Fan Power Stage repair service
The power stage that manages the power for the coolant fans in a 928S4, GT, and GTS is located on top of the front bumper, very close the the refrigerant filter and high pressure port, right hand side so on the passenger side for EU. The power stage part number is 928.618.421.00
Please order your Fan Power stage repair in our webshop.
The fan power stage gets signals from the fan controller 928.618.418.00 which is located besides the passenger seat under a cover (in front of the audio power amp).
The Fan controller has the task of evaluating signals from various sensors and using that to send a signal to the Fan Power Stage. The power stage has the task to efficiently manage the power that goes to the fans without heating up too much. A problem with either fan is sensed and sent back to the fan controller module. The controller module then turns one fan to max power to compensate for the (other) failed fan unit. The typical behavior is easy to spot: the fan runs very VERY loud when the fan is activated.
Well, the system is pretty well made, it utilizes a Pulse Width Modulation to manage fan rpm as efficiently as possible. It works great until it breaks down, mostly due to age.
Typical symptoms are:
- Total lack of power to turn on the fans (presuming 12v is available on the round connector of the power amp, and ground connection is ok)
- One fan runs max as soon as the battery is connected
- Both fans run max as soon as the battery is connected
- One fan runs max and the other is silent. Sometimes suddenly both run, or the problem moves from one fan to the other (so running fan gets silent and failed fan suddenly runs full power.
- One fan is silent, the other fan runs at max rpm, and this rpm fluctuates in a regular 10 sec cycle where the controller samples the non-running fan.
It turns out that it is not at all easy to identify the root cause that makes the fan power stage act in emergency mode.
Possible causes are: broken fuse, bad fuse contact (burned socket), bad controller module, bad contacts on power stage or fans, bad ground contact for fans... and of course a faulty power stage.
We worked for almost two years to find proper solutions to all of the problems that make the fan power stage fail. And we are confident we can now repair these boxes so that the system works reliable again.
The repair consists of finding the broken part(s), replacing and testing. Since the repair is not a simple "swap-a-component" we need to confirm proper operation by a test drive for a while. So we only offer a swap service with a core refund. Every repaired power stage is repaired professionally, sealed so that water can not enter anymore, and new rubber o-rings placed on the main connector. Repair carries a one year warranty.
