but I don't know how to go about doing this. I know that I'll have to code out diagnosis, that I can do no problem. But what do I do in terms of wiring? And how will I then power the VVT solenoid? Ideally I'd like to keep the relay since I want to avoid hacking up my engine harness, but if there's no other way then I'll do it.

Took me 2 diodes to prevent the ecu from staying powered on.

Details please?

Well, whenever I convert an 00 car to 01 ecu, I have to power pin 21 manually. I get power from fuse 7 (10A) in the car. Without a diode the car will keep running for a few seconds after key off, which causes all sorts of codes due to everything else shutting down. I found that 1 diode cured the problem 70 percent of the time, but 2 eliminated the issue entirely. Both inline of pin 21.

Oh I see, so you cut the wire from the relay to pin 21 and powered it manually?

MY2000 4.2's didn't have a wire in pin21, I had to add it manually.

I'm talking about running ME7.5 in a '99.5, I'm using an ATW harness so it originally had the relay and a wire to pin 21. I didn't realize you were talking about the 4.2, but it still seems like everything you said will apply. I guess I'm going to try the second diode with the relay still in place, if that fails I'll get power from the fuse like you said.

Take power from 75x, run 2 diodes inline, and feed pin 21 that way. See what happens.

That actually does seem easier than messing with the relay again, I'll have a go and hopefully it works. Will this trip a code for the relay diagnostics?

If it works, and it does (throw a code) I'll send you a file with relay diagnosis removed.

That won't be needed, I've made a couple of changes to the bin already so it'll be easier if I just do it myself. I was just asking out of curiosity really. I seriously appreciate the help, hopefully I can finally get this damn thing working properly.

Finally did it, I ended up having to use fuse 7 to trigger the existing relay, don't know if the diodes were actually needed but I'll keep them there since it's not hurting anything. No code for the relay either AFAIK. I can't thank you enough, you just put an end to almost a year of fiddling and troubleshooting that was driving me crazy.

Glad to help! This is how I do it, sans the relay. I would think when using it the diodes aren't necessary, but if it works, it works :)