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2003 E500 electric fan at 100% all the time

7K views 10 replies 7 participants last post by  Smartchoice 
#1 ·
Not my car, a buddy's.

He bought a clean 2003 E500. The electric radiator fan connection has previously been tampered with. The two smaller wires (control wires) have been cut and stacon-spade terminals been added by the PO.

The fan runs 100% all the time.
If one of the stacons is disconnected, the fan turns off.

He has checked continuity on the blu/blk wire to the ecu, and there is no continuity; it's open. Is there another device between the fan and the ECU?

What else should he be checking?

Are the two wires control wires? Is there a built-in really at the fan?
Can somebody describe the control operation of the cooling fan?

He did buy a new fan and it has the same issues, so it's not with the fan.
 
#8 · (Edited)
Hooked up my reader (Launch x431gds).

Fan is running 100% with key on.

Neither the engine nor the ac are calling for cooling; both are at 0%. The same screen shows fan at 0%.

I then went to check function and no matter if I add percentage to fan speed or reduce percentage, the fan remains at full speed.

So now I am thinking there must be a relay for the output of the computer, since the power wires are so large.

Alas, buddy does not have a fuse/relay chart in the driver's side fuse box. Go online, and it looks as if O is the relay, and located in the fusebox in the engine bay right in front of driver.

Is it O that controls the cooling fan?

I pulled that relay and the fan continues to run.

So I must be looking at the wrong relay.

Anybody know for sure which relay controls the cooling fan, and its location? I'd like to see if that relay has fused load side contacts.

EDIT - the only code relating to the fan is:
P2073-004 Electric suction fan for engine or air conditioning open circuit (P1999)
 
#9 ·
There is no fan relay on a W211 (that I know of). The mistake happens when people read the description of the relay they think is for the fan. That item is described as the "FANfare Horn" relay; what its for is obvious, but I think people see it and say, "There it is! Fan!" On YouTube, you will see a "mechanic" pull that relay out and declare it to be the radiator cooling fan relay.
 
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