I noticed my L322 started doing this around this summer. Every time I open a door or trunk a fan starts running, even though the car itself is not running nor key in the ignition. The fan runs for around 30secs to few mins. I've located the sound, it's coming from the FBH.

Also my FBH does not seem to work, which it did last winter, no problem. Iidtool gives few codes for FBH, 0x0202 combustion air fan - short circuit to ground and 0x0204 combustion air fan - open circuit or short circuit to battery. The fuse is fine, and the FBH itself will react when attempting to start it via Altox app. It starts the same fan that fires up when opening door/trunk, runs few minutes and then stops.

I suspect that FBH could use a good cleaning internally regarding the combustion fan, but I wonder if the fan running when opening door is related/part of the same problem or a different one completely. Hvac does not give any codes with Iidtool. Also it's -07 so I can't do the forced start manouver with Iidtool, since its only for 2010 and later.

Any ideas?

Well, the door status is broadcast on the K-Bus, which is the one the FBH is connected to, it sounds like the controller is taking the door status (and likely other messages as well) as the 'startup' message. The fan runs initially before any combustion is initiated as a self test (which it is failing) so there won't be any other DTC's.
I'd be having a look at the control board, checking for moisture ingress or resistor rot, you never know, just disconnecting it for a while might cause a reset!
Possibly you might need a new controller as the fan is triggered solely by that, if there are erroneous DTC's being set and strange activity, then it may well be that the control board has an unrecoverable defect.

Thank you for your reply. Is the control board under the battery tray, same place as the FBH? Might aswell take a peek.

The control board is part of the FBH - it's behind the plastic moulding with the electrical connectors on it - which itself has a plastic cover over it.

Not my photo - the white-ish blobs have been known to cause 'resistor rot' leading to various faults, the SMT resistors can be replaced relatively easily if you are handy enough with a small soldering iron, there are places (I think there is one in Norway) that can fully repair your existing board, not just cure the potential resistor issue - be careful with replacement boards, there are many different versions. You need the specific LR version.

I occasionally have the same problem

The conclusion I came to was that the FBH had come on (timer or remote fob), but shut down early due to low battery.
Then when car wakes up again, the FBH comes back to life to complete cycle….so you hear the fan start up.

Time for new battery….

Phoenix wrote:

The control board is part of the FBH - it's behind the plastic moulding with the electrical connectors on it - which itself has a plastic cover over it.

Not my photo - the white-ish blobs have been known to cause 'resistor rot' leading to various faults, the SMT resistors can be replaced relatively easily if you are handy enough with a small soldering iron, there are places (I think there is one in Norway) that can fully repair your existing board, not just cure the potential resistor issue - be careful with replacement boards, there are many different versions. You need the specific LR version.

I appreciate your answers

Ei hätää!

I used to spend a fair bit of time in Finland a few years ago, I know the value of pre-heating (and a good sauna!).

Rambles wrote:

I occasionally have the same problem

The conclusion I came to was that the FBH had come on (timer or remote fob), but shut down early due to low battery.
Then when car wakes up again, the FBH comes back to life to complete cycle….so you hear the fan start up.

Time for new battery….