Hi everyone,

I noticed my 2004 CLK 320's radiator fan ran on full blast (very loud) about 1second after I turned the key to position 2, and stayed on full blast when the car was running (no matter A/C on or off), and would only stop when I turn the key to OFF. All fuses are good and the coolant temp, no engine checks light or code, The only message is “Coolant / visit workshop”.

Can someone please confirm what could be wrong to cause the radiator fan to be on full blast?

Thank you in advance for any input or suggestion.

 

The coolant temperature sensor is probably shot! What does the temperature gauge on the instrument panel show?

 

As Anker mentioned, the temperature sensor is likely shot, may have a bad/corroded connection or could simply be disconnected.

According to AMG Engineers, it's important to maintain engine temperature as close to 180 degrees as possible.
http://www.autoblog.com/2012/12/12/a...sty-christmas/

 

normal temperature on the instrument panel, between 80 and 85 degree celsuis.

 

Does the fan come on when you first start the motor? Even after it's completely cooled down overnight?

 

the fan run on ignition 2 and when start the engine and even when engine is cold at the morning.

 

If it shows normal temperature on the gauge I suspect its the fan relay that is bad.

Another option, I hope not, is a short, but that is very unlikely.

 

I took a look at WIS and it appears that the fan control unit is built into the fan. If I am right you may have to replace the fan itself.

 

First scan for codes. The ECU controls the suction fan speed. It will run it on high if it cannot determine the engine temp, or if it thinks you need max AC cooling. If all of that is working properly, check the wiring to the fan to make sure it's not broken and is securely plugged in and not corroded. If all that is good, then it probably is a bad control module on the fan itself.

 

I would suggest as much as trouble shooting as you can before buying a new fan. I had a cooling issue on my old c55 and after swapping the thermostat I thought for sure it was the fan relay. As mentioned above, the relay is built into the fan so that set me back around $650 I believe. Installed it myself and still didn't work. Even dropped it with an Indy to see if it needed to be reprogrammed for any reason, still the same problem occurred. I regret not troubleshooting more on my end before dropping that cash.

 

thank you all,
and i would like to inform you that after a deep scan the problem was solved, it is a bad ECU and it was replaced.

 

Hello, am happy that you resolved the issue. I apologized, I want to jog your memory, were you experiencing a "no start" when the fan came on on key position #2? I am experiencing a no start and fan is running when key is n position #2. I am scared if it's the ECU. This symptom occur after washing the car, and I haven't started since (24)days. The new battery in now drained after 14dys. Any suggestions?

respectfully and valued
arjuan

 

Hi All, as this is a very old thread, I thought it might still be interesting because just had this issue.
With thanks to all who have replied to this before, Suspecting Temperature sensor and ECU goes way too far.
I had the exact same symptoms on my 2004 W209 with M112 (240) . All light come on when turning the key (except Water Temperature which remains 0 or blank) and few seconds later the Radiator Fan goes on full speed.
It turned out to be from the start enable relay (K40 ?). It is one of the black relays on the front SAM. Marked with Red Cross in my photo.
I opened the casing of the relay and pushed it by hand and Voila everything worked.
Just to make sure I swapped the two black relays and the symptoms changed. So, that was our bad guy.
Hope it helps.

 

.

 

Hi. Yes, same symptoms.
key on position 2. Nothing happened first. No starter. No error, then Radiator Fan started on high Rev. until I turn the key back. In that time the water temperature shows maximum. One i replaced the black relay everything was ok again. I don’t thhink your ECU would be faulty.
try this relay first.
regards
adrian

 

Thank you so much for replying rapidly, brother i am facing this same issue and i have swapped the old relays but haven’t found and improvement but as you suggested to buy a new relay and i got this issue of no crank and no start after a carwash from bottom with underbody panels removed after a oil cooler job and after 2 days the car stopped working and after drying up each and every coupler with blower and still car not started and then i opened front sam and i found bluegreen oxidization and i have cleaned it with petroleum and i i have cleaned a central gateway too i found some traces of oxidation there too and checked all fuses all are good but still no progress fan running as max at 3 position of key and i wasn’t able to connect with ecu but one day out of the blue the ecu communicated with obd and i got 6-7 code related to tcu and various other codes i have scanned my car with launch diagnostic tool

(Transmission Control Module
Abnormal®

C100 No CAN Message Was Received From Control Unit Engine Management

D10B No CAN Message Was Received From Control Unit Engine Management.
-
ESP - Electronic Stability Program
Abnormal

4840 Inspect Rpm Sensor.

SRS - Supplemental Inflatable Restraint System
Abnormal

The Resistance Value In The Ignition Circuit Containing Component R12/2(Front Passenger ETR Ignition Squib) Is Too

91A3 High. Note: On Vehicles With Special Equipment 'PRE-SAFE, Component R46/1 (Front Passenger Buckle ETR Squib) Is Installed Instead Of Componeht R12/2(Front Passenger ETR Ignition Squib).
RevER_LF_Left Front Reversible Emergency Tensioning Retractor
Abnormal

5024 Fault In CAN Communication With Control Unit ME Motor Electronics.

5025 Fault In CAN Communication With Control Unit ME Motor Electronics.

5026 Fault In CAN Communication With Control Unit ME Motor Electronics.

I will be very nice of you if you help me