Sudden power loss

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.