edsaad

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.

Anker

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

Spectre-13

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/

edsaad

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

Spectre-13

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

edsaad

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

Anker

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.

Anker

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.

Rudeney

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.

JakeMS3

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.

edsaad

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.

jwb007

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