[gregNwt]

Hi All,
My W202 C200 (right hand drive) had the coolant level indicator light come on.
Testing the Coolant level sensor and Wiper level sensor shows they are not at fault (110ohm and 179 ohms), and bridging the contacts on their plugs (zero resistance) cause the Wiper level light to come on also. Running a magnet over the coolant sensor gives a low resistance (0-5 ohms).. If they are unplugged (very high resistance) the coolant level lamp stays on but not the wiper level light. So I am pretty sure the sensors are ok.

The owners manual indicates the engine fan (electric aux fan) not working can cause the light to come on.
The easy to find 40amp fuse to the aux fan is ok. (On right hand side engine bay)

I have seen reference to another pre-fuse on other models of merc with the Electric Suction type fan and hints where to find the pre-fuse blocks, but I can't find them on the W202 C200.

Can anyone tell me where I should look to find the pre-fuse for the electric suction type fan on the W202 C200 ??
Have looked in the relay compartment behind the fuse box mentioned above, near the 39 pin connector and relay box on left side of engine bay, and in the boot near the battery.

Also how can I force the electric fan to come on ? Maybe bridging the engine coolant temp sensor to see if the fan comes on if it thinks the engine is hot ? I had no luck with that but if the pre-fuse is blown that may be why ..

There seems to be a lot of coolant light on threads that say to replace the coolant level sensor and the wiper level sensor but few mention the fan also being responsible for that light to come on.

Any suggestions welcome.

 

[Patman1]

Well the two sensors are wired together. Short circuit = low wiper fluid, open circuit = low coolant, so by your analysis it looks like the sensors are working well. I never heard of the coolant light indicating a fan problem, but if the owner's manual says so, that's because it does! Bridging the contacts on the coolant temp sensor won't do you any god, you basically made the car think the coolant was cold! Simply unplugging the coolant temp sensor should make the fan turn on to full blast, as the ECM will assume a worst-case scenario and the coolant is overheating, so it will command the fan to go to full. I'm fairly sure the electric motor in the fan is an induction motor, so try reading the ohms across the fan plug, they should be really low, like 0.5 ohms type low. That can rule out a problem with the fan. Otherwise, you will have to start testing the logic chain and whatever components supply power to the fan.

 

[gregNwt]

Thanks Patman1, I had unplugged the temp sensor but the fan didn't come on. Will have to find the pre fuse part of the circuit and test the control module for the fan (N76) to drill down the parts involved ...

Have Attached the diagram of the Wiper/Coolant level circuits. That shows the fan motor M4/3 effecting the warning level lights...
In the owner manual where it expands on the instrument cluster lamps, there is this bit "C180, C200, C230 C230 Konpressor with air conditioning , if the coolant is at the correct level the radiator fan has failed"

There is possibly a pre-fuse block with a electric suction type fan 50amp fuse somewhere, and the N76 control module possibly hiding in the right side inner fender ...

WIll need to examine more.
Cheers
Greg

 

[gregNwt]

Update in case it is of any use :-

The level sensors seem to be good. But the electric (suction type ) radiator fan is problematic.

Turning on the A/C the fan will spin slowly, but only 50% of the time. That is sometimes it wont turn on at all. The speed is controlled by a pulse width modulation from the ECU to the control unit. (from either the A/C or temp circuits)

The engine coolant temp sensor is new and with in spec for resistance vs temp, but bridging it to make the ECU think the engine is hot wont cause the fan to spin as you may expect. (My diagnostic software indicated hot is lower ohms cool is more ie 30 degrees C around 1.4k )

Putting 12v on the fan directly makes the fan spin at full speed. So the fan motor is good...

While I have not seen the pulses to the fan control unit from the ECU I have bravely assumed they are getting there and it is the fan control unit (Part originally 0185459932 superseded by 0255453332) ... Now will need to see if a replacement will fix the coolant level light and it will go out...

Wish me luck.

...

 

[paul1123]

Update in case it is of any use :-

The level sensors seem to be good. But the electric (suction type ) radiator fan is problematic.

Turning on the A/C the fan will spin slowly, but only 50% of the time. That is sometimes it wont turn on at all. The speed is controlled by a pulse width modulation from the ECU to the control unit. (from either the A/C or temp circuits)

The engine coolant temp sensor is new and with in spec for resistance vs temp, but bridging it to make the ECU think the engine is hot wont cause the fan to spin as you may expect. (My diagnostic software indicated hot is lower ohms cool is more ie 30 degrees C around 1.4k )

Putting 12v on the fan directly makes the fan spin at full speed. So the fan motor is good...

While I have not seen the pulses to the fan control unit from the ECU I have bravely assumed they are getting there and it is the fan control unit (Part originally 0185459932 superseded by 0255453332) ... Now will need to see if a replacement will fix the coolant level light and it will go out...

Wish me luck.

...

Hello,
I would like to refresh this topic.
I have problem with my M4/3 Electric suction fan engine/ A/C. Last time I washed my engine and after this occurs an error: the coolant level indicator light come on. I put new B11/4 Coolant temperature sensor and N76 Engine/AC electric suction fan (check coolant and windshield washer fluid sensor - ok) but it doesn't help. My fan runs ok for a few minutes, then coolant level indicator will on and suction fan is working like: 4 seconds on and 2 seconds off, it causes that temperature is rising up.
I check attachments and wonder what task it performs L5 Crankshaft position sensor ?

What else is related to fan operation ?

Thanks !

 

[C class zed]

Update in case it is of any use :-

The level sensors seem to be good. But the electric (suction type ) radiator fan is problematic.

Turning on the A/C the fan will spin slowly, but only 50% of the time. That is sometimes it wont turn on at all. The speed is controlled by a pulse width modulation from the ECU to the control unit. (from either the A/C or temp circuits)

The engine coolant temp sensor is new and with in spec for resistance vs temp, but bridging it to make the ECU think the engine is hot wont cause the fan to spin as you may expect. (My diagnostic software indicated hot is lower ohms cool is more ie 30 degrees C around 1.4k )

Putting 12v on the fan directly makes the fan spin at full speed. So the fan motor is good...

While I have not seen the pulses to the fan control unit from the ECU I have bravely assumed they are getting there and it is the fan control unit (Part originally 0185459932 superseded by 0255453332) ... Now will need to see if a replacement will fix the coolant level light and it will go out...

Wish me luck.

...

Sorry its 5 years too late. Im curious to your conclusion if you remember! Im having a problem where my coolant light is on and my fan is staying on. Did you fix it with a new fan control unit? Thanks