W202 C200 radiator fan failure

[gb metallic]

I have a W202 1998 C200 auto with AC.

Problem is last year after a dodgy steering lock that got replaced, after starting the car again, the dashboard coolant yellow light was on and every time you turned the ignition on, the fan would come up on at high speed. I ended up changing so many parts and still the fan would be constantly roaring at high speed only at times it may slow down and stop after driving for a while, only to come back on at high speed again.
Parts I replaced was the thermostat, low coolant fluid level sensor, temperature gauge/fan switch (screwed into the thermostat body), fan relay control unit, that is mounted on the inner nearside wheelarch, electric radiator fan. None of these solved the problem.
Eventuallly few months ago now the AC wasnt working, which was a dead AC compressor clutch failure. So got another one used and fitted it and AC was working again.
Now recently this week fan does not even come on at all and the engine shot up to near 120 deg C and I realised it was overheating and had to shut it off. I then realised the AC is barely working or it probably isnt. This is so annoying, it seems overcomplecated, even BMW does seem so confusing to fix a dadgy fan system, lol.

I have been trawling through the net for solutions. I have seen that someone said they replaced their dashboard intrument clocks unit to stop the fault of the yelllow low coolant light and fan problem; but I really dont know if that would solve it, seems a very strange one.
I have seen though that one person on here said the wiring from the fan relay in the wheelarch to the fusebox is bad. http://www.mbclub.co.uk/forums/engine/26076-w202-overheating-2.html

Does anyone know what wire in the fusebox itself does it lead to as I can not find any wiring diagrams etc on it and the Haynes appears to be very limited about the W202 compared to other cars. Is it the normal fusebox on the drivers side (o/s) windscreen. And what connector it is?

TIA

 

[BlackC55]

Stop throwing parts at it.

It needs proper diagnosis with a Star. The reason the fan is going all the time is because the car is in an emergency mode. There is a component that is faulty or incorrectly coded such as the ignition switch so the fan runs at 100% yeild to protect the engine.

I expect the fan has worn out due to it running all the time flat out but I am only guessing.

Get it on a Star.

 

[gb metallic]

The ignition switch is coded correctly as it was done by Mercedes themself.

I now have the fan running I had tested it with a separate voltage source by disconnecting it and connecting 12 v.
I then decided to trace all the wiring back from the fan control unit and realised a connector was loose underneath the fusebox, put it back in and the fan comes on again as back to square 1 when the ignition is switched on.

When I turn the ignition on, the cooling fan runs at full speed. If I turn the interior fan switch on, the engine cooling fan slows down in speed and if it is on full blast (the interior fan) on speed 6, the engine cooling fan would stop. You would hear the AC receiver/dryer making that click noise, but it does not seem to be running and you cannot see any movement of fluid in the siteglass. The air from the interior vents is warm even if the AC is switched to cold position. If I turn the interior fan switch off, the engine cooling fan would gradually come back on. The yellow coolant light remains on.
I have taken pics of parts and diagrams.

 

[gb metallic]

Diagram of the circuit posted. Does anyone know if there is any problem with the loom from the fan module unit A 202 540 935?

Both fuses for the fan being 38 and 41 are perfect. The connectors to the fusebox go at the bottom. There does not seem to be any relay on the fusebox for the fan.
Is there any components with the fan system missing.

 

[andy27168]

Hi,
I have a fan problem with my C43 "EXCEPT" my fans won,t run at all.
On my car these fans are their primarily for the A/C, as I have an engine driven fan on a viscous coupling for engine cooling, Though I believe they will cut in at a set temp on engine temp. if the the engine fan cannot cope.
The fans in my case are turned on and off by refrigerant pressure.
Yours I believe should be the same, the signal for the fans to operate comes from the heater control unit, this unit I believe also recieves an engine temp. signal as well, so it is triggers this under certain conditions.
The coolant level light is wired together with the washer fluid level switch, either of these two switches going faulty could put your coolant level light on.
But to be honest i think you,ll need to get it onto STAR and see what fault codes are present regarding your fan issue, though mine is not throwing up codes for them not to be running, it shows that there are no issues with the A/C, so mine I believe is the fan control module under the inner wing.

 

[gb metallic]

I would have to invest in a Star tester; any recommendations, ebay etc.

I got the air con running again. It was the Green/Blue wire that goes into the compressor on the engine. It had fray in it revealing the wire. So repaired it and now the A/C is blasting out cold again. Although the problem with the fan coming on and yellow dash light remains.

 

[garethmb]

Engine cooling fan on all the time

I had a new ignition switch fitted a week or so ago. This was done at a merc specialist not mb. When I went to collect the car, as soon as the ignition started, so did the fan. This never happened before. The garage say that they will look at it (of course for a fee). But why should i pay if the fault was not there before?! The garage say that its not there fault! I also have the engine light on on the dash. This extremely annoying!!!!!

After reading some of the posts in this thread, my thoughts may have been confirmed.

Question for blackc55.......If I have had a new ignition switch fitted could the incorrect programming have caused this?

I haven't yet started to throw parts at it, as what I have read at various places across the net it could be a number of things.

Cheers in advance.

 

[cmacleod540]

air mass it fixed mine

 

[NW_Merc]

If you take it along to your local independent MB specialist, he (or she dont want to sound sexist) will diagnose it as they will have a STAR diagnosis system. This will pinpoint the problem rather than you changing parts ad hoc. You could buy one of these systems but brand new they cost around 2.5k which isnt really pocket change. Used they will be around 800 pound (a member was selling one on here for £750). Bearing in mind that getting it onto star may cost you £65 for a session, buying the machine and then leaving it redundant for most of the year is a false economy in my opinion.

 

[geoffreyw]

Please let me know where the coolant temperature control sensor is on a CLK 200k 2000cc. year 2000.
Where is the best place to buy a replacement. Thanks, Geoff

 

[megabyting]

Diagram of the circuit posted. Does anyone know if there is any problem with the loom from the fan module unit A 202 540 935?

Both fuses for the fan being 38 and 41 are perfect. The connectors to the fusebox go at the bottom. There does not seem to be any relay on the fusebox for the fan.
Is there any components with the fan system missing.

Thanks for your diagram. Logically, Red/White and Blue/Green are the logic signal for the PWM (Pulse width Modulation for fan speed control), the brown cable (31) is 0V, Red/Yellow (30) is 12V supply. M- and M+ are the power output to the DC motors.

I experienced the fan ran at highest speed because the insulators of the cables of the coolant temperature sensor disintegrated due to aging and caused a short circuit. The controller sensed the water temperature was very high, and turned on once the key was turned to the on position. The solution was to replace the the cables that the insulator can sustain high temperature or insert the heat shrink tubes to the original cables. The temperature sensor is situated under the black plastic cover with a mercedes logo in front of the engine.

 

[megabyting]

incorrect coolant sensor reading will cause excessive fuel consumption, better to sort it out quickly.

 

[aadil]

my c200 w202 (1999) is having the same problems as posted by gb metallic on 05-05-2010.How did he cure the problem

 

[Grey Area]

So you're having problems with your fan and a/c or one of the two? Some more specific info please.

 

[gb metallic]

Sorrry about the late reply. I did solve the problem. I had waste money on the fan controller but it was the coding of the EIS ignition switch module that had the car not recognised as a W202 saloon or Right Hand Drive, which makes you believe its the fan controller making the fan run at full speed.

I had buy Star MB C4. In the section KI. Had find it under Variant coding; which was not set as you have option of T202 estate and W202 saloon. and also left hand and right hand drive. If these are not set correctly it would make the fan run at full speed. Very weird, but true.