Radiator Fan

[design guru]

I have a W202 C240 1998. I was running fine until the water pump began leaking so I replaced the water pump successfully and now when I start the car the radiator fan in front of the engine runs at full speed continuously.

I was not doing this before, the only issue I did have after replacing the pump was the battery had gone flat after I left the boot open whilst changing the part and the interior light must have drained the battery and it had not been run for 2 days.

I charged the battery fully but the fan still runs at full speed as soon as the car is started. The engine is cold. Anybody have similar issue and found the cause?

 

[mersum1es]

Check all fuses and battery leads, full speed fan means either missing- or undervoltage of ecu, faulty fan controller or faulty temp sensor. Since you car had undervoltage, ecu may have been interrupted by loading all info, and now it cannot recover it and is missing part of car data. It usually can be restored via SDS.

 

[design guru]

I checked All the wires and fuses which turned out to be fine but I did eventually find the problem, it seems the sensor that is on the front of the engine block, the plastic plug holder had bent causing one of the contacts to break so the sensor was not operating causing the fan to remain on as a fail safe.

I have ordered a new part and in the meantime removed the plug for the fan as the car is only used for trips to the shops now and then so it can be driven without the fan running at full speed or cause the fan to burn out. Will update when part is fitted to confirm this has solved the issue.

 

[design guru]

Well the sensor was the problem thankfully. Only cost £6, only downside was the old one was stuck in there and ended up removing it in small chunks but got it out. New sensor fitted and the fan does not run constantly when the car is started.

Thanks to Mersum1es for a run down on possible causes. A great help.