weird electronic problem S4 B5

Hi all,
got a weird electronic problem since a few days on my 1999 S4:
Drove out of the garage last saturday, when the engine suddenly died. Tried to fire it up again several times -> no way! Noticed, that the
yellow "EPC" light on the dashboard didn't come up as usual. So I got me a cup of coffee and tried again after 15 minutes: Yellow EPC light came, engine fired up! Drove the car for 30 minutes, no problem! Returned home into the garage. Thought car and me just had a bad day....
Last morning things went worse, car didn't start at all. Called the dealer, who came and pulled the codes. Told me that the power supply for the ECU temporarily failed. He pulled some plugs, cleaned some contacts and reconnected them -> Car started - fine business, read out of the codes showed no more errors. Drove for the rest of the day without any further problems.
Guess what happened this morning :-(
Maybe I should add that temperatures outside are getting lower now, we had 5 degrees below zero last night... But its definitely not a battery problem. Car has 80000 miles on the clock, ECU itself seems to be OK. Could it really be a bad contact?
cheers Bernhard
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It could be a dry joint on the pcb of the ECU. If it's cold the solder could contract enough not to bridge the gap, when the temperature rises a little it expands and contact is made. If it's on the power supply track of the ECU it would be as if the power to it had failed and therefore the fault code given.
This is just a pure guess, I know nothing about ECU's but I do know that electronic circuits can be pesky blighters now and then. In my experience look for the simple solution first, it's usually the right one. If it fails again, I would try warming the ECU up a little and then trying again. If it is still the same then you can probably rule out low temperature in that area.
FWIW HTH
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1989 UK Audi 200 QT Avant, 1B engine, 213,000 glorious miles.
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