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For the past year I get engine fault code P0115 "Engine Coolant Temperature Circuit Malfunction" when I head into the mountains to go skiing. The check engine light appears as the temperature drops and stays on until I clear the code when I get home. Then I don't get the error message again until I head into the mountains again. Any ideas? And where is the Engine Coolant Termperature Sensor in a W210 4Matic Wagon?
 

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E320/E250 Bluetec Ford F350 6.7l
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Well , ain't our cars sensitive? I had similar situation with fuel temperature sensor on my diesel 3 years ago and with 2 plug cleaning jobs I still drive with it and CEL is not coming back.
So start with cleaning the plug and checking the wires for any damage.
Than go to Russian site if you want to check the sensor placement.
 

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Dallas, Texas
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For the past year I get engine fault code P0115 "Engine Coolant Temperature Circuit Malfunction" when I head into the mountains to go skiing. The check engine light appears as the temperature drops and stays on until I clear the code when I get home. Then I don't get the error message again until I head into the mountains again. Any ideas? And where is the Engine Coolant Termperature Sensor in a W210 4Matic Wagon?
You are driving around with partially stuck open thermostat.

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1999 E300 TD
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I would be curious to learn if there was a noticeable reduction in AC blower temperature??

I would also like to learn what the dash engine coolant temp indicator was reporting when the check engine light came on??
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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Replace the thermostat.
 

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1999 E55, 2001 E320, 1990 560 SEC, 2004 ML350, 2001 ML55, 1995 S500, 1998 SL500, 2010 E550 Sport zoo
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Also check and/or replace your coolant, if you are not the roginal owner then previous owner may have used wrong coolant and/or hose water (not distilled water) and bad coolant mix could have lead to the t-stat problem due to corrosion.

Good call WTK !
 

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2001 W210 E320
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mrboca I am having this issue, my suction fan occasionally stays on hi speed at the turn of the ignition to position 2. even before starting the car. And at other times behaves normally. However I have noticed that my radiator expansion tank never gets hot.... is this normal? With my other cars after a 50km drive... you dare not open the filler cap, but with my w210 e320 I can confidently open it and will dip my finger inside a lukewarm coolant.... what is missing? Thank you all
 

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1998 E320 base sedan @ 160kmiles
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You need to explain the problem a bit more clearly.

With the engine cold, you turn the key to position 2 and the fan starts at high speed. Is that it ?

What does the engine coolant temp sensor say at the instrument panel at that point ? what about the reading in the climate control system menu of the same ?

Typically if you have an electrical issue with the sensor wiring / sensor / connector, and the ECU cannot make anything out of it, it will turn the cooling fan on. Also an implausible signal for the refrigerant pressure can cause that, or a problem with the ECU.

Regarding the expansion tank, if the coolant warms up within 5-10 minutes of driving and keep the coolant temp within 80-90, I say don't worry about it. The coolant from the radiator expands and , a bit of it overflows into the expansion tank mixing with the much cooler coolant.
 

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2001 W210 E320
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You need to explain the problem a bit more clearly.

With the engine cold, you turn the key to position 2 and the fan starts at high speed. Is that it ?

What does the engine coolant temp sensor say at the instrument panel at that point ? what about the reading in the climate control system menu of the same ?

Typically if you have an electrical issue with the sensor wiring / sensor / connector, and the ECU cannot make anything out of it, it will turn the cooling fan on. Also an implausible signal for the refrigerant pressure can cause that, or a problem with the ECU.

Regarding the expansion tank, if the coolant warms up within 5-10 minutes of driving and keep the coolant temp within 80-90, I say don't worry about it. The coolant from the radiator expands and , a bit of it overflows into the expansion tank mixing with the much cooler coolant.
a. from cold start my suction fan starts after like 20 minutes of driving and stays on the high.
b. then afterwards it starts with the ignition in position 2.
c. I have a freon leak and my ac refrigerant needs a complete refill.
d. my instrument panel stays between 80-87 Celsius steady withing 8-9 minutes from cold start.
e. my ac controls is in safe mode...that is the ECON mode.
 

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1998 E320 base sedan @ 160kmiles
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You need to connect a scanner that can read the suction fan status (speed selected) and how much of the fan is due to a/c, and how much of it due to the engine coolant temp. Sometimes bad a/c controller cause this problem.

It should be in the ECU live data.
 
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