How many O2 sensor(s) are on the 1993 400SEL (W140)?
 

How many O2 sensor are on the 1993 400SEL (W140)? Is it a DIY job??? If so, does anyone have detailed instructions? Pictures would be helpful. :cool: My direct email address is: wkr21@hotmail.com THANKS-A-MILLION!!!

ONE (1) sensor & yes an easy DIYer.

I always wonder why almost all modern V8/V6 engines start to use 2 upstream O2 sensors, 1 per cylinder bank, plus at least 1 downstream O2 sensor, that's more than MB M119's single O2 sensor.

My 11 year old 400E just passed emission test last week, the maximum pollution I got for idle and 40kmph was HC of 40 ppm and CO of 0.03%, does anybody know what numbers one normally gets from new V8 MBs?

Thanks M.B.DOC!!! Do you have detailed instructions??? Are there any special tools required??? Typically, how long should it take? Do you have any illustrations, pictures or links???

Thanking you in advance.

BigBody400SEL

The upstream O2's on each bank monitor combustion efficiency, thus control fuel trim on each bank, because on MPI, SFI and others, each bank has its own fuel delivery system.

The downstream O2's monitor catalyst efficiency, all for the sake of cleaner exhaust.