Mercedes-Benz W202 electric fan runs constantly or does not run
Mercedes-Benz W202 electric fan runs at full speed all the time. What is the fault?
The most common cause is the fan control box, whose regulator part can overheat and burn out. Replacing the control box has most often fixed the fault. Other suspects are oxidised connectors and a stuck temperature sensor.
Where is the Mercedes-Benz W202 fan control box and how does its failure show?
The box is on the driver's side inside the front wing, in front of the left front wheel. The fault shows as the fan running continuously, often with the coolant warning light on. An oxidised or overheated connector can melt onto the box.
How do I find the right control box, and is a used box worth it?
There are several box models, and the right one can be found at a parts shop with the registration number. The part numbers of the diesel and petrol boxes differ: diesel A 020 545 15 32, petrol A 018 545 99 32. A faulty box can damage the control unit, so worn ones are not worth trying.
Why does the Mercedes-Benz W202 electric fan not run although the engine overheats?
The fan starts based on information from the temperature sensor, so check the sensor and its connector as well as the control box connector. You can also check whether the fan turns by hand and give it direct power for a test.