As the title of this post states, my oil light is constantly on and I'd like to get it to come off. It came on the other day while I was driving with a bad waterpump. I was actually driving to relatives house to replace the waterpump and figured I would be able to make it since the pump just started to show signs of failure. Before I left I completely filled the coolant system up and took some spare water with me just in case.

Well, right before my exit, about 1/4 mile the oil light came on, since I was exiting the freeway anyway I was just going to pull over once I got off to check it out. The temp. reading on the engine wasn't anything to worry about so I didn't panic. Once I exited and slowed down enough the engine died and I coasted to a stop. I popped the hood and of course steam started to bellow out. I knew that I wouldn't be able to drive it so I had some one pick me up. I was parked in a no stopping zone but since they were about an hour away I let the engine cool down for the hour and tried to start the car, hoping that the didn't blow a head gasket or worse. Luckily the car started and I drove it 500ft. down the road to a parking lot. I had the car towed the following day.

Once at my relatives house I completed to work on the water pump, and changed the oil. When I started the car up everything was fine, ran good, no sign of overheated or any engine damage but the oil light was still on. So far it comes on every time I start the car and really don't know why.

I'm guessing that I might have damaged the sensor due to heat. The oil light in the dash is for oil temp, right?

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500

Check your manual. My '92 300E oil light comes on when the engine is one quart low on oil after the engine has warmed up. It has nothing to do with oil temp. There is a sensor on the side of the oil pan which monitors oil quantity. After the engine has warmed up, it sends a signal if there is a one quart deficit in oil quantity. I don't know how to tell if the sensor is bad.

I think on a 400E it's way more than a quart low that triggers the light - more like 2 or 3.

The sensor is probably ok. Try checking the oil and adding as necessary.

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Jim

I just changed the oil, it has the correct amount in the engine at the moment, but the light is still on

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500

Oil level switch S/43 is NC, so you have an open switch or a poor connection at the switch. It may just be unplugged.
Br/Bk , from X27 connector.
My first suspect is you jarred or unplugged the sensor wire connector , creating an NO circuit..which the dash reads as Low Oil..............

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A Dalton

I think Arthur is right on track here. (As always!)

I seem to recall the lower engine harness crumbling on my 400E shortly after I purchased it. I recall the symptom affected the oil level sensor or the oil pressure sender. I think it was the oil level... That was a long time ago!

My shop replaced the harness and took care of the problem.

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

Yeah, the sensor wires for that set-up come right off the main X27 plug .That is the one that goes behind the engine and feeds the starter solinoid circuit and such...it the one we use to jumper for NSS/K38 testing of starter activation ..[ or to steal your car ...]
The circuit is NC [ Normally Closed], so any OPEN [ as disconnect, broken wires , unplugged sensor, etc] triggers the lamp......pretty simple NC to ground circuit.

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A Dalton

Seems that is probably the case, a loose wire, or a bad wire due to the old wire harness failure. The only thing to go against that is that the light came on while driving, not right after working on the car.

Next time I'm under the car I'll take a look at the wiring to see if there's any issue, due to the mileage on the car (220k) anything could be an issue.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500