King320

So i was driving this weekend and my engine fan kicks over onto high and sounds like a jet engine or tornado siren. Funny thing is the car is a lot more responsive and louder, but I'm worried it might burn up the fan if it goes on for too long.

Tech says its likely a relay switch thats stuck. Any ideas on a DIY fix? Would disconnecting the battery reset the computers?

clemson_tiger

Good question! My fan (fans? not sure) sound like they run on high all the time and you can hear them coming more than you hear the exhaust! LOL I know they are not "stuck" because when I crank the car they don't jump on, but they seem to run on that crazy high speed way to often. I'm looking forward to hearing responses to this thread.

loudandheard

I had a neighbor that this happened to, but the thing was that it occurred while the car was off. Turns out that he did not have the lid on his fuse box in the engine bay and the fuses were getting wet.

If this occurred after rain or washing your car, I would say check your fuse box. Every thing went back to normal after his fuse box dried and we did end up replacing some fuses, but it was related to his car not starting.

Hopefully this give you an idea.

King320

Did happen in the rain now that you mention it. I may just drive it for a few days. Was it the trunk fuse box or the one by the driver's door?

Also, the car gave me a battery undercharged warning and told me to turn off accessories that were consuming electricity. I just drove it really hard for a few miles instead and the warning went away.

loudandheard

You actually have a fuse box in the engine bay. If you are looking at the engine bay with the driver side to your right, the fuse box is right in front of the driver's side by the back of the engine bay behind a panel and a lid. Hopefully that helps. You need to make sure it's tightly covered, my neighbor did not have any covers on his fuse box and it rained hard. The fan came on with the car off, so he had some issues. Luckily the fuse box dried out and all we had to do was replace a few fuses.

There are 3 fuse box locations. One in the engine bay, one in the dash by the door, and one in the trunk, all of them on the driver's side. Hope that help.

King320

Yep, i know the location you are referencing. Thats where the ECU is as well, correct? I'll drive it for a few days to see if it dries out and if not i'll take it in to get it checked out.

ruben65

When I start My C55 and have the A/C on, the fan kicks on at high speed, but only when its HOT outside (Like Arizona 90+ degrees hot)... after a few minutes it settles down and is normal, unless imin stopped traffic.

If the A/C is off it will only run if the engine gets hot enough to warrant it at high speed while driving or stopped in traffic.

I asked a few Senior Mercedes Tech's that im friends with at 2 dealerships, (1 tech owns the same car C55) and they said on the C55 that is normal if the A/C is on, or extreme temperatures when stopped.

1. To make that high pitch whine (jet like) when A/C is on. (usually on start up or sitting in stopped traffic)
2. It also does that when you start and its hot outside the oil pressure is high and something else... and it tries to reduce the pressure and cool it off.

In the winter time I do not have either issue, only when it starts getting over 90+ degrees here in Arizona.

King320

I've had it in the shop since Thursday. Thankfully my mechanic is doing this under warranty since they replaced the fan less than a year ago. They have been working on it for 3 days straight and still cant figure it out other than knowing that it must be a shorted wire.

The car still kicks the fan on full blast after sitting inside and with the engine off for 24 hours, so this is not a "normal" fuction. Everything with the computers is fine (they took it through MB's 50 step computer systems check and it passed everything), so its just down to going through looking for a loose ground or shorted wire.

VERY glad I'm not having to pay for this.

AMGC43C55

your engine control unit took a dump.

King320

No, ECU is fine according to every test run. Its a short somewhere in the wiring harness they think.

King320

3 fans and a week of work later and i still sound like i'm taxiing down the runway...

Got it back for the weekend, going to take it in again on Monday. It would be much easiser to just get a new wiring harness, dealer quoted $1200, anyone have a suggestion where they could be found cheaper?

Waldo_uk

Hi everyone. I know this is an old thread but I had this same problem with my 03 w211 recently. All the dealers saw were £ signs. Even the indys seemed flummoxed and had never heard of this what seems to be a common fault. The solution for me was refilling the washer wiper reservoir! I kid you not! Apparently the washwiper reservoir and engine coolant warning sender switches are wired in series and my engine thought I had low coolant so was doing what it should and put the fan on full speed to keep my engine from overheating in case I had low or no coolant.

I allowed the wash wiper levels to drop and the same problem didn't occur everytime but for the first time, the wash wiper fluid low warning came up. If you have this problem then just check your wash wiper fluid levels and top it up. Turn engine off, allow the computer to recheck everything when turning on engine and hopefully, the solution is that simple and cost effective.