Sud­den power loss

Car Mechanics (UK) - - Help! -

When go­ing over a hump­back bridge or sud­den drop in road sur­face, the en­gine power cuts in my 2009 Audi A3 Sport 2.0 TDI cabri­o­let. It’s al­most like you’ve taken your foot off the ac­cel­er­a­tor, even though there is con­stant pres­sure on it. It seems to be hap­pen­ing more and more, but there are no codes stored and the car car­ries on nor­mally af­ter­wards. Alan Bar­ton

With no codes be­ing stored, this makes di­ag­no­sis quite tricky. There are quite a few com­po­nents that could cause such a prob­lem, but a short fail­ure of one of these would nor­mally leave be­hind a fault code.

Given that it is oc­cur­ring when the grav­i­ta­tional forces are changed sud­denly, I would be look­ing for a wiring loom prob­lem be­tween the body and en­gine. With the en­gine run­ning and the bon­net open, I would try shak­ing all of the vis­i­ble un­der­bon­net wiring looms and con­nect­ing plugs. If at any point the en­gine speed drops or al­ters, this may guide you to the area of the prob­lem. It would also be worth check­ing the vac­uum pipes and air hoses in the en­gine com­part­ment, look­ing for any hoses that may move and cause the loss of power mo­men­tar­ily.

If noth­ing is found af­ter a vis­i­ble in­spec­tion, you could try con­nect­ing a di­ag­nos­tic scanner and mon­i­tor­ing the sys­tems while you’re on the road. You will, of course, need a pas­sen­ger to study the read­ings while you drive.

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