[FIXED]2004 Audi Quattro 1.8 (AWB) No ground to control side of fuel pump relay

Nandor69 wrote:

ScannerDanner wrote: Also, because of the possibility of more than one 5v reg. You need to verify 5v on another sensor. I would pick the TPS

I just did this. And the 5v ref appears to be yet another wire. With key on I get 4.98v on a green and violet wire

You mean you are seeing 5v at another sensor. Okay that's what we wanted to see. And you say the ECM is the only module you are losing communication with? Can you talk to other modules on the network?

ScannerDanner wrote:

Nandor69 wrote:

ScannerDanner wrote: Also, because of the possibility of more than one 5v reg. You need to verify 5v on another sensor. I would pick the TPS

I just did this. And the 5v ref appears to be yet another wire. With key on I get 4.98v on a green and violet wire

You mean you are seeing 5v at another sensor. Okay that's what we wanted to see. And you say the ECM is the only module you are losing communication with? Can you talk to other modules on the network?

Yes sir. I checked four different sensors and all had 5v on them.

Yes, the ecm is the only module on the bus I can’t communicate with

EDIT: I attached pics in an earlier post of what communication looks like on one of the lines with and without the ecm plugged in.
I’m not sure if it’s much help tho to definitively determine the problem

what is the 5 volt reference doing when no comm. occurs?? if you dont have 5 volts might have to start unplugging sensors

cheryl hartkorn wrote: what is the 5 volt reference doing when no comm. occurs?? if you dont have 5 volts might have to start unplugging sensors

All the sensors I mentioned in the previous replies all have 5v on them when there is a no comm condition

The fix for this was replacing the ecm. After I had the immo flashed for the new ecm the car starts and runs great. It’s only been 1 day but the car wouldn’t drive longer than 10 minutes before it would die and not communicate with old ecm.
If something changes I will update.

Thank you to everyone and expecially Danner for chiming in and helping through the problem.

Having the 5 volt ref does mean that. But in the case of a no comm problem, having the 5 volt ref means that a sensor is not the reason for the no comm.

The title says fixed and I just read through this thread but don’t see any notes on the final corrective action. Any update to this? Thanks! 

Edit: wow. I didn’t see the second page. I’m sorry to bumping this up ??