[s-cars] Help! Blown ECU fuse (what are the probable causes I should inves tigate?)

[Igor Kessel]

James Murray (QB/EMC) wrote:

> Paging all guru's and BTDT... any advice for tracking down the cause of a blown ECU fuse? I'll keep searching the archives but so far I came up empty. My car is a 93 S4. 
> 
> Yesterday (during the day), while in reverse the car suddenly died, tried restarting multiple times... nada. Scrambling to get her out of the way of blocking traffic I slightly cracked my rear middle driver side tail light in the process... don't ask it was a really really dumb ass move on my part (brain fart I guess), anyone have a replacement they could sell me? Anyway, car turns over fine, everything appears to work, but she wouldn't start!? So the possible causes start to run through my head as I sat there stranded... 
> 
> Checked all fuses on driver's side (maybe it's the fuel pump), nope all are ok. A little low on gas, maybe the remaining gas is bad? - not likely as it should at least run rough, run to get a fresh can of gas anyway just to be safe, nope didn't work.  Ok time to check for a spark, pull the coils out and low and behold there's no spark! Ok what could cause this I thought... Camshaft Positioning Sensor - oh crap not this again I thought, but damn it I replaced that 1.5 years ago... ok re-set the plug anyway just to be safe... grab a piece of wire to pull to activate the codes and start  reading the check engine light. Hey wait a minute there's no check engine light... that's strange ! Ah damn the thing must have burnt out. Of course it wasn't after a lot of frustration that I realized it was too much coincidence that the check engine light burnt out, so I started from there... luckly I was close enough to walk to the office and search on SJM site (hmmm look at that the ECU i
s !
>  fused). I pulled the carpet out and low and behold the damn ECU fuse had blown !!! what the hey? what could have caused this? 
> 
> Is it possible there's a pinched wire someplace? I recently had the front bearings and tie rods changed and I changed the driver door handle cable replaced, so I had the driver side door apart. I can't think of anything that could cause this with respect to the very recent repairs, but you never know. 
> 
> Thanks for listening... 
> 
> Cheers, /James.
> 
> P.S. What was Audi thinking putting a fuse in a location you can't check, and have to cut the carpet to get to it... of course it's not suppose to blow, but that's what fuses are for... just in case! 
> 
> BTW: So I know how to check for spark on these cars, how do you check if you have fuel delivery if stranded? (for future reference)
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James,
one of the coils has shorted its primary to GND. Check the archives on 
for a lengthy thread on the subject "sumbling, stalling, dead" by Stefan 
Richter and my post on fusing the coils individually.

-- 
Igor Kessel
two turbo quattros in the stable,
the third one is in the works