Mechanics

AUXILLARY FANS

1995 Mercedes Benz 300d

Electrical problem
1995 Mercedes Benz 300d 6 cyl Two Wheel Drive Automatic

the auxillary fans come on whenever the ignition is switched on even without or with the engine running.
Avatar
Cairo
April 6, 2009.




Hello
Thanks for the donation

Suspect faulty cooling fan relay. Replace relay with known good relay to see if solves problem. If not, inspect engine coolant temperature sensor.

Thanks for using 2CarPros. Com!

I have already replaced the old relay with a new one and there was no change. Is the engine coolant temperature sensor blue and located on the top front of the engine where the radiator hose enters the block? If so, is there a way to check it without replacing it?
AD

Tiny
Cairo
Apr 6, 2009.
I have already replaced the old relay with a new one and there was no change. Is the engine coolant temperature sensor blue and located on the top front of the engine where the radiator hose enters the block? If so is there a way to check it before replacing it?

Tiny
Cairo
Apr 6, 2009.
It is located at center, upper engine area, mounted in rear of intake manifold. Best way to check is to use a scanner that shows what the sensor is doing. It is much cheaper just to replace the sensor. First inspect wiring to the sensor to ensure it is not damaged.

Thanks for using 2CarPros. Com!

I looked on the underside of the intake manifold.
What I see is not the same as a picture of a coolant temperature sensor that I get on the internet. What I see are 2 electrical plugs plugged into a part mounted on the manaifold with vaccum lines attached. Is there a picture for me to look at?
If you can't provide a picture where can I look for one?

Tiny
Cairo
Apr 7, 2009.
You may be looking at the MAP sensor...below is an example picture of what the sensor will look similar to


http://www.2carpros.com/forum/automotive_pictures/261618_1_33.jpg



Thanks for using 2CarPros.com!

On the block toward the rear on the left side I find a part that is blueish in color with a wire plugged in. Your picture doesn't match any of the parts picture that I have pulled up. Could we be confusing diesel and gas engine parts?

Tiny
Cairo
Apr 7, 2009.
Your vehicle is gasoline correct? I have not searched for any diesel parts.

When I logged on I entered that this vehicle is a 1995 E300D meaning diesel. Please advise if you need additional information.

Tiny
Cairo
Apr 7, 2009.
Sorry about that. I can not find a picture of the Diesel ECT sensor but I have dug up some wiring diagrams. First of all, I would like to bring to your attention that you have 2 relays for the auxilliary fan. Did you test both of these relays? Next, it appears the ECT sensor has a brown/yellow wire and a blue/yellow wire to it. Perhaps this will help you determine the correct sensor. Once you find the sensor, ohm it while the engine is at operating temperature. It should be reading 300 - 400 ohms. If it is higher or lower than sensor needs replaced.


AD