Recently, BMW issued a TSB on cabin air filter replacement for some 3 Series and 4 Series models. This TSB applies to vehicles with automatic temperature control HVAC systems where the recirculation door is close to the cabin air filter housing.
TSB SI B64 03 21 describes a situation where after replacing the cabin air filter, the customer notices that the ventilation system airflow rate is noticeably less. This leads to perceived lower cooling power.
The customer may also notice that external odors enter the vehicle. The cause of the complaint is that the fresh air flap can be hit by the new filter and pushed past its normal end stop. The regular opening and closing of the fresh air flap can no longer be guaranteed. To prevent this situation, when inserting the cabin air filter, it’s essential to ensure that the air recirculation function on the air conditioning control panel is activated and in the closed position.
There are two things to learn from this TSB when replacing a cabin air filter on any late model vehicle.
First, if you’re unsure about the replacement procedure for a vehicle, look at the service information and look for any TSBs that might apply.
Second, many vehicles have position sensors on the doors and flaps. If a flap is forced open or closed, you might have to recalibrate the door position with a scan tool.
So the next time you service a cabin air filter on a vehicle you are seeing for the first time, take your time and never force a filter into a housing.
This video is sponsored by FRAM.