Hi all,

I have an 04 S500 with an engine fan issue. I've checked fuses and replaced the motor/controller. Am I missing something?

 

Sorry it's not coming on

 

Is the commanded fan value going up and the fan doesn't move?

Are you sure good power is getting to the controller?

 

WDBNG84J34A423365

 

I don't know... I'm going to pick up a volt meter tomorrow when I get off work.

 

You need a scanner that can see the desired fan percentage, like Star or similar. If you see the fan desired % go up and the fan doesn't move, the issue is in the fan itself. If it isn't, check the temp sensor and the a/c pressure sensor, although if they were out you'd have other problems.

If the fan isn't coming on when the M/E asks it to, either there's no power on the large wires coming in, or the small data wires coming in aren't sending signals to the controller. Or the controller is bad, or the motor is bad, but you said you replaced those.

 

FWIW I had fan issues on my first CL and it was cheaper to replace the entire fan assembly than to mess around with just a controller or motor, the replacement procedure is a bit of a PITA on the 600 cars though.

 

yes I did replace the controller... What's the M/E?

 

M/E is Motor Electronics, what MB calls the engine computer. I'd have to look at the specific diagram for your car but most of the fan systems have the desired fan signal sent from the engine computer to the fan controller, then the controller sends the voltage to the fan to get the desired speed.

 

so there is a possibility of a bad ecm?

 

Always a possibility, but you must diagnose it properly to find out. No reason to guess when you can have it checked and tested.

 

I noticed that the compressor wasn't coming on, so I checked the refrigerant and low and behold it was low. I then added 24oz and the compressor switched on as well as the fan...

I will keep you guys posted!!!

 

So just having low AC refrigerant can screw up the fan on these cars !

 

Apparently so... Even though the fan is spinning it's doing so at a low speed.

 

The AC is one of the factors that control fan operation. Whether the AC is on or off, or even works, should not affect how the engine temperature controls fan operation.

 

I have a 2004 S320 cdi that fan comes on when ignition is switched on and blows like 747 on take off.It switches off when ignition is off.Does the fan get controlled by a SAM or ecm
the diagnostic on engine shows no fault codes but shows fan is on 90% operation. it has a 648.960 motor

 

I had a fan problem on a 928..didn't even know it till I got stuck in a traffic jam. They were seized up...one barely turned...the other not at all. Have you tried seeing if they spin freely by hand? I found used ones from a California junk yard for $350 for both...the dealer wanted $750 a piece.