What is the reason for BMW fan output stage detecting an open load circuit?
3 Answers
BMW fan output stage detects an open load circuit due to reasons such as coil overheating damage or absence of 220V AC input, as detailed below: Coil overheating damage: Prolonged use of the fan causes excessive dust accumulation, increasing the friction coefficient between the rotor and bearings, leading to rotor obstruction or even seizing, resulting in coil overheating damage. Solution: After powering off, open the rear cover of the fan, add a few drops of lubricating oil to the bearing sleeves at both ends of the rotor, and rotate the blades while adding oil until they move freely, thereby eliminating the blower fault. No 220V AC input: This may be due to the absence of 220V AC input or coil damage. Solution: Disconnect the power, separate the two lead wires of the fan from the power supply connection points, leaving them suspended. Turn on the power and carefully measure both ends of the power line with a test pen. If one end lights up and the other does not, it indicates the power input is normal, and the issue might be with the fan coil. If both ends do not light up, it suggests a problem with the power input line.
I've been repairing cars for many years, and encountering BMW fan output stage alarms indicating a broken load circuit is quite common. Simply put, it means the fan isn't receiving power. Possible causes include damaged or aged wiring, loose or corroded connectors, a shorted or burnt-out fan motor, a blown fuse protecting the circuit, or a faulty control module sending incorrect signals. Wires in the engine compartment are prone to wear and breakage due to high temperatures and vibrations, and loose connectors can lead to poor contact—these are common findings during routine repairs. Once the circuit is broken, the fan stops immediately, and without engine cooling, overheating and severe engine damage can occur. During inspection, first use a multimeter to check the fuse and circuit continuity to locate and repair the break or replace parts. Never attempt DIY fixes—take it to a professional 4S shop or a reliable repair shop where diagnostic tools can accurately pinpoint the issue, saving time and effort, and preventing your car from turning into scrap metal.
As a car enthusiast, I've studied BMW's fan system. The output stage detecting a load open-circuit essentially means the current path is broken and the fan stops. Possible causes include the fan control module detecting no load current, with root causes involving aged/broken wiring, oxidized/loose connector terminals, burnt/open coils in the fan motor, or blown fuses. For example, poor circuit contact can increase resistance and interrupt power supply. Interestingly, it can warn of potential risks - if the fan doesn't cool the radiator, rising temperatures may trigger engine warnings or even stalling, ruining safe driving. For diagnosis, use an OBD scanner to read error codes for the source, check fuse box status and clean connector dust - sometimes this solves it. If hardware is damaged, replace it promptly to prevent minor issues becoming major faults.
