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Marty, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 54958
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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I have just acquired a class c240 and am having a problem which

Customer Question

I have just acquired a class c240 and am having a problem which my garage seems unable to solve. When I start the car the cooling fan revs at max revs and seems uncontrolled. I have spent about £550 it seems needlessly recharging the refrigerant and replacing the fan and control assembly to no avail. Please can you advise me
Submitted: 4 years ago.
Category: Mercedes
Expert:  Marty replied 4 years ago.
Hi, and welcome. My name is Marty. This problem is usually caused by a faulty front signal acquisition module (SAM) or a fault in the engine control module. Both of these modules affect the operation of the suction fan. A fault in either module will cause the suction fan to default to high speed. Either the front SAM or the engine control module is not properly coded or one of the modules is bad. The mechanic needs to check the version coding of both the front SAM and the engine control module to be sure it is properly coded for the suction fan. A Mercedes factory level scan tool is required for this. Fuse 51 also need to be checked to be sure it is supplying power to the suction fan on the black/white wire. Please let me know if you have any questions.