Smax Parking Sensors Issues

[imy9]

Hi everyone new member who knows very little about cars looking for some advice.

I have purchased a 57reg Smax 2.0tdi titanium from a independent dealer on Friday, got home and noticed that the front and rear sensors do not work! Have taken it to two independent garages and both, having completed a diagnostic have said a fault is not appearing on the tool that they are using. (they note however that there is clearly a problem).

The strange thing is that when I turn the key twice in the ignition- lights appearing on the dash- the sensors work! They recognise things at the front and back, have also checked each individual sensor and it does respond. When I start the car lightsoin the dash which says "on" light on for a few seconds then switch off, put it in reverse makes a beep noise for a few seconds then off again, Any ideas?

I can take it back to the dealer but thats a 200 mile round trip and have to leave it there for a week AND pick it up again.

I can go to a ford dealer, which would cost £65 for a diagnostic- is the problem going to appear on their machine? I could then get a local garage to sort out the repair??

Sorry to drag on but this has been causing me a major headache and I start school again next week (am a school teacher) so want this sorting asap without it resulting in me selling a kidney on eBay! Thanks in advance Imy.