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#4758551 - 05/16/18 08:54 AM 1999 e320 aux fan wont stop running, BENZ pro
2008wrx Offline

Registered: 03/12/09
Posts: 189
Loc: CA
i am helping a friend of mine to solve the "AUX FAN WON'T STOP" running after we shut off the engine. This unit only has 1 electrical fan set up behind the radiator.
There are 2 unique scenarios, i tried them both when engine is cold and hot.
1: After we shut off the car, fan will keep spinning till the battery die. When engine is hot like 100 degree coolant temp; it will run till the battery die.
2: When engine is cold, you manually use your hand to spin the fan, it will kick star the fan, but it will only turn at very very slow speed.
Things have been done to solve this issue: New Aux fan, new climate control panel, new coolant temp sensor, new ac pressure switch, new thermostat, new fan control module.
Please help, thanks a lot.....

#4758620 - 05/16/18 10:03 AM Re: 1999 e320 aux fan wont stop running, BENZ pro [Re: 2008wrx]
SHOZ Offline

Registered: 06/28/03
Posts: 5807
Loc: Illinois
If the fan control module is the solid state electronic relay for the fan I would suspect it. When solid state devices fail it is usually in the on position. But it would be on as soon as you turn on the key I would think.
2008 Hyundai Accent 1.6L 5 sp manual hatchback
2010 Hyundai Genesis Coupe Track 2L Turbo 6sp manual

#4763289 - 05/20/18 06:34 PM Re: 1999 e320 aux fan wont stop running, BENZ pro [Re: 2008wrx]
VeryNoisyPoet Offline

Registered: 12/16/17
Posts: 318
Loc: Massachusetts
Sounds like some sort of short circuit in the wiring that is letting power bypass the fan controller and spin the fan, or trick the fan controller into keeping the fan on when the car is shut off.

Measure the voltage at the connector to the fan motor when the fan is stopped, and then use your hand to kick start the fan to see if anything changes.

Measure the voltage at the input signal to the fan controller to see what is happening there when fan is stopped, when fan is running normally, and when the fan turns slow after being started by hand.
1998 V70 GLT / 187k miles

"Use yah blinkah!"

"Be nice. The alternative involves an air horn and 7000 lumens of high beam."

#4763742 - 05/21/18 09:37 AM Re: 1999 e320 aux fan wont stop running, BENZ pro [Re: 2008wrx]
bmwpowere36m3 Offline

Registered: 04/29/07
Posts: 684
Loc: Connecticut, USA
Do you have a wiring diagram? You threw the parts book at it...

Without a system or wiring diagram its hard to say. Does the ECU communicate with the fan module? I'd be looking at wiring personally.