Mercedes-Benz W204 cooling fan running at full speed
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Mercedes-Benz W204: why does the cooling fan run at full speed?
The fan goes to full speed when its control signal is missing. The cause can be a faulty A/C pressure switch or pressure sensor, a chafed or corroded wire, or a fault in the fan connector. The fan can run even when the A/C is not on.
Mercedes-Benz W204: do I have to replace the fan right away when it runs at full speed?
No. The fault is first confirmed by measuring, and the fan part number is checked. Unnecessary replacements have been made when the cause was in the control signal, such as the A/C pressure switch or the wiring. Coolant that has got onto the fan's electronics can also cause a malfunction.
Mercedes-Benz W204: can a running cooling fan drain the battery?
Yes. The fan draws a lot of current, so if it keeps running with the ignition off, the battery can go flat. The cause should be found quickly by measuring the control signal and the wiring.
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