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-   -   4.2 tdi hot start problem (http://forum.a8parts.co.uk/showthread.php?t=15077)

velour 1st July 2019 12:12 PM

4.2 tdi hot start problem
Hi all,

Having an ongoing issue with my 2010 (D4) 4.2 tdi and thought I'd ask if anyone has any ideas.

Issue is that it starts from cold no problem, runs fine and happy for 2+ hours on the motorway. However, as soon as I stop there is a high risk that the engine management won't let the engine start again.
The engine fan starts going at max and when the start button is pressed alomst every fault code displays on the dash in sequence (ESC, TPMS, air suspension, diff etc) and the car won't start.
However, as soon as the fan stops everything is OK and the car will start, but the hotter the external temp the longer it takes the fan to stop.
It's also the case that, if the car is hot, just firing up the electrics (e.g. opening a door) will cause the engine fan to come on even if it had stopped previously.
Recently it's been running the fan so much it flattened the battery.

VCDS doesn't reveal anything so wondering if it might be something to do with a temp sensor on the way out?

Any thoughts on what it might be and how to check?

Many thanks.

Joe2.0E 1st July 2019 03:20 PM

I would start by disconnecting the electric fan for a bit and see if it eliminates the issue.
I had a faulty fan module on a D3 3.0tdi a few years back and the fan just started running incessantly until it flattened the battery. No isuue with car overheating whilst fan was disconnected for a week or so whilst waiting on a used part to come by post from a Dismantler in Germany.
Fan runs mechanically whilst engine is running anyway without electrics.

velour 3rd July 2019 09:40 AM


Thanks for that - hadn't thought about the electric fan supply. Will check that out.

Car is currently in the local garage, they have checked all the sensors, wiring etc and cant see anything out of place. Current thinking is that the ECU is fried and needs replacing!

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