W204 Engine fan turns on with engine off! Help!

[ashtonhill]

Hi there,

I have recently made the jump to Mercedes after a long line of BMW's and all was well until an anti theft display popped up on the screen and wouldn't let me start the car. After not being able to work out what was wrong, I disconnected the negative terminal on the battery for a few minutes and then re-connected it. This solved the problem and the car starts and drives fine now.

The problem now is since reconnecting the battery, the engine fan turns itself on about 1 minute after the car has been switched off and the key taken out. The fan quickly picks up speed to the extent that it is exceptionally noisy and will not stop unless the ignition is turned on.

Does anyone have any ideas whats wrong and how to fix it?

I have had to disconnect the fan and so am not happy driving it really. The only other thing to mention is that the car had been sat for about a month previous but had been started up and shut down again quite a few times when shunting it around on the drive. I wonder whether its damaged the battery? When I check voltage between the two terminals it was roughly 12.5v

Any help much appreciated - first foray into Mercedes not going so well at the moment....

 

[optimusprime]

Check the fan sensor first . Because it is this little part that switches the fan on ,and off . Not expensive to buy . Looking at the year of your car i would say is that all it needs is a reset . But as for how i am lost other members will help you asap .

 

[ashtonhill]

Ok thanks. Will look into it!

Tried to reset the ecu tonight by leaving battery disconnected for an hour or so but didnt cure it!

Sent from my SM-G950F using Tapatalk

 

[ashtonhill]

Can anyone help?

 

[paul73mt]

when you take your keys out how long have you waited whilst the fan still running as mine does it every so often (normally when finishing a regen )

 

[Merkaholic]

Paul73 has hit the nail on the head......assuming its a diesel. My CLS was doing the same thing. Got the dpf removed and then remapped. Since then its been fine.

Ps. Dont want to turn this thread on the legalitys of dpf removal. Its a personal decision.

 

[ashtonhill]

Thanks for the replies. Yep it is a diesel.

I'll admit to have waited for no more than a few minutes after the fan has come on however it turns on with the ignition immediately regardless of whether the engine has been on or not. Yesterday I hooked the battery back up after it sitting for 24 hours and immediately the fan came on! I think DPF is showing 50ish% full.

Yesterday I hooked up my Carsoft MB11 to it and had a look to see if i could find any issues again. All was well bar the Front SAM that was showing the day time running lights to have a short and not be working even though they were working fine! I couldn't find any oher useful information so disconnected the Carsoft and turned the ignition off and...........the fan didnt kick in!! 5 minutes passed and I thought great its fixed itself. To be sure, I turned the ignition on again and then off again and the bloody fan fired up 30 seconds later and continued to do so each time i tested it!! Must be an ECU or Sam issue I guess. All temperatures readings given by the ECU seem fine so cant see it being a sensor issue.

 

[Merkaholic]

Im prettt sure the regen mode is the cause of the fan coming on.

 

[ashtonhill]

Thanks, How can I check this?

 

[Merkaholic]

This is JUST from experience. I found that when the car was in regen mode the engine would be very hot. To the point some of the supposedly non conductive metal components were becoming very hot. Since i have had the dpf removed and reseted i have not had any issues.

Ps. My info does not constitute a mechanical diagnosis.........just merely a laymans observation.

 

[paul73mt]

Your DPF sometime will regen even when its not showing full as it some times does it on mileage also. They also do two types or regen i believe 'passive' and forced

 

[Joesoap17]

Perfectly normal for a car to cycle fan for a few minutes after shutdown to assist in heat soak.

 

[Uky]

One thing that can be good to know, even if this is not the cause here is that the Fan will automatically run at highest speed if the fan controller looses the CAN/LIN connection with the rest of the network. This to make sure that the engine should not be damaged. So if something like this starts to happen, a thorough check of all wiring and connections in the engine compartment should be done.

 

[p2djx]

This is VERY VERY interesting. Some of you may have seen my DPF related thread and numerous updates. I will update the original thread after posting this comment. However the long and short of it is that the car is currently in the 3rd garage for the 5th attempt and finding the cause of my DPF issues, Latest update is that they think the fan is faulty as the car has started, but never completed a regeneration for quite a few cycles. thought this strange but after reading this makes a bit more sense. Still waiting on word on if its been fixed and when I can expect my car back.

 

[ashtonhill]

No further with this at present. Fairly sure fan is not receiving signal from ECU. Need to investigate all fuses again, pre-fuse box and sam unit before considering ECU.

 

[ashtonhill]

Update: Had the car with a Merc Specialist with STAR and they cannot find anything pointing to why the fan is coming on when the ignition is switched off. They at present are recommending the replacement of the fan unit at considerable expense! Getting desperate to sort this now!

 

[pembssurf]

I very much doubt a new fan would fix the problem unless there was a very obvious short in the circuit.

 

[ashtonhill]

I agree but I have managed to source a used unit with motor and module for £75 so will give it a go and if no change then stick it on ebay. Still think something on the ECU is amiss. Anyone here had a used ecu reprogrammed?

 

[MancMike]

Your DPF sometime will regen even when its not showing full as it some times does it on mileage also. They also do two types or regen i believe 'passive' and forced

DPFs have an accumulation sensor that measures the percentage of soot accumulation.

Passive regeneration is just when your driving meets the requirements for regeneration, like a long steady 20 mile motorway blast holding onto a lower gear.

Active or forced regeneration normally has to be triggered manually if the car goes into limp mode because of soot accumulation because it wasn't able to clean it passively, It'll lift the revs to about 3.5k and hold them there, after a few seconds, you'll fill the street with black smoke and then it'll run clear, that's the DPF cleaned...

I had to force it on my mrs insignia via my diagnostic software, it was a pretty intense few minutes!

 

[easyonthegas]

As you do - I have a W204 radiator fan unit in my shed. Is 6 month old when removed by dealer (from C250 MY2010)

Contact me if anyone interested