Two weeks ago, we drove our car (Mondeo Zetec 2.0 Petrol, 2002 model) to Penzance from Oxford (~280miles).

On the other morning when we just started our journey back to Oxford from our hotel in Penzance, after only half a mile driving, the speedometer suddenly stopped working.

And the car then became bumpy occasionally, like the bumpy you feel when releasing clutch too fast when switching gear. It only happened once or twice every 10 mins or so in the first 50miles. And when it bumped, the speedometer did pick up for a second or so.

We did not realize that it would cause a big problem at first. We thought it simply was a speedo sensor failure, and would be an easy repair after back home. Since we got an GPS with speed readings, it would not cause too much trouble for us.

After around 50 miles driving, the bumps became worse and worse, especially when speed was below 50mph and when it was accelerating from stop. At one roundabout, the car was so bumpy like engine suddenly stopped working and resumed working and again and again that it almost got hit by another car joining roundabout. I thought it may not be safe to drive to Oxford any more, and we stopped the car and called for the roadside assistance (Aria assistance, coming with my car insurance policy) to come and look at it. They outsourced the job to a local garage. When the guy came 1.5hr after calling, he checked the volt of battery, and it was OK. He consulted the situation with his colleague in the garage that they concluded that it was simply a speedo sensor failure, and it was safe to drive back to Oxford. The bumpy was caused by the on board vehicle computer that it was confused by the inconsistency between speed and other readings. So the engine was not fed with proper amount of fuel sometimes. He said as long as the speed was kept high enough (>50mph), it would be OK. And there would be soon dual carriageway all the way to Oxford.

What he said did make sense. And the car seemed OK when speed was high. So we carried on our trip until it was on M5 just passed Essex when the car started to bump every 2 or 3 seconds no matter what speed. The check engine light turned on. Since each bump would cause a sudden deceleration, we could not maintain speed any more. It was very dangerous situation on a motorway. We had to pull on to the hard shoulder and call the assistance again for a recovery back to our home at Oxford.

Currently, the check engine light will keep on even when the engine is idle. The sound of engine sounds normal. But I can still feel the bumpy when I try to drive it from the road side to my driveway.

I am wondering what may cause the problem? Is the problem repairable? How much would I expect for the repairing cost? And if the consequent problems were caused by following the incorrect suggestions by the assistance staff, is the Aria Assistance liable for the cost of repairing?



Thanks!

Edited by ywy1234 on 13/06/2013 at 17:05