Mercedes benz S 320 model 140 from 1992

Question edited for a lot more clarity.
Question moved to model category.

These things have fuses boxes all over the place and are a nightmare to work on :>D

Fuse Box Diagram Mercedes-Benz M-Class (W164; 2006 ...

https://fuse-box.info > mercedes-benz > mercedes-benz-...

Here you will find fuse box diagrams of Mercedes-Benz ML280, ML300, ML320, ML350, ML420, ML450, ML500, ML550, ML63 2006, 2007, 2008, 2009, 2010 and 2011, ...

Fuses W164 M-Class 2006-2011 Diagram, Box Location ...

https://www.mercedesmedic.com > fuse-box-location-d...

Fuse locations on Mercedes-Benz M-Class W164 2006-2011. Main fuse box and relay box is located in the engine compartment. Rear, passenger side in the trunk.
Model: ML 320 CDI ML 320 BLUETEC ML 350 ...
Years: 2006 2007 2008 2009 2010 2011
Chassis: 164
Make: Mercedes-Benz

Fuses W164 M-Class 2006-2011 Diagram, Box Location ...

https://mbworld.org > attachments > m-class-w164
PDF
Fuse locations on Mercedes-Benz M-Class W164 2006-2011. Main fuse box and relay box is located in the engine compartment. Rear, passenger side in the trunk.
9 pages

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Check you brake stop switch located behind the brake pedal

code p0400 refers to exhaust gas recirculation(EGR) system---flow malfunction.===causes---hose leak/blockage--basic setting not carried out (if applicable)---wiring---EGR valve ---EGR solenoid---ECM
check out the valve and solenoid.

You cannot accuratly check the freon level without compressor engaged. Without car running that needle better be pegged or its low. Charge with car running with dials set to max cool with fan speed on hi. Slowly while charging with compressor engaged bring it up to 2K rppms while filling. Should take around 3 cans. Get the stuff with stop leak.

it is the brake switch, behind the brake pedal.

You have a simple plunger switch on the brake pedal. This can be lubricated or replaced. Simple job.

Check the pole/cord going to your gas pedel..u may have to take up the carpet.. but it could be a bearing in the pedel..

The Symptoms tell me it is a head gasket. A leaky or bad head gasket would cause all of the problems that you mentioned.

Burning water causes White Smoke, Burning Oil causes Black Smoke. The oil and water are mixing with the gas in the cylinders and causing it to run bad. Pull out the dipstick and look at the oil on it. Does it look like good oil? Or does it look watery and or foamy or grey colored. Open up the radiator and look inside, do you see oil?

This seems almost text book to me... I would have someone local to you to have a look at it to be sure.

too much fuel--- try cleaning the air filter first if this doesnt work then its a sensor problem and i suggest taking it to the dealer as if your not sure what sensor it is then it can be costly changing a perfectly good sensor .