Originally Posted by
jimcross
Could this module cause the cooling fan to run at very high speed? I determined that it's not the fan control module. Also, the AC doesn't blow cold air. Can this and the pcm be related?
The fan doesn't start right up high when cold starting the 1st time. It starts running very high after about 2 minutes from a cold start.
Yes, the system is very simple.
The ECU sends "tickle pulses" (my term) continuously, to the FCM. The FCM responds, as long as this continues, all is fine.
If the FCM fails to get the pulses, it goes into "Emergency Mode" and runs the fan at high speed.
If the ECU fails to get the pulses back from the FCM, it lights the "Low coolant light".
In order to run the fan at various speeds, the ECU sends wider pulses, the wider the pulse, the faster the FCM will spin the fan.
That's all there is to it, so a fan that runs at high speed is either a bad FCM, a bad ECU or the wire running between the two is open.
I found a site (Flagship One) that will send me a module matched to my VIN. What's your thoughts?
I've been on here 12 years, never heard of them. I'd go to Josh Chase at the Mercedes Swap Shop in California. Josh is on Facebook and here on the forum, I will message him about this thread.