Engine Warning Light & Limp Mode at 60mph
 

Hi. I have a 2002 Diesel PT Cruiser. As soon as I reach 60mph the engine warning light comes on and the car goes into 'limp mode', losing about 30% power immediately, getting slower the longer I continue to drive. If I pull over and restart the engine, the light goes out and the power starts to return (until I hit 60mph again).

As long as I don't have to go at any speed, such as around town, the car is fine. As soon as I have to do a longer journey I know it's going to be a nightmare!

I've taken it to a garage and they can't find anything wrong and have checked the turbo which they say is fine.

The only other symptom is a lot of black smoke when I accelerate in third gear.

Please can anyone help! Thank you :-)

Oh, the error codes are: P0403 and P1685