Audi 200 3B and S2 3B ECU question

[shone190]

Hi guys, does anybody know is there any difference between Audi 200 3B and S2 3B ECU?

I know that they have different part numbers, but are they interchangeable?

Thanks.

[_ShurikeN]

They are interchangeable. There may be software difference between them which none of us would feel, i suppose.

[Hallacaso]

another question regarding this matter
I recently purchased a 3B S2 ecm from over in Belgium for my 1990 CQ with a 3b out of a 200, but unfortunately the s2 ecm will not start the car. Any ideas? I’m just to figure out if the euro s2 ecm is plug and play?
Perhaps I just bought a bad ecm and was told it was good…
Thanks for any information

[K Simmonds]

There's a resistor that fails quite commonly that can cause the ECU not to start the engine, the other thing to consider is if the ECU you purchased has an imboliser... However I don't think 3B ECU's have this feature.

I'd do the normal tests to see if it's trying to start, ie... Check for spark and fuel and go from there, 3B's are very fussy about where the dissy is, have you adjusted that at all since fitting the new ECU?

I'd also have a close look at the main ECU plug to check for corrosion on the pins, I've been caught out by this in the past.

[Hallacaso]

Thanks for the information, I tried it a while back and when it didn’t start I just put the old one back in. I definitely didn’t mess with the distributor at all. Is there a way to check the ohms on the resistor to verify that it is functional? I will put the ecm in again and see what I’m missing fuel/spark. Thanks for the input.

[K Simmonds]

I can't actually recall which resistor it is, if you drop Newsh a PM he'll tell you as I know he's dealt with it a couple of times. Fortunatally I've never had to change one myself. If he see's this post I'm sure he'll tell you straight away which one it is.

I have to ask what happened to your orginal 200 ECU, what caused that to fail, or if you still have it will the car run with that?

If you haven't moved the dissy that's great as you can rule that out, however have you changed the cambelt as if that's a tooth out it's pretty much the same as having the dissy in the wrong place and the car won't start. The other sensor that will prevent starting in the one for the crank, have you had it appart to change the clutch? Sometime's the pin on the back of the flywheel get's snapped off which will prevent the car from starting, though you have to be very rough with it cause this issue.

Sorry for all the questions, I'm just trying to help remotely which obviously isn't as simple as if I knew the cars entire history and could actually work on it.

Though it's normally something simple that's causing a non start, has the the car been stood for a long time? If so being a C3 the fuel pump may not be working as the tanks metal and sheds corrosion into the bottom which kill's the pump... You should be able to hear it prime when you turn the ignition to the start position.

This is a really simple one, has the car got a decent battery fitted? It needs to crank over fairly fast to start, I can't recall the exact RPM but a lazy battery won't start the car.