oil pressure pegged at 3 all the time - PeachParts Mercedes-Benz Forum

latitude500 · #1 06-11-2009, 05:31 PM

I have a 87 300sdl and as long as the key is in and on the on position or the engine is on. The oil gauge is always at 3. It doesn't matter what the car is doing or not doing. If I pull the key out and the power is turned off it will go to 0. Where is these pressure sending unit located on my car, and is it electrical or manual gauge?

I'm thinking that I have a grounding issue, but I wanted to check the the experts first.

Diesel911 · #2 06-11-2009, 08:12 PM

Here is the Russian Parts site, in English also:
http://www.detali.ru/cat/oem_mb0.asp?TP=1
Best guess; If your model uses a cartridge/canister Oil Filter the sending unit is most likely on the Oil Filter Housing somewhere.

Diesel911 · #3 06-11-2009, 08:16 PM

You might look here too. Not your chassie but they show a 603 Engine.

http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/18_4-1101a.pdf

http://www.ps2cho.net/downloads/MB%20CD/W124/Main.html

LUVMBDiesels · #4 06-11-2009, 08:28 PM

The gauge is electric like all W126s. The sender is near the bottom of the filter canister facing the firewall. You have to be under the car to get at it.

If you are going to replace it, do yourself a favor and drain the oil first.

Oh, in my case, the sender failed and pegged the gauge so I bet that is what happened to you too.

tbomachines · #5 06-11-2009, 10:16 PM

Seems like a stupid question, but did you let the car warm up fully before realizing this?

Jeremy5848 · #6 06-11-2009, 10:37 PM

In my '87 300D Turbo (W124, OM603), which has an engine almost identical to yours, the sender is in the ground leg of the oil pressure gauge. So, in addition to a bad sender (most likely cause), you could also have damaged insulation on the sender wire or a broken wire touching ground such that the gauge is grounded all of the time and therefore pegs the gauge. A much less likely cause is a short circuit somewhere in the instrument cluster.

To determine which possibility is right, disconnect the wire at the sender and see if the gauge stays at zero with the key on. If it still pegs, you have a short to ground somewhere in the wiring. If the gauge stays at zero with the key on and the sender disconnected, the sender is bad.

Let us know your results, please.

Jeremy

mplafleur · #7 06-12-2009, 12:02 AM

It's an open circuit to the gauge. Possibly a bad sensor, or wire connection.

Unplug the connector at the sensor and see if you get the same results. If you do, it's the sensor.

You can take an ohm meter and measure the resistance from the connector pin to the body (at the threads) of the sensor. It should read about 10 ohms.

The sensor was bad on my SDL when I put it all back together after my engine rebuild. I noticed when I turned the key to the on position that the gauged pegged at 3 bar right away. I diagnosed it was the sensor and verified that it read an open circuit. I took apart the sensor and found a broken wire inside.

Diesel911 · #8 06-12-2009, 01:08 AM

Quote:

Originally Posted by mplafleur

It's an open circuit to the gauge. Possibly a bad sensor, or wire connection.

Unplug the connector at the sensor and see if you get the same results. If you do, it's the sensor.

You can take an ohm meter and measure the resistance from the connector pin to the body (at the threads) of the sensor. It should read about 10 ohms.

The sensor was bad on my SDL when I put it all back together after my engine rebuild. I noticed when I turned the key to the on position that the gauged pegged at 3 bar right away. I diagnosed it was the sensor and verified that it read an open circuit. I took apart the sensor and found a broken wire inside.

At what temperature?

latitude500 · #9 06-12-2009, 12:19 PM

O yes, I've been driving it around all day like that. I scared me at first, but you get use to danger in my line of work. lol

Quote:

Originally Posted by tbomachines

Seems like a stupid question, but did you let the car warm up fully before realizing this?

compu_85 · #10 06-12-2009, 02:11 PM

You can reach the electrical connector on the pressure sensor easily from the top. As others noted the sender is at the bottom of the oil filter housing. It's a round can looking thing with a single wire coming off of it.

-Jason

mplafleur · #11 06-14-2009, 11:20 PM

Quote:

Originally Posted by Diesel911

At what temperature?

0 PSI (engine off) at any temperature.

latitude500 · #12 06-19-2009, 12:38 AM

Fixed:

Just wanted to say thank you to everyone that helped out. I tested the sensor and sure enough it was bad. So I ordered a new one from here for a total price of $37.32 shipped to my house. Change the oil and filter (amsoil) and swapped out the old sender for the new one. Works like a charm now. Pretty easy job, only took me 10 minutes to take off the old one and put the new one on. I did it from the top. Took me longer to change the oil. LOL

Thanks again everyone