After many years (and tens of thousands of HAPPY miles) the CEL on our (non-California spec) 1991 420SEL came on, stayed on, and then came back on the next time the car was started.

Starts OK, idles OK, runs OK... Light is on when running.

Car is at the Beach and approximately 180 miles from my most reliable and highly favored MB Indy shop. Don't especially wish to risk (?) the drive if by driving it that far I might exacerbate whatever problem there may be?

To my knowledge this car has never had the Oxygen Sensor (I do have a new one in my parts stash) replaced, certainly not in the last 15 years & 125K miles we have owned it.

I know this is not much to go on but any help or ideas as to a possible way to better diagnose would be much appreciated.

On the SC400 or the SVX I'd have some previous experience in coaxing a Code or two out of these pre-OBD systems: with the 420SEL I've had -0- problems so -0- experience. Don't even know if replacing the Oxygen Sensor would also clear the code if it actually fixed the problem... D(uh) U M B me!

Thanks in advance for any kind consideration!

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'91 420 SEL @ 199K, '92 SVX @ 181K, '93 SC400 @ 86K, '93 Kaw ZX-11 @ 30K, '87 F250 @ 181K , 2001 Valkyrie Interstate @ 6K, Y2K Honda NightHawk 250 with 1.5K, '88 420SEL I.@ 179K & the 2nd latest, an '88 420SEL II.@ 210K runnin' parts car, '85 F150 300/NP435