We have a 2012 Mk3 Diesel which we've owned for just over 18 months. There's a start button on the dash, marked "Power" and until recently this has always worked as follows .. press and release without touching anything else, switches electrical systems on or off. Press and release while clutch is depressed starts the engine. Just a short press.

Recently it's started behaving differently. First a couple of months ago it started to need the brake pressed as well as the clutch, and putting up an error message if you didn't. It needed both, it wouldn't start with just the brake, or just the clutch, pressed.

Now today, new behaviour. A brief press, with clutch or clutch and brake pressed gives either (1) a brief cough as if trying to start, or (2) no attempt to start, electrics come on and an error message telling me to switch off  or (3) very occasionally normal starting.

By trial and error I've found that I need to hold the button pressed and it starts right up. 

Do any of these strange symptoms ring any bells?

Before I found that holding the button pressed did the trick, I thought it might be the battery, even though that's quite new. But actually when it does start it turns over briskly and fires instantly, no indication of low power or poor contacts anywhere.

And the "Power" button clearly makes contact as well as a brief prod always triggers "something" even if it's not what I wanted.

Thanks.

The clutch pedal depressed switch has totally failed.

There are two switches on the clutch pedal, one to tell the car when the pedal is fully released and one for when it is fully depressed. The two switches are not the same part number. Given the very recent change in behaviour, I would replace both. 

Thanks, that makes sense there being two switches. So I presume it knew the clutch pedal had been depressed a bit, but without the fully depressed switch as well it needed the brake before it would start.

Although it's not doing this now. Since the latest change it's never asked for the brake. On Forscan I can see the two clutch switch statuses changing as I move the pedal down.

I'm wondering if the current behaviour, needing the button held pressed until the engine has started, may be some sort of low voltage thing. If so it's disappointing there's no error display or anything logged.