On some cars the "check engine" comes on every so many miles whether there's a problem or not. Check around for that (owners manual or a repair manual) On my old Audis the oxygen sensor light comes on at every 30K miles. I know where the reset button is, so if the car is running ok, I just hit the reset button and ignore it.

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)