Starting problem

[Kevin Adams]

My 2007 Q7 started ok but drove for a while stopped at a shop for about ten minutes then wouldn't start It's sluggish to turn over or won't turn over at all. It seems if I leave it off for a long period it will start!

Can anyone help please?

[Bigdave1230]

Crank shaft sensor. 
Car will start and drive fine then when it starts to get warm and you park up the temp under the bonnet continues to rise as there’s no air flow. The faulty sensor gives an implausible signal when hot so when you try to start the car again the engine doesn’t get the correct position data so will either turn over and over or turn over for about 2 seconds then stop cranking just like it would if it had started correctly. Can be really intermittent and won’t show any fault codes in vcds. Leave it to cool down and it will fire up fine. Happened on mine last year

[Bigdave1230]

Could also be the starter but that’s a 4 hour nightmare of a job. If it’s not turning over at all I’d be more inclined to think starter thinking about it

[Kevin Adams]

37 minutes ago, Bigdave1230 said:

Could also be the starter but that’s a 4 hour nightmare of a job. If it’s not turning over at all I’d be more inclined to think starter thinking about it

Thank you that sounds plausible. 

[Kevin Adams]

43 minutes ago, Bigdave1230 said:

Crank shaft sensor. 
Car will start and drive fine then when it starts to get warm and you park up the temp under the bonnet continues to rise as there’s no air flow. The faulty sensor gives an implausible signal when hot so when you try to start the car again the engine doesn’t get the correct position data so will either turn over and over or turn over for about 2 seconds then stop cranking just like it would if it had started correctly. Can be really intermittent and won’t show any fault codes in vcds. Leave it to cool down and it will fire up fine. Happened on mine last year

It acts as if the battery is flat. It will start with jump pack

[Bigdave1230]

Have you tested the voltage with a multi meter on the jump points under the bonnet on the passenger side? I’d measure there then get the negative jump lead and connect to the negative terminal and clamp the other side to somewhere meter on the engine. Then measure it again and see if there’s a difference. Test it with the engine off and then with it turned on. Even 1 volt is a big difference. Should turn over quicker with the jump lead connected. 

[Bigdave1230]

Metal not meter