Approx 4 months ago the Engine Management light came on. My usual service garage changed the air filter and all was well for a short period. A new "compatible sensor was installed. The light, not much later, came on--a replacement compatible sensor was installed--this too came on. I then needed an MOT which failed on "emissions". A genuine Mazda sensor was installed. The car passed the MOT. The light came back on. I had it checked on a diagnostics machine--the light went of for 2 miles then came on again. My garage had the car for an entire day but was unable to give me an answer from the diagnostic tests. They are now going to use an oscilloscope to try and reach a conclusion. So far there seems to be no particular reason for the light being on. Anyone with any ideas. I'm really puzzled and frustrated.