Mercedes-Benz Forum banner

2008 ML350 Cooling Fan Intermittent

5K views 6 replies 4 participants last post by  Agentsnake 
#1 ·
Hello

first of all thank you in advance for all your replies :)

Well yesterday my wife noticed the coolant temp indicator came on so this morning I did start up the Benz and let it idle for some time and everything did appear to be ok.
After 10 min fan did kick in and I was a happy man walk away and call it a day.

Well after she did go on to a longer ride same problem she send me a pic from indicator in dash and after she came back sure enough at 230F coolant temp the fan was of and ac hot.

Anybody know what this could be or where to start. I did read people did replace cooling fans and had still same problems try to avoid to just buy parts for no reason.
Thanks in advance I will check tomorrow again if the fan still works when engine is getting warmed up and also if I turn AC on cold.

Thanks
 
#2 ·
A/C will be shut down when there is a cooling problem. Are you low on coolant when the eng. is cold?

You have to test the system at idle. Hood open, start cold eng. and turn on A/C. While eng. is warming up monitor the coolant reservoir looking for bubbles and the raising of the coolant level. Doing this process have wife checking for temp degree at the cluster.

Fan should kick on after specified time. Does the fan run at high speed for 20 secs. or so and then shut off? Then the fan should kick on again, and so on. Does it?

Your problem could be a closed thermostat or a faulty fan.
 
#3 ·
Ok thank you for your reply here some extra info I should have mention .... Water pump I did replace one year ago wife does not drive much so less than 7K miles on this. Also this year in Feb I did replace the thermostat because there was a code for it and after replacing code did not come back. Coolant is fine and I have programmer with long cord can watch coolant level and monitor temp on screen.
Also please keep in mind when the warm up process takes place and I turn the AC on the fan kicks on just like it should. The problem seem to occur only when engine has reached full working temp. this is what I will double check today.

So if the fan it self is working fine at warm up and when cold what could than be the issue with fan is there a fan module to switch out or only full assembly?

Thanks again
 
#5 ·
Yeah you are right I believe something is going on with the circuit board inside the fan because the control module is inside the fan as far I know.
I also know that MB did enclose this in a way so you not able to open it but I will open it and I think I already know what is going on I might do this next weekend but will come back and update with pics I hope I can fix this issue for super little money or even for free.

Thanks again and yall have a great Sunday
 
#6 ·
Fan speed is controlled by the ECU. The circuitry inside the fan controller is just enough to read signaling from the ECU and respond. It does have a fail-safe mode so that if it does not get a valid signal from the EC, it kicks into high-speed mode.

I do not know if your Autel unit can do this, but with SDS, you can test the fan controller by sending it signals to actuate it in 10% increments. Looking at all the possible causes of this fault as listed in SDS, the most likely culprit is a bad fan controller.
 
#7 ·
I did decide yesterday to take the fan assembly out real quick because this only takes 10 min anyway ....

Here are the pictures I did find a bad solder spot or lets say it appears bad to me on the circuit board you will find several bigger solder spots on the corners where 2 or even 3 pins are connected.

I did re solder all the major connections and used high temp heat gasket maker to but it back together so no moisture will get inside. Today my wife took the car to a longer ride where the problem in the past would occur and what can I say so far the light did stay of and fan works fine.

I will report back after 1-2 weeks and let you guys know if this was the final fix or not because this can save some people a lot of money the only difficult part is to get the back cover from the fan of I did use a little exacto knife to pre cut the sealant they used to clue to cover into place.
 

Attachments

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top