I recently bought an 04 mazda 6 from a private seller the car starts and runs great a little sluggish upon acceleration from a stop but otherwise a very well running car. About 50 miles down the road CEL illuminates.I take it to be looked at and the EVAP system isn't ready and has a pending catalytic code.the mechanic was dead set it was just leaks.so we smoked it and repaired the leaks.I took it to be inspected because I'm only on a 10 day and it failed emissions for evap and the pending cat code the mechanic said it just needed to be driven more so I did so and low and behold 30 miles in that lovely CEL is back on.This is becoming an issue and I'm running out of time any idea as to what I should try next.
My car has 126000 miles.
My car has an automatic transmission.
It is possible that you could be experiencing a catalytic converter failure. This can be due to the fact that after driving 30-50 miles the exhaust system heats up quite a bit. Once the exhaust is heated up the catalytic converter begins to show signs of failure. Often times when the precious metals inside the catalytic converter fail, they melt together as if they have been welded. This makes the orphice through the catalytic converter much smaller and increases the backpressure of the exhaust. This will prevent the engine from breathing properly. I would recommend having your catalytic converter inspected and replaced as necessary to resolve this issue.