my A6 AEL wont start & making odd noises

[MGaz]

The AEL in my A6 C4 tdi quattro is playing up. drove all the way home fine yesterday, then started to drive down our hill/track and it stalled on me. then it wouldn't start so i bump started it, then it stalled again . Tried to start it again and it was revving high, up and down about 2.5k-3k rpm then died. I couldn't start it after that and every time i put the ignition lights on it was making a constant strange electrical sound under the bonnet. The car was still on a slight slope at this point, facing down hill. I fired up the typ85 Coupe quattro and toe roped the C4 back up the hill again for a bump start. but still no joy

So we rolled it in to the yard on to the flat, and i put the ignition lights on again and the strange noise under the bonnet had gone away and it started..

I then reversed it back on to the slope facing downwards, and it died and wouldn't start and the strange electrical noise under the bonnet had come back again.

So... It seems my car no longer wants to drive down hill

Any ideas? what the hell is going on?

[Monkeymagic]

Get it plugged in and pull any fault codes first.

[MGaz]

I noticed there was a bit of water in the rear passenger side foot well a few days ago, but thought someone might have spilt a drink. Then yesterday on the way home before it started playing up I thought I could hear water in the centre air vent when the fan was on. Then my girlfriend said water was coming out by her foot every time we went round a right hand bend. So I lifted up the two front mats and the floor is wet on both sides. Doesn't smell of anything I don't think. Also I just remembered seeing a wet patch under my car the one day where it was parked over night and a tiny bit of dripping near the bulk head underneath.

I also noticed yesterday that there was a lot of condensation under the rear seat where the battery and other electric boxes are ????

[diesel des]

Wet ecu? Or low on diesel? Could be drawing air due to a cracked or perished pick up line? When the pumps are empty they are more noisy.

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[spink]

Pull up the black plastic drip tray at base of windscreen (only visible with bonnet open) take a look and see if its got any water lurking beneath

[5cylinderman]

Pull the passenger's side toe board and check the multiplug at the ECU. Courtesy of a blocked N/S/F sunroof drain tube and a blocked scuttle panel drain, my old C4 Avant had a small swimming pool in the footwell and green terminals at the ECU. A can of contact cleaner and a toothbrush got it sorted out.