Coolant symbol came on although everything seems fine

You could also check the fan operation by pressing BOTH AUTO buttons on the a/c control units simultaneously for 15 to 20 seconds. The fan should turn on at the highest speed.

The fan module on your E320 is mounted under the car at the left front frame rail.

If you had a MB scanner or equivalent, you could have exercised the fan unit at different speeds selectively.

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.

When you start the car with engine cool the fan should not turn at all (ECT < 70 degrees C and a/c off). As the engine starts warming up the fan gains speed up to the full speed. If you observe the variable fan speed behavior, the fan should be fine. As far as I can see there is nothing that monitors the speed of the fan for your car (2 wires from the controller to the fan). There are some fan versions that the fan rpm is monitored and and a fault is generated if the fan rpm doe not meet the spec., however, I do not think yours is one of them.

Have you checked the fault codes with a scanner ? There is a P0801 code regarding the suction fan controller, but I am not sure how the SAM unit detects the fan / fan controller issue, or whether it applies to our cars. Maybe when the fan is turned on to a full blast the SAM unit checks the PWM line voltage level which should be at ground level. Unfortunately I do not have access to the internal logic of the SAM.

You can try your scanner, or if you have an access to a scanner like MB Star, it would make the diagnosis much simpler, as you can read the internal codes from the SAM and the ECU, and also test the fan unit at various operational stages. My car has fans in the font of the radiator, so it is different from your car's single electrical fan. With my scanner, I could check the fan speed in percentage, and who requested the fan operation (engine coolant temp, or a/c). I can turn the fan on at different speeds so I can test the controller and the fan.

I tend to agree with you, based on what you are posting the wiring or the fan controller are the main suspects. To some degree there may be a problem with the SAM but it is difficult to diagnose this without the SDS or equivalent.

Do you observe the coolant temperature at the instrument panel or the a/c controller menu display ?

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.