Buzzing from ECU area with ignition on...

[skyegtb]

Hello, has anyone else experienced this? Basically when I turn on my ignition I become aware of buzzing / electrical type noise from my ECU box area. When I start the engine the noise disappears...

I recently changed my alternator and think this may be related somehow, but everything else is perfectly normal - good charging, no fault codes, no other electrical issues or issues with the car. I am 100% sure this noise has just started since I swapped alternators.

I have driven around 500 miles so far since first noticing the problem and everything is fine.

Any ideas?

[JSRS6]

1. Open the ecu cover and figure out which relay is buzzing by touching each one with the ignition on. If related to the charging circuits, the new alternator could have partially blown it. Either way, replace the buzzing relay.

2. If new relay doesn't fix the buzzing, verify new alternator is same as old one.

[skyegtb]

1. Open the ecu cover and figure out which relay is buzzing by touching each one with the ignition on. If related to the charging circuits, the new alternator could have partially blown it. Either way, replace the buzzing relay.

2. If new relay doesn't fix the buzzing, verify new alternator is same as old one.
Excellent answer, thanks. Will open the ECU cover tomorrow and check it out. The new alternator was not a genuine Bosch unit but was identical in size / shape to the old one, however the layout of the connectors was slightly different than the original although it connected up fine. Perhaps there is some subtle difference in the charging with this new unit that has caused an issue? I will check the relays and replace the buzzing one before investigating the alternator further.

Cheers, Angus

[JSRS6]

The important thing to verify is the amps.

[JSRS6]

Come again???

[4everRS]

Erik, please remove this spammer

[skyegtb]

OK, removed the ECU cover and found the buzzing relay, it is number 395, part number 8Z0 951 253. With the relay removed and the ignition turned on the buzzing has ceased and the car will still start, run and move (I moved the car from outside back in to my garage with the relay out). Can someone tell me what this relay is for? I am going to buy a new one as they are very cheap, but it would be good to know if it is related to the charging circuit or not. Thanks!

[skyegtb]

http://forum.rs246.com/viewtopic.php?name=PNphpBB2&file=viewtopic&p=408678

Found this on another forum, seems someone else has had the same problem but they never got to the bottom of what the relay was for.....

[JSRS6]

Muy interesante...
Anybody on etka see what it says that relay is for?

[skyegtb]

Just an update. Drove the car with the relay removed - all good, perfectly normal and no codes thrown on my VAGCOM. Next, re-fitted the relay and guess what? The buzzing has now become intermittent and almost never happens now!! I am stumped but this suggests to me that perhaps the relay was slightly sticky or something and in the process of me removing it it may be either completely stuffed now, otherwise working normally. Anyway, I will report back on this if anything else changes just for future reference.

[ben916]

As of 2007, that part number was replaced with 7M0 951 253C

http://i767.photobucket.com/albums/xx318/ben916_rs6/RelayandPartnumber.jpg

[skyegtb]

As of 2007, that part number was replaced with 7M0 951 253C

http://i767.photobucket.com/albums/xx318/ben916_rs6/RelayandPartnumber.jpg

Very interesting, especially the fact that this relay is for the 'additional water pump'. Is that the 'after-run' pump or something else? I bought a replacement relay as per the original part number but think I might go for the newer part if I can get it.

[ben916]

Very interesting, especially the fact that this relay is for the 'additional water pump'. Is that the 'after-run' pump or something else? I bought a replacement relay as per the original part number but think I might go for the newer part if I can get it.

Upon searching ETKA using the part number you supplied, ETKA returned the other part number... and prompted about date it was superseded.
Hope that photo helps

[skyegtb]

Well, got a brand new replacement relay and fitted it today, unfortunately this one buzzes as soon as the ignition is turned on as well. I have now decided to remove the relay altogether and see if I discover anything unusual over the coming weeks. I will VAGCOM it every few days to see if anything unusual is reported. Still wish I knew for definite what this relay is supposed to control though>...

[ramin]

Just an FYI, I heard from two RS6 mechanics that the ECU relay (labeled 395 which is the smallest of the 3 relays in the ECU box) tends to go out on RS6's and may only act up sporadically.

I picked up all three relays from the dealer and they are sitting with my extra fuses in the car. It costs around $80 for all three (with a 20% discount). Cheap insurance against getting stranded :)

Two of the three part numbers have been superseded which may or may not be due to design improvements. The other two are labeled 373 and 219.