98 SLK230K Coolant fan not working.

[GadgetBoy]

I'm reviving this car and working through it's surprisingly few problems.

In trying to get the A/C working Carsoft threw up a coolant fan error which backed up my suspicions that it wasn't working with the temperature gauge getting highish a few times and the coolant light flickering.

I've checked all the fuses and I have power to the control module on the inner wing. I've jumped this 12V across to the fan terminals and off it goes. I've tried a 2nd control module and it doesn't seem to want to drive the fan either.

So either I've got 2 duff control modules or we're not getting the appropriate signalling.

Does anyone have a wiring diagram or diagnostic procedure for this circuit?

 

[Dec]

What about the temperature sensor?

Dec

“Remove the solenoid. I replaced its mounting bolts back into the block so as to not loose them. At this point, disconnect the Camshaft adjuster and the temperature sensor.”

Picture source… 1998 Mercedes SLK 230 Head gasket removal & replacement

 

[GadgetBoy]

Surely if the temperature sensor was faulty I wouldn't have a temperature gauge and the flickering warning light?

 

[Dec]

Its one of the elements that determines when the fan comes on = Sensor-Relay-Fan motor.

Would it be worth changeling it?

Dec

 

[GadgetBoy]

There's no relay, it's a PWM Speed Controller much as you would get in a remote control car.

Anyways, CTS output as expected.

 

[Dec]

There is a relay? / control module? like the below picture of a W202, it would seem that the SLK has one too.
Could that have something to do with the problem?

Dec

[YOUTUBE HD]AoUMr6084yo[/YOUTUBE HD]

[YOUTUBE HD]M6u0jaTHbTw[/YOUTUBE HD]

[YOUTUBE HD]Ytbx5MHfWeI [/YOUTUBE HD]

The video above doesn't seem to work.
Try... https://www.youtube.com/watch?v=Ytbx5MHfWeI

 

[GadgetBoy]

It is labelled as a relay but it isn't, it's a speed controller. When have you ever seen a relay with a dirty great heat sink?

 

[GadgetBoy]

Actually those videos are quite useful.

I'm waiting for my mate to return my scope and then I can check the control inputs, if they're fine then that's some very simple circuitry inside that and easily repairable.

The input should be a variable width pulse depending on what speed is required. PWM - Pulse Width Modulation.

 

[Dec]

The presenter in the video is trying to be helpful, he may have solved your problem so don’t be knocking the chap.

Dec

 

[GadgetBoy]

Fair point. Edited.

 

[Dec]

I always thought that contained a relay for the fan, thanks to the Texan I now know differently, let us know how you get on as I’m curious to know the solutions to your particular problems as I may encounter the same fault in my car in the future.

Dec

 

[GadgetBoy]

I certainly will. It's got me stumped because so far everything I've tested has been fine.

I am a bit blind without a wiring diagram though, having to trace everything.

 

[markmifsud]

The wiring diagram will not be of much use, it just shows:
N76 Engine and air conditioning electric suction fan control module
connects to
U150
Connects through Connection block X54/7
Connects to Aux Fan M4/3

 

[GadgetBoy]

Thanks. It's a detective job then! Oh joy!

 

[GadgetBoy]

Detective time tomorrow!

 

[BandyAndy]

How about having a read through this thread, it may be able to help you out

Can AC compressor and aux fan run at the same time? - Mercedes-Benz Forum

 

[GadgetBoy]

Here's what I know.

The fan works if you supply it with 12V.
There's power to the speed controller.
The coolant temperature sensor works as it should.
The A/C clutch is working.
All the fuses are fine.

So all the evidence is pointing to the fan speed controller not getting any signal or not processing any signal its getting correctly.

Scope to monitor the PWM input to the speed controller.
Signal/function generator to spoof a PWM signal.

Will report tomorrow night.

 

[GadgetBoy]

It's been a while but .....

All is now working as it should yay!

Turns out there were two problems and although they aren't connected I made two fundamental errors.

Error 1. Assuming that because the air conditioning had just been recharged it was working.

Error 2. Assuming the air conditioning was working.

Subtle difference there!

When I originally discovered the coolant fan wasn't working I started down a road which would ultimately lead to a dead end. I knew that when the airco was running the coolant fan would also run so I started using this as my test for was the fan working. As I said above I assumed the airco was working - I shouldn't have - it wasn't so I was beating a dead haddock from the get go.

CarSoft didn't help either. Now I will say it didn't do anything wrong, it was just misleading. It would constantly give the error B1421 Check operation of auxiliary fan so I assumed this was why the airco wasn't working when I eventually discovered the airco was in fact dead.

Long story short, I bought an eBay speed controller and fitted that thinking that this would be my panacea and of course my incorrect assumptions lead me to believe this was also faulty.

I gave up and brought the car to my local Indie (Creevy Autos) for a Star session. Now Star does something CarSoft doesn't, it allows you to control the fan from the computer and lo and behold it ran - speed range all fine. Woo hoo!

Being at the limit of my knowledge said Indie and I agreed it needed an auto spark to get to the bottom of the problems so the car was booked into Greenaways. They immediately diagnosed the airco was sicky bad due to a disintegrating condenser. New condenser, re-gas and everything is working as it should. One last test - try old speed controller and fan dead again. Original problem finally solved!

 

[Dec]

Thanks for the feedback, good result then, did you discover what was wrong with the old speed controller?

Dec

 

[GadgetBoy]

No. I replaced the capacitors but no joy. There isn't much to them but I haven't tried tracing it yet. If I get time someday I might have a probe around.