C63 AMG (W204) 2008 - 2015
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Engine fan ON at all time.

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Old Jan 15, 2019 | 10:20 PM
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Viper 1994, ZR-1 1991 and RX-7 1993
Engine fan ON at all time.

Hello,

Cold weather here, northern Quebec. Average -12°C (10°F).

Engine fan turns on (and stays on). Coolant temperature shows a steady 91°C (196°F).

Heater blows not so warm air.

No CEL, however when I read the codes there is something (sorry didn't note which code it is). When I erase the code, fan turns off instantly, and sometimes the problem is solved for the rest of the day. Next morning, fan is still off until engine reaches some temperature. Have to erase the code again...

I don't even think I need that fan right now to be honest. I tried to pull fuse #22, without success. Is there a way I can temporarily disable the fan until I figure out what's the issue?

Thanks!
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Old Jan 15, 2019 | 10:31 PM
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So you have a code and fan is not working right, you clear code and fan works right.

So guessing code will tell you what is wrong, maybe make note of it and don’t clear it.

car can still overheat if idling at any temp so would not recommend disabling fan, but easy way is unplug fan harness at the fan.
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Old Jan 15, 2019 | 10:40 PM
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Viper 1994, ZR-1 1991 and RX-7 1993
Originally Posted by roadkillrob
So you have a code and fan is not working right, you clear code and fan works right.

So guessing code will tell you what is wrong, maybe make note of it and don’t clear it.

car can still overheat if idling at any temp so would not recommend disabling fan, but easy way is unplug fan harness at the fan.
Well exactly. When I got the code, fan is ON at all time, until I erase it.

Before I had that problem, I never heard that fan running (I only drive the car in winter time). It is very cold and windy here. I'm sad to read that the car could still overheat.
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Old Jan 16, 2019 | 08:57 AM
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Thermostat.
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Old Jan 16, 2019 | 10:04 AM
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Viper 1994, ZR-1 1991 and RX-7 1993
Originally Posted by Jasonoff
Thermostat.
Well that's what I thought too, but why everything is OK when I erase the code?
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Old Jan 16, 2019 | 10:13 AM
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Originally Posted by MangeDlaMarde
Well that's what I thought too, but why everything is OK when I erase the code?
Intermittent failure maybe. Check the connector.
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Old Jan 16, 2019 | 11:16 AM
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Originally Posted by Jasonoff
Intermittent failure maybe. Check the connector.
All connectors tight. It is not intermittent, every morning first time it gets hot fan gets on and stays on until I erase the code.
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Old Jan 16, 2019 | 11:29 AM
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Sounds like the thermostat has failed (stuck open). It throws a code when you first start the car which turns the fan on high. Clearing the code returns the fan to normal operation.
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Old Jan 16, 2019 | 11:41 AM
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It's the thermostat. Mine did that too but I had a code for it. Stopped doing it once I replaced it
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Old Jan 16, 2019 | 11:46 AM
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Sad! I just ordered the 26$ coolant temperature sensor from the dealer, I was hoping it would be enough...
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Old Jan 16, 2019 | 01:17 PM
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Again this morning: OBD2 scanner shows 0 code, however when I erase everything the fan stopped. Been running for 60 kms afterwards, everything runs as it should.

Before I erased the code, temperature was at a (solid) 91°C. As soon as I erased it (5 seconds later), it dropped to 70°C...

Thanks for your help guys.
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Old Jan 16, 2019 | 01:38 PM
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It's a Thermostat, is given your ECU conflicting signals. I had the same type of issue but with my Oil Temperature Sensor, thereby causing my oil cooler fan to run.
We replaced the sensor, reset to parameters in the ECU using Star Diagnostics, and problem solved.
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Old Jan 16, 2019 | 01:51 PM
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Originally Posted by Yuille36
It's a Thermostat, is given your ECU conflicting signals. I had the same type of issue but with my Oil Temperature Sensor, thereby causing my oil cooler fan to run.
We replaced the sensor, reset to parameters in the ECU using Star Diagnostics, and problem solved.
So are you suggesting that it could be the coolant temperature sensor?
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Old Jan 16, 2019 | 02:06 PM
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Yes, but the only true way to know what it might be, is to have diagnosed.
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Old Jan 17, 2019 | 11:30 PM
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Well I'm trying to figure out WHERE IS that coolant temperature sensor... I can't find it! Searched everywhere!
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Old Jan 18, 2019 | 09:57 AM
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It may not be the thermostat.
Get a Xentry scan of the car.
I like to mess around in Xentry and try all the tests and things.
I tried a reset once and it turned the fan on permanently. It may have been the inidovual test /reset for the cam adjusters, not the teach in process.
Then I did a general reset and this was solved.
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Old Jan 18, 2019 | 10:02 AM
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Originally Posted by Vladds
It may not be the thermostat.
Get a Xentry scan of the car.
I like to mess around in Xentry and try all the tests and things.
I tried a reset once and it turned the fan on permanently. It may have been the inidovual test /reset for the cam adjusters, not the teach in process.
Then I did a general reset and this was solved.
It seems like the problem happens more and more often when it is very cold outside.

I broke a nipple on the thermostat so I've got to order a new one anyway.

But I still couldn't figure where that coolant temperature sensor is.

Very limited information about these cars here. Maybe I should post a DIY.
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Old Jan 18, 2019 | 01:00 PM
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Here you go. From ALLDATAdiy



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Old Jan 18, 2019 | 01:25 PM
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Originally Posted by Mort
Here you go. From ALLDATAdiy


Wow thanks a lot sir!

However it seems to be pointing to the passenger side of the engine, at the front. So I thought the sensor pointed out was the OIL temperature sensor?
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Old Jan 18, 2019 | 01:54 PM
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The oil temperature sensor is on the left side of the engine behind the AC compressor.
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Old Jan 18, 2019 | 08:34 PM
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Originally Posted by Mort
The oil temperature sensor is on the left side of the engine behind the AC compressor.
Very strange. Dealership gave me a diagram and right (passenger in North America) side was pointing to Oil Temperature Sensor, and almost dead center, and lower, was pointing to the Coolant Temperature Sensor.

I am confused now.
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Old Jan 19, 2019 | 12:57 PM
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Here is a picture from AllDatadiy. See the arrow in the middle of the steering linkage boot pointing to the location.


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Old Feb 5, 2019 | 06:15 PM
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Thanks a lot for your pictures Mort, maybe the dealership reversed both sensors...

Anyway, I did not change the sensor, but I changed the thermostat this afternoon. So far so good... I will post if the problem comes back!

Thanks everyone!
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Old Oct 29, 2025 | 05:38 AM
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Originally Posted by MangeDlaMarde
Thanks a lot for your pictures Mort, maybe the dealership reversed both sensors...

Anyway, I did not change the sensor, but I changed the thermostat this afternoon. So far so good... I will post if the problem comes back!

Thanks everyone!
Since you changed the thermostat, has the problem occurred again? My car has the same issue now.
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Old Oct 29, 2025 | 08:50 AM
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Originally Posted by EmmanuelScott
Since you changed the thermostat, has the problem occurred again? My car has the same issue now.
Hello,

Problem never came back!
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