M273 Check Oil Level

[jteez]

Hi All,
I've searched and haven't found anything so would be greatful for any input.
Basically I've had my 2006 SL500 for almost 2 years now and been great.
I've started getting a 'check oil level' message in blue on the dash but level is good (at max) on the dipstick whenever I check...
Do these sensors go bad? is it actually a level sensor or pressure sensor...
I've got 6K left until next service...

Any thoughts?
Thanks