I have a repeat problem. Today check engine light came back upon a cold start.
The light came first time when I was driving in Cape Cod area two years ago and called a local dealership where I was told to open and properly close the fuel tank cap. This helped for a week or so.
My dealership (North Toronto Mitsubishi) attempted to troubleshoot this problem. The mileage was 35 K at that time.
I needed to come back 4 (!) times with the light going off before they were finally able to fix that (every time the onboard computer was reset).
It was the catalytic converter, 3 other times they replaced oxygen sensors.
Apparently the technicians did not have the adequate training. I was told to use premium grade gas (always used it). 2-3 months ago my SUV gave me vibration at 1500 RPM especially when driving uphill, now gone (not sure if that helps), I decided to use fuel additive and the vibration gone. The dealership found nothing abnormal.
Last night I did a quick relocation of the truck (cold) from one spot on the driveway to another, the temperatures dropped overnight when I started my truck this morning
the check engine light came back instantly. I turned the engine off and on, but the light still on. I have not noticed any difference in how the vehicle drives, nor noises.
I called the dealership and they told me to see if the light will go away in a few days, if not to come back to them, I will post an update on my story.