A strange problem because its not usual to want the MIL to come on but ........ Most of the time do not see the lamp lit even when first switching on the ignition, then stays off. More infrequently the light is showing when ignition is switched on but stays on for that journey. Possible connection fault but where do you start looking? Thanks

You will need to get a code reader (or get the codes read) to see what is causing the light to come on. Even with an intermittent fault the code should be stored enabling you to have a start point to sorting the issue.

Thanks, yes a code reader a must have because of non functional MIL. Garage identified EGR fault whilst MIL working