knowbenz

This is the wiring diagram for the fan. M4/7 is the actual fan. In the diagram it shows pin 2 is the big red wire that has 12v at all times.

Pin 1 is the big brown wire that is grounded, this should have 0 ohms to ground.

Pin 3 is the circuit 87 input to the fan, this will have 12v with the key in position 2 and engine running. It is controlled by the circuit 87 relay.

Pin 4 is the actual signal wire coming directly from the M.E. This is where the fan receives the request from and at what speed to run.

Hopefully this will help to diagnose the problem. That part you posted looks like a front SAM which doesn't exactly control the fan

If you had no power on that green and red wire to pin 3 it also supplies power to the purge valve Y58/1 and the charcoal canister shut off valve Y58/4, you would likely have fault codes set relating to those components or system

Simonas.st

You made a tremendous job here. I suppose it's very handful, when You have star diagnostics. I don't have one. Dealership has, but they are quite stupid, and don't even know english. Is there anything I can do with multimeter, or should I go again to dealership?
I'm very pissed off, when I pay for hour, and they don't find anything.

OR, maybe the best is to spend 79eur+10eur shipping and try control module from ebay in Germany?

knowbenz

You can test for the main power and ground as well as the circuit 87 when the key is on. you won't be able to get a PWM reading on your meter since it is too slow to capture it. You will only get an averaged reading which can still be useful. It's really hard to say without proper drag equipment. Where are you located? The M.E. is coded to the vehicle so if you get a used one you would have to have it unlocked and then reprogramed.

Simonas.st

I'm in Lithuania.
I'll try what You've written here.
I'm not talking about buying used M.E. , which, I believe is engine computer.
I'm talking about fan control module, please take a look at ebay link above.

knowbenz

What you posted looks like a front SAM.

Simonas.st

So it has nothing to do with my case?

knowbenz

I can't see how

Simonas.st

Hello again,
some update:
Found a guy with Star from local MB forum, and he spent some time today trying to find out the cause. What we have/ haven't found:
1. Fan control unit reacting to actuator command, and increase/ decreases fan speed as told.
2. Interior heating unit requires 75% of fan, which is odd, and it has 54C itself. So that was a suspicion, but when climate control was turned of, star has showed, that demand is 0%, but fan still was running fast.
3. When engine coolant temperature was 92C, and fan was blowing like hell, temperature was not dropping. Possible sticking thermostat? But if so, why fan kicks in, when I open the door?

That's the news so far. Does that tell anything?
Thanks.

knowbenz

Jeez you're still working on this??? Put a scope on it. Or just get a new ME. I know you hope something else is wrong with it. Test is simple, do it.

Simonas.st

I'm not "working" on it. I'm using car once a week for 50km, so it's not a big deal, but it has to be solved eventually.
I don't know what is scope, don't have one, and I don't know where to borrow. Doesn't STAR has this capability?
Just throwing in new ECM sounds very easy, but it's not the cheapest try. Will You refund me, if that will not solve the problem?

knowbenz

Refer to the previous pictures I posted. There is only one control wire to the fan, it comes from the M.E.

ecmexchange

The only possible answer must be gremlins. On a serious note, once the problem is nailed down, you are gonna love the feeling of not worrying about it and just enjoying the car.

Simonas.st

Hello again,
I'm still "working" on that. Wasn't able to get a scope, but have some clues.
In winter time fan turned on only occasionally, and only for driving for a while.
Now when weather is 20+ C, it starts immediately when I unlock the car in the morning. So it's not simply short somewhere, it reacts to temperature change.
Also I've found the way to keep it running all the time on high: after driving I turn on auxiliary heating/cooling (in the middle of dashboard), close the door, lock the car, and fan keeps running on high as long as auxiliary heating/cooling is on.
I'm very grateful for everyone who gives me clues. I know I could leave the car in dealership until it's solved, but I'm very curious. I like to find out what is causing the problem.

becosemsaida

Since you have referred that it comes on with the climate control / AC unit check that unit too. Maybe that is the culprit....... If you check KnowBenz's schematic you could do the test easily. No scope needed just a 20€ multi-meter in the DC position (black on chassis or ground of the starter battery). Opening the door will get the car out of "sleep" and if the signal is permanent it will start the fan.

The fan comes only up on two occasions: heat of the engine, check the valve on the engine (somebody will tell you where) and when you activate the AC unit....... Of course this is all managed by the ECU but just to check that there is no rogue signal coming in start checking this. At least your fan is working.

Hope you can solve this,

Beco

Simonas.st

Hello, and thanks for Your response.
Now I've checked wires coming to the fan in two situations:
1. Car not running fan has stopped running.
Big red wire: 12V
Big brown: 0V
Red/green: 0V
Brown/red: 3.5V, or 0V, not sure

2. Car is not running, but auxiliary heating/cooling turned on.
Big red wire: 12V
Big brown: 0V
Red/green: 12V
Brown/red: 3.5V

So why auxiliary heating/cooling could possibly trigger the fan?

knowbenz

The red/green is 12V with key on. The fan speed is controlled by a PWM signal from the M.E. I feel like I have typed this numerous times by now. You aren't going to get a proper reading of a PWM signal using a cheap meter. With all the time you have in this why haven't you had a professional diagnose the issue?

Simonas.st

Negative. I've just done measuring again. Key is in my pocket in both situations:

1. Car not running fan has stopped running.
Big red wire: 12V
Big brown: 0V
Red/green: 0V
Brown/red: 0V

2. Car is not running, but auxiliary heating/cooling turned on.
Big red wire: 12V
Big brown: 0V
Red/green: 12V
Brown/red: 3.5V

I agree, that it's ME sending signal to rev up the fan, but the question is why? And I know it's not simply mad, because it has pattern.

I understand Your frustration, please understand mine. Official MB dealership found nothing, suggested to change battery. Done it, no changes. Later found local mb forum member with recommendations, his assumptions is posted up this thread.

Thanks You for Your patience and time.

becosemsaida

So now you have found the culprit with measurements done according to the schematic provided by Knowbenz, so next step is to change the aux heating module. I don't use mine (it has error 9000 on it, seems to be special since there is NO reference anywhere). If you don't need it and if you want to cut corners you can always figure out what the wire is that's triggering and cut it..... Not my kind of solution but it seems that you want to do this on your own.

Still just to be sure and to solve this permanent i would take it to a good indy or an MB specialist/dealer...... Once solved all is new, just my thinking of course.

Beco

Simonas.st

Yes, and no. Problem is that sometimes fan turning high, even if auxiliary cooling/heating in not turned on, and even if turn of climate control, it doesn't stop spinning fast. Or is there any latency?

knowbenz

I forgot you were in Lithuania, here in the US, M.E. gets replaced for this very same issue on a regular basis. Here are more diagrams. For all the different options below "U484" is for an S550 with a 273 engine. You will see circuit 30 is power all the time, circuit 31 is ground, circuit 87 is power controlled by relay, and pin 4 is the signal wire. circuit 87 comes through a Z splice labeled Z7/5. On the next diagram you can see it comes from connector I2 pin 3 on front SAM which is from fuse 23. Follow that back and you can see fuses 21-24 all get power supplied from relay kC in front SAM. You can see on the diagram that the signal for the relay to activate is coming from pin p on connector I1 at front SAM. That wire goes directly to the M.E. control unit and nothing else. as you can see on the diagnostic chart these are activated with ignition on.

knowbenz

Here is a diagram related to function description of the fan control. The illustration is of a 272 engine in a 171 chassis but is the same for all cars with 272/273 engine. Anything you do to wake up the CAN network will potentially activate the fan with a defective M.E. control module.

Simonas.st

From the last diagram, I understand, that any of the components, if faulty, could trigger the fan. How You conclude, that it's ME faulty itself?

becosemsaida

Well, i wasn't too far of with my assumptions........ So if you want to check if it's really the ME you have to check all that is involved according to the (great) work done by knowbenz.

But let me quote you from his post: "If the actuation is faulty the electric fan rotates with max. speed" and "Status of the AC is determined through the instrument cluster via CAN and the coolant temperature"

Take it to the dealer, it will cost you some € but you will have it sorted out. See it as a lesson that you learn about your car. The time and the possible damage you make to your car is NOT worth it.

Beco

Simonas.st

You are not following, my friend, dealer is not able to diagnose, let alone to repair.

becosemsaida