Auxilliary air pump problems

[thepalmtrees]

1. Auxilliary air pump stays on after cold start and burns the motor out. The engine check light then stays on. Had the first one changed together with it's relay. lasted a week and stayed on, burning out the new £300.00 motor! Took it back and the garage man changed both again. This time it lasted 2 weeks and stuck on / burnt out again. This time we have had an electrical engineer recondition the motor and it works fine on the bench, but I need to know what's causing it before I dare refit it !! Any help would be greatly appreciated.
   
   Glyn

 

[Naraic]

What car do you have?

 

[thepalmtrees]

What car do you have?

Sorry I should have said ! 2005 E280 petrol, but I believe they are all a similar air pump setup.