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Coolant symbol came on although everything seems fine

4072 Views 22 Replies 4 Participants Last post by  alpac
Hi Folks,
Today was a pretty hot day over here, 94 degree. My wife took the 1999 E320 to go downtown. After about 25mns of driving in stop and go traffic the engine coolant symbol came on. She said the car never overheated, the temperature gauge went close to 90 but not more. The engine coolant symbol stayed on until she came back home. As soon as she was home I checked the car and could see that indeed the coolant symbol was on but no engine light. I stoped the car, checked if there was any error code in memory with my OBD2 reader but there was nothing. When I started the car again after only a couple of minutes not running the coolant symbol was gone and never came back even after letting the car iddle for 15mns in hot weather. There is plenty of coolant in the reservoir so it is not a low coolant problem. The fan seems to run fine so I am wondering if there is a sensor somewhere that is sending a wrong message. Any idea?
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Thanks. Last fall I replaced the Coolant Temperature Sensor that is right under the air pump because the previous one was sending an erratic message to the ECM which created a lot of engine hesitation. I did not know there was another coolant sensor under the expension tank. I just came back driving the car and the message came out again very briefly and it actually displays the words "Engine" and "Fan" and the radiator symbol in between the 2 words.
Ok so i need to replace the fan controler. Where is it located?
check the link out. it is figure 6. The item is N76.

STAR TekInfo

The pricing (remove the part and make sure you have the right part number that matches in the following link)

Mercedes A 0255453332 Radiator Fan Controller/Resistor

It could be a loose electrical connection too. Make sure the connector is tight and clean the contacts with electrical connector cleaner, or MAF cleaner.
Excellent. I wil start with checking the connections. THANKS
The diagram is pretty difficult to read even when magnified. Also I looked at the photo of the part on amazon and tried to find the same part in my car around the fan but could not. Is the Auxiliary Fan Control Unit located inside that black cover at the center of the fan like the diagram seems to indicate?
And the tip for getting a better picture is to click on the "printable version" button at the right top of the diagrams. You will have the PDF version which is clearer.
Ah! ok. Mrboca you rock. Big thanks again for your help.
Thanks again folks. I will look at this sometime this week after work an will report back. I am booked all day tomorrow for the baby shower of my first grand child. Jeez!! I feel too young to be a grand dad :)
Today I unplugged the fan controler unit that is under the driver side headlight and sprayed contact cleaner. I also checked the wiring and it does not look damaged although it is wrapped under a plastic cover so if the wire was bad underneath I would not see. Anyway I plugged everything back and went for a 30mn ride in hot weather and I did not get the error message. Since the message appreared randomely before I will have to drive the car for for sometime with no message to claim victory. From what I could see of the fan control unit from underneath the car replacing it will need to remove the front bumper so as to reach the screws that hold it.
Thanks again for your help in locating this module.
Today after 25mns of driving and a 5mns stop at a shop the message came back within 2mns after I took the car back. Back at home I checked the radiator fan operation by pressing both "auto" buttons on the a/c for about 15sec and indeed the radiator fan speed increased quite a bit but that also triggered the message to be displayed. I turned off the engine then started it back and the message was gone but when I pressed the 'auto' buttons for 15sec that again triggered the message to be displayed as well as the fan speed to increase. So what seems to happen is that everytime the fan is instructed by the controler to go full speed it also triggers the message. Do you still think this is a controler issue or a fan issue? I am thinking that the fan either works or does not and it does work in my case. So that leaves the fan controler to be faulty or a bad wiring, right?
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mrboca, thanks again for your usual very detailed answers. There is no code rendered that I can read with my generic scanner. Unfortunatly I dont ahve the MB Star scanner but I may need to invest on one now that I have 4 different Benz's. The fan indeed does not turn when the car is cold and starts turning after the car gets warmer and I dont get this message right away. As I said in my previous post it looks like I get the message only when the fan is supposed to go full speed. I will start by better inspecting the wiring and then if nothing found I will replace the controler.
I am reviving this thread that I started several months ago. I never took the time to replace the fan controler that was possibly the cause of my Engine fan message displayed on the dash and whihc made me start this thread. Beside displaying the message when the car was hot and when the radiator fan was running at max the car never overheated and ran fine until now. Since yesterday though additional symptoms have appeared which I am wondering if they could be linked to the same cause that is to say a failing fan controler. For a couple days now the Engine fan message appears everytime the AC starts. As before the car never overheat and tmep stays always in between the 80 and 90 marks when hot. Today my step daughter was driving the car and she said she turned the AC on which triggered the Engine fan message on the dash and then the car stalled. She tried to start the car again the car would crank but would not start. She tried to start the car 10mns later and the car started and she was able to come back home. There is no error code in memory that my standard OBD2 reader can find. Beside the engine fan message coming on and the AC not blowing cold the car runs fine for now. One of my next move is going to be to replace the fan controler. I am not sure if the engine fan message issue and the car stalling today are related to the same fan controler problem or if they are 2 different issues. Of course the problem with the engine stopping when hot and not starting again after 10 mns make me think of the infamous cranshaft position sensor issue although it had already been replaced back 50kmiles and 5 years ago. I would think that a CPS issue would render an error code would it not? I appreciate idea or any though you folks may have about this.
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Here is an update. after my last post I checked the pressure of the AC and I was expecting it to be low since it only blew hot air. To my surprise the pressure was very high, close to 200psi! when the normal should be between 30 and 45psi. I have no idea how it got to that level. Anyway, I pushed on the AC valve to release the pressure until I got to the normal range. I then took the car which was already warm for a 20mns test drive. The AC worked wonderfully, it blew nice cold air and today the outside temp over here in Raleigh is close to 90F. The engine temp remained in between the 80 and 90 mark. The engine fan message never showed during my test drive while as I explained before it would show everytime the AC was turned on. So it looks like there is some kind of correlation between the engine fan message and the AC pressure. I checked the AC pressure after my test drive and it was OK.
The engine did not stall on me during the test drive although I turned it off and on several times, one time after 5mns waiting. Should the CPS not trigger and error code? Anyway I will drive the car all the week-end and see if the problems reoccur.
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200 psi is a lot for the low side. works out almost 14 bars which is typically what you see at the HIGH side. That is what happens when the compressor is turned off due to overfilling and when the expansion valve is fully open.

Check your sensor values through the hidden menu on the a/c controller. especially for the refrigerant pressure when the a/c is running (#7). How to do it should be in the stickies (press and hold REST button).

When the high side is so high due to overfilling, the a/c controller asks for maximum cooling to remove heat from the condenser, and to reduce the high side pressure. That is why when you turn on the a/c, you get the maximum airflow demand, which generated the fan fault. When you reduced the pressure, the airflow demand wendt lower, so the fan message did not show up. I guess you can still get the fan message by pressing the AUTO buttons simultaneously to demand highest fan speed, for testing and confirmation.

So, the demand from the refr. overfill is more likely the symptom, rather than the cause, if the fan test action confirms it.
Thanks again mrboca for your always detailled responses and logical explanation
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