I have had the Cat warning light lit on my dash for the last few weeks and told it may be the Maf Sensor.. Would the light stay on even if there was no fault.

As i have just replaced my Kenwood stereo with the Origional vectra ( as i`m selling car) , and when i put the Radio in and Turned engine on it went out and has still not returned after 200 miles..

Is this possible , Has anyone any ideas