So I have this small OIL LEAK for a while now and no one really knows where its coming from but now the OIL LIGHT is coming on but goes off. I check the OIL level all the time and its fine, I also check the OIL PRESSURE and thats fine as well. It now seems that the OIL LIGHT stays on when doing highway speeds but seems to go away when im driving around the city with stop and go. I think the mysterious oil leak is leaking on that oil sensor(wherever that is). Thoughts? Also, where is the ENGINE OIL sensor exactly located. BTW, the oil leak is coming from the front/side passenger side of the engine, i thought it was the OIL filter housing but thats seems to be OK

there are two oil sensors. One is for oil pressure and another one for oil level. Oil gauge has also a red light at its bottom and taht light should come on only if the pressure is critically low. But I studied some topics about it and I found out that that red light will come on also if there is open circuit on wires or on the sensor itself. And in my case it was so: I replaced lower engine wire harness and everything was ok.

I am not sure to which oil light do you refer. If it is the square red light in the row (it is for oil level) then I do not have any idea, but maybe it functions in a similar manner as I described for oil pressure light. This would be logical because if wires between the oil level sensor fail or if sensor itself fails, then the driver should know new sitauation. I think only an expert who really knows how the thing works can tell you an answer. But you cannot lose anything if you search for bad wires.

 

its the yellow light right by the coolant light, not red

 

Thats your low oil indicator, that light will come on when the engine oil is low but will go off after a short time, just enough to let you know its low. Then will return on and off until you top it off. That sensor is a thru block mounted connection. The actual sensor is located in the pan connected to the oil pick up unit. on the passenger side of the block there will be a small single prong plug mounted in thru the block just above the mid-pan/block mating surface. thats the plug for the sensor. Check to make sure the connection/wiring is ok. If it is ok then the sensor itself may have failed.

 

so in order to change the sensor, the pan needs to be removed? Any pics of its location

 

Im looking into some of the pictures i have of other builds, Im not sure if you could get to it by removing the inspection pan or not. Im sure you could get the sensor out but the wire thru the block is in question. I just had apart a 500sel for head gaskets, you probably saw the thread. let me do some checkin and i will post shortly for you.

 

Now this is not the exact picture of your motor, But the concept is the same. Its located on the pass side as this diagram is showing the drivers side for this engine. You will be able to replace the sensor by pulling the inspection pan down. The plug through the block is held on by a clip that looks like a clip used to hold a brake line in its holder. When you replace it clean the hole well, This will ensure no leaks . when you replace the inspection pan make sure you torque to spec so you dont bend the pan and create leaks. Torque is to be set to 9nm . Then you should be all good.

Part labeled s43 is the sensor,
#2 shows the body f the connector
#4 shows the o-ring

 

In this post from the Mercedes Mechanix, Dutch has a couple of pics of the sensor itself, but not of where it connects through the block. I have taken the liberty of annotating one of his pics for clarity.

http://www.benzworld.org/forums/w140-s-class/1339994-s-klasse-119-97-engine-v8.html#post2604132

 

Very nice! i looked in my pictures and i couldnt find one that clear. That should help him out alot!

Way to double team!!!!!!

 

I had the the Oil light on as well just like you ,Oil level was perfect and Temp as well, the MB mechanic told me that it is a common Fault that those Oil sensors stop to function ,you dont need to remove the oilpan ,unless you have a real Problem within your Oilpan's sensors ,start with this one ,takes about 15 minutes to change the sensor,thats with jacking the Car up & remove/Reefit new ,some oil will poor out when u remove it just a few drops ,sometimes on highway speeds if a yellow light comes on ,double check it ,as i mistake the oil sensor (when i 1st bought mine ) for the coolant sensor ,just addet a little water & all was good.
Location is underneath the Oil filter down the Bottom ,that is the Yellow light i had on , after i changed it all was good again ,i'm probably using the wrong Name ( Oilpress /Oiltemp Sensor ? ) .
Your little Oil leak by my experience comes from that Switch/Sensor, if the drop of oil is at that Location under your Car .:thumbsup:

 

Low Oil Level Indicator Light

The engine oil levels in the oil level sensor (S43) and in the oil sump are balanced through the bore (c).
The bore (c) is opened or closed by a bimetal snap plate (8). The bimetal snap plate (8) opens from an engine oil temperature of 60 - 70 °C and closes at an engine oil temperature of 30 - 40 °C .
When the engine oil is changed, the oil level sensor (S43) is therefore filled through the vent bore (d).

The oil level is measured with a float (6) with ring magnet (7) and a contact (arrow). The contact (arrow) is closed by the magnetic field of the ring magnet (7) depending on the position of the float (6). The contact (arrow) is open when engine oil level is less than "min", and closed when engine oil level is greater than "min". When contact (7) is closed, vehicle ground exists at the base plate in the instrument cluster and the indicator lamp (e.g. model 202: A1e12) does not come on


One diagram shows the sensor when full, other shows when low


I believe by the symptoms he is having this is the potential problem verses the oil sending unit. both sensors control totally diff functions.

 

I just had my oil and filter changed on 96 s500 coupe. Now the oil level light comes on. I checked oil level with dipstick and it is ok. What went wrong? This light never came on before. What is the cost of the repair at MB dealer that I should expect?

 

Don't go to a Dealer or service station just to change that sensor ,you do this type of repair yourself including oil & filter changes , even spark plugs if you have a little idea of how to handle a spanner , if you do ,then there is no need to spend extra money to someone (like it has just shown for you ) to make your car defective or get it back with a defect ,it's very common with our W140's in general .
Here is the Sender you need>> Mercedes R129 W140 URO Sender Unit With 2-Pin Connectors 0095420817 | eBay << , you probably find it even cheaper by a couple of bucks ,not worst the effort .

Organize a little bucket (size of a Coca Cola can but wider) where some oil can drip into when you remove that sensor ,oil will come out then stop, park the car on a level surface or between a road & high Kerb so you can slip under it ,no need for a jack this way . Unscrew the sensor , screw new one in & it's done , make sure you get a new Copper O ring otherwise it will probably leak drops of oil , easiest repair on the W140 M119's & M120's .
You can even change that sensor from the top if you have long arms & a little patienz,all you need to remove is the air intake hose on the side of the sensor ,Location is directly underneath the oil filter with a twin wire to it .

Alternatively , buy the Sensor and go back to the guy that changed the oil , he should do it for free to you since he was the cause , you just being nice buying the sensor ,soo ... you know what I mean ,just be CAREFUL they don't brake something else in the process like these mechanics always seam to do ,fix one thing - get paid but brake another thing to get paid even more ,that's way no Mechanic touches my car ,been there done that never again.:thumpsup:

 

Has your lower harness been changed? The oil level sensor is inside the lower oil pan. As I recall, the sensor is about $50. No clue what a dealer or indy would charge to replace it. I did my own.

 

Chris, it is not about oil pressure sensor, it is about oil level sensor, is that right? to replace the latter one must remove oil sump.

 

Absolutely Samo ,thanks for the correction, still good useful info ,lol .
Removing the oil pan is not that bad once that Bar underneath the oil pan is slight lowered , just make sure the oil has been drained into a new plastic bucket or something .
Once the Pan is of , that sensor is on the side there ,
you would need some hex tools to remove it .
I have a sensor here ,doesn't look like a part that is difficult to remove , I would say the hardest part is the removal of the pan with all those Nuts around it .:thumbsup:

 

to remove oil pan:

raise front end of the car securely. use hand brake, etc.
unscrew left and right pair of bolts of engine mount from below. remove plastic protection around engine fan.
use hydraulic jack and a wooden block for instance to raise the engine for several centimerers. Jack is on the floor.
unscrew bolts on the oil pan. remove it. use new gasket, be careful when install, it is very easy to break it especially if the oil pan is not flat near bolt holes. flatten it.

this was the hardest job in my life, do not laugh. I think I spent several hundreds of euros only on gaskets. + new pan ... etc. Several attempts (i am not telling how many ...). Most idiotic design I have ever seen in any car, socialistic ones included in statistics !

 

I have a w203 272 engine. I’ve been struggling with the “check engine oil…” for the past two days. Today I went to replace both my oil and oil filter hoping the message will disappear, it did not. I poured 8L of oil and still the message still appear. Please help me with ideas😭