knowbenz

Well I've given you some things to check to verify because I can't do it from here. But aside from that, I have previously posted multiple incidents published by Mercedes Benz, I've done numerous M.E. replacements for this exact concern. I'd be willing to bet that almost all MB techs have done the same. The M.E. on those engines are full of known faults.

Go poke around on Instagram, there are dozens and dozens of techs there to ask as well

Simonas.st

OK, I will give one more try to go to dealership, and will post outcome.

metodiev

Friend hello! I made a registration in the forum because of your subject. I have exactly the same problem as yours.

Did you find any solution after so long?

This is my video and my problem
Simonas.st
friend did you manage to fix your problem?

Simonas.st

Hello,
not yet.
You see, I only use car very rarely, so it's not very urgent.
Local dealership told me the same, as guys in forum, that it's engine computer, probably. They also gave me number of the guy who is able to fix it for 300Eur. I called him, but he told me, that I have to leave the car for 3 days, which was not convenient for me at the moment. Now, when I've also bought w220, I will try that solution soon. Meaning in a month or two.

BTW, You have said, that Yours stops when You stop the engine. Mine, meanwhile run sometimes, even with doors and engine shut. The only way to turn it of is to lock the car. Than it runs for minute or so, and stops.

Keep me informed, when You solve it, and how.

metodiev

my fan works just like yours when you decide! When I turn the engine off, I turn on again when I decide. I was watching a video

You Tube

This is another model car, but with the same problem as far as I see it fixes the problem after changing the battery. We have two batteries and I wonder if I will not replace the batteries for the test. Although my car does not cause a low voltage problem.

Simonas.st

If it's a battery, it should be some kind of conspiracy to change engine computer instead.

Let me know if You swap battery and it works. I've tried to charge mine, didn't help.

metodiev

This guy has the same problem, but he does not solve the problem!

You Tube

It simply removes the pins that are responsible for the speed, but I do not think this is a solution to the problem. Because when it's hot and the air conditioner works, the system may need this fast speed to cool down! If there is any solution to me, I will write. Engine Control Module I guess should be patched, how do you think?

Simonas.st

I've never heard of removing pins to slow it down, but I will take time to take a look at it.

Could be ECM, but I'm very interested what happens when it comes bad. Since guy claims he could repair it. It means it is repairable problem. He's of course doesn't tell me how he's doing it.

Anyway, let me know about Your progress.

Simonas.st

Now I took time to look that video, and sorry, but for me it doesn't make any sense. What he's doing is proving, that signal to turn fan on is coming from ME. Where else should it come from? The reason, in my understanding could be not necessarily ME itself, but could be any related sensor, which sends wrong information to ME, which as consequence, turns fan on.

I hope someone with more understanding, like Knowbenz would jump in and clarify it.

knowbenz

I'm pretty sure I posted this before but the fan has four wires, main power and ground, a circuit 87 (power controlled by relay) power wire, and the signal wire. When the signal wire is just disconnected the fan defaults to max speed once it receives the circuit 87 signal when relay is activated by switching key on. The defective ME situation happens when the ME randomly activates the circuit 87 relay. All the fan thinks is that the key is on but it's not getting a signal from the ME. The signal for the fan to be in "off" position is a 10% duty cycle PWM signal from ME which is in the function description that I also posted above. If you have a volt meter that reads duty cycle you should be able to get a reading. If I have time I'll hook up a scope and get some recordings. Do all measurements by back pinning the connector, you won't get accurate readings by checking disconnected.

Also there is a bulletin posted by MB that if a fault code is resent (don't recall the code, something about temperature sensor or something) then you may need a software update. Out of a couple dozen defective MEs maybe one has been fixed with a software update in my experience.

My typical diagnostic strategy for fan issues is this. "Customer states fan on high speed when car is running"
Verify complaint
Check for fault codes, none found.
Check actual value for fan speed request. Values will give you fan speed request by ME, and fan speed request by ACC. For this example lets say fan request is 20% ME and 0% ACC. By these values fan should be on 20% and if I scope the signal line it will be 20% PWM signal.
If the fan is running on high speed I don't need to test power and ground on the big main wires.
Check the circuit 87 wire, confirm battery voltage.
Scope signal line. if I have a 20% PWM signal as the ME is requesting I can condemn the fan as it is receiving all proper signals yet it is defaulting to high speed.
90% of the time it will have straight battery voltage instead of a PWM signal. This will turn the fan on high speed. ME can be condemned.
Following these steps leads to accurate diagnosis in my experience. Others may have a different way to drag and thats fine.

If the fan is randomly activating when the car is off then back pin the circuit 87 wire on the fan, if your meter has MIN/MAX feature then turn it on and verify that you get voltage when the fan randomly activates.
If you do have power on the 87 wire then look at the diagram I posted previously, that was for an S class. Connector 2 Pin 27 on ME goes up to I1.9 at the front SAM, this is the ground side activation signal coming from the ME. If you back pin that you should read battery voltage when the car is off. set your meter to MIN/MAX and record the reading. If the fan activates and that drops to 0 volts then the ME is activating that relay, the fan sees the car on but no 10% "off" signal on the signal wire so the fan defaults to high speed.

I don't know if that answers your question, I feel like I was rambling thoughts down but I'm not about to reread it. Tools I us for these checks are Fluke88, Uscope from AESWave, and 4ch Pico scope if needed.

knowbenz

Removing the pin for the signal will do nothing but throw the fan to high speed. Fan defaults to high speed to avoid overheating if it doesn't get a signal.

That video is edited very poorly but I got at the end that he did change the ME and program it to the car which is usually the problem. Just saying the ME is turning the fan on high when the key is turned is vague at best. I want to know exactly what is happening which is where the scope readings come in. The ME is providing battery voltage instead of the 10% off signal that you should have on a cold start

knowbenz

Here are some images from a properly working fan and one where I bridged the circuit 87 wire to simulate ME turning relay on when car is off.

This is with the key off and the ME run on time has completed. Circuit 87 relay is NOT activated and ME is asleep. The meter is on the circuit 87 of the fan and the scope is on the signal wire. The ME grounds the signal wire so when the fan is not active it will read straight battery voltage.


This is the actual value screen showing 0% request and 10% on/off ratio which is "OFF", fan is not turning. Reading on scope is showing 9.8% which is inline with signal.


During the activation of the fan the reading on signal line can be seen to match the requested speed.



In this image I have bridged the circuit 87 relay providing voltage to the circuit 87 pin on the fan. Due to the fact that the relay has been activated (in this case by me but a defective ME in other cases) there is no 10% off signal on the signal wire so it remains at battery voltage and the fan runs on high speed


Same readings with the key switched to the on position. ME has activated the circuit 87 relay, the 10% off signal is on the signal wire and the fan is not running


Same readings with the engine running so now reading the charging voltage.



Hopefully seeing the readings will make more sense.

As seen in the actual value screen the request of fan being 0% means that there are no defective sensors that are making the fan come on high speed. If you have a coolant temp sensor reading way too high you will see the demand shown on this screen and you will see a reading on the scope to go along with the speed of fan. Have replaced many A/C pressure switches on other models but again, fan will only run with key on in that case and the request from ACC will be 100%.

knowbenz

Here is the description of the run-on time. If taking measurements with engine of as first pictured then be sure run-on time is over

Simonas.st

Thank You Knowbenz,

as far as I understand it is all to diagnose, that ME is faulty, and not anything else, right?

Do You know what is causing ME to fail? And how technically it fails?

Have You ever heard of ME repair with such a fault?

In my country people are very handy, and always trying to find solutions (maybe because of a habits from soviet past, when resources were not available), so computer technician from official dealership, explained me, that ME overheats, and therefore makes mistake. It should be burned some contacts inside, but it is possible to fix it. They of course not allowed to do that type of repair officially, but he has a friend who could do it.

How does that sound to You?

knowbenz

Correct, you can use these measurements to verify your vehicles problem. I'm not aware of what exactly fails in the ME to cause the random relay activations.

Simonas.st

Thanks, I will use Your explanation, and of course update, when I will progress with that.

Could You please, share some insight, regarding my other problem with engine check, and intermittent bogging sound from MAF? Thread lies here:
https://mbworld.org/forums/s-class-w...ear-again.html

knowbenz

I replied there but didn't see any fault codes so no clue whats wrong. I don't guess at what a car needs so could be anything at this point with the amount of info provided

metodiev

I am already a solution to the problem! Today I took my car from the workshop. I left her in a computer and electronics repair shop. They said this model suffered from computers. The problem with me was in the engine control module, the master said. I do not know exactly what he did, but I'm happy that my problem is eliminated! Simonas.st I advise you to fix the problem as soon as possible because the blade, when running at maximum speed, wears out very quickly and it is expensive. Separately, the battery and the charging alternator load, my battery already dropped below 12 volts and I dropped it to charger it once. Thanks for the wonderful theme. ! I guess there are many people with our problem!
This is the workshop that made the repair and I am satisfied!

Simonas.st

Good to hear, that You've solved Your problem. It is pity though, that You don't know what was the problem and how they have fixed it.

metodiev

I can not know, I'm not a master. I do not think any service will explain where the problem is, and explain that I will not understand it. The problem is that the problem is in the computer and there are masters who know how to fix it!
write when you develop on your problem.

ItalianJoe1

The problem is failed driver circuits inside the M/E, why are you so resistant to the repair? Knowbenz gave you incredibly detailed diagnostic steps and results, and you are still fixed on "but why does it go bad"

Just fix the problem and drive the car?

Simonas.st

First of all, I'm in no rush with it, I have more cars, and I only have to drive once a week.

Secondly, I don't trust local mechanics, so I like to know what is the problem, and how it will be repaired, before handing my car off to them.

Thirdly, I'm extremely curious person, and handyman myself, so I'm interested why things go wrong, and how to fix it.

Does that help You?

knowbenz

Had another fan issue come through that I figured I would post in here about since I already posted some pics regarding the issue.

This vehicle had the fan intermittently running at high speed. It would go on and off for sporadic amounts of time when it shouldn't. The car could be cold or warm, only with ignition on or engine running. With AC on or off it didn't matter.
So leaving the AC off I check values in ME that were showing fan speed requested was 10% which is "OFF". When the fan would randomly turn on the request remains at 10%. The fan would come on for average of 20 seconds at the time. On road test it would come on sometimes several minutes. Connecting the handheld one channel scope pictured above showed a 10% request when the fan was off. when the fan was coming on the displayed wave form didn't look how it should so hooked up the PicoScope to take a better look.


This image shows the fan working properly at 10% which is OFF. There is a measurement at the bottom showing 9.8% duty cycle.


This image shows when the fan comes on high. You can see the signal is not uniform and does not resemble a proper PWM signal. The fans maximum speed is at a signal of 90% and here you can see a measurement of 97.84% while ME request is 10%


**For example this is a proper 90% PWM signal when requesting a fan to come on maximum speed.**


Now in the following images you can see a bad signal that averages out around 50% request and the fan is running at half speed while ME is still only requesting 10%. The signal should be uniform and not varying the way it is here.



These signals appeared when tapping the ME with a screwdriver. When the fan is operating properly at the requested speed by ME, tapping the ME will result in a bad signal with a change in fan speed. You can basically turn the fan on and off by tapping the ME.

***All images in this post other than the example and the first image are known bad signals caused by a bad ME control unit. This is a different failure than the one discussed previously***

Minh

Hello @knowbenz , warm regards from Hanoi Vietnam. I'm highly appreciated for your contribution support on the fan issue of S550, you advice is high valuable for all of us.

I have friend of my with S550 4Matic 2007, he also struggling with maximum speed of the radiator fan (sometime the fan activated with maximum speed and it should not). We suspected that problem are related to AC, we did replacement many thing related to AC such as expansion valve, Condenser. Dryer accumulator but it could not help.

Do you think the ME control unit is the suspected one for this problem and the next action we need to try is to replace ME control unit?

Simonas.st

Hello Minh,

Before You replace the whole ME.

I just called one man who is able to fix that problem, and I asked how he does that? He told me that, he changes circuit boards inside ME. If he changes only one related to fan, than it's 150-170Eur, but he advices to change all, because later fuel pump usually fails, and that is 300Eur.

So I will drop my ME to him next week, and will see how it goes. I will also ask him to give me back defective part, so we all know what really is failing there.