If your S Class is like mine (with the M119 engine) your oxygen will be located on the exhaust manifold, top side of exhaust, under the car before the cat. I only have one on my exhaust.

Did you mechanic read the codes from your engine? Depending on the mileage of your 93 500SEL, it might be time to change your O2 sensor. A poor performing O2 sensor can cost you $$ on gas milage.

If you decide to replace the O2 sensor, you'll need a 24mm box type socket for your s500. When I removed and replace the O2 sensor, the O2 sendor was a little tight, but after a few taps on the wrench with a hammer, it broke the seal and came out without difficult.

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Russell McMahon
Tulsa, OK
2001 CLK 320
1992 400se
1993 400e
2000 320ML