kmakiifl

I reside in US. Shortly after getting my used clk, I accidentally used 89 octane in lieu of premium, the check engine light came on. I checked fuel tank cover - not the issue. The mechanic said it was the catalytic converter, muffler shop changed pre-catalytic to straight pipe in that section - not the issue as computer was re-set, light went away overnight but came back.

Any other possibilities to check?

Thanks.

Untertürkheim

The check engine light should have a code that will say exactly what the problem is. Go to a dealer and they will fix the problem correctly.

Ausmbtech

Check what code it is to find what area the problem is in.

As for replacing the pre-cat with a straight pipe...........bad move. Now you will definately get the engine light because the o2 sensors with recognise the cat as being inoperative (missing)