BMW Diagnostics: Low Airflow After Cabin Filter Replacement

BMW Diagnostics: Low Airflow After Cabin Filter Replacement


  • F97 X3 M 
  • F98 X4 M
  • G01 X3
  • G02 X4
  • G20 3-Series


After replacing the microfilter during a previous service, 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 fresh air flap can be over-driven (pushed past its normal end stop) when the microfilter is replaced. The regular opening and closing of the fresh air flap can no longer be guaranteed. To prevent this situation, when inserting the microfilter, it is essential to ensure that the air recirculation function on the air conditioning control panel is activated and fresh air (the top flap of 3) is in the closed position.


To rectify this concern, access the fresh air flap and determine if it can be returned to its normal position.


1. Activate the air recirculation function by pressing the recirculation button on the climate control panel(Recirculation mode, circled), LED ON. This will close the top fresh air flap leaving the bottom two recirculation flaps open. NOTE: It is the top flap which is in danger of being damaged during microfilter service.

2. This can be confirmed in the Central Information Display (CID) in the Climate Control Menu (MENU A/C) underAIR QUALITY. Ensure the flap is set to Air recirculation so the top flap (fresh air inlet) sits flat and does not interfere with microfilter removal.

3. Dismantle the microfilter

4. Remove the ventilation system blower motor.

5. Check correct position of the fresh air flap through the blower motor opening, or using a borescope from the microfilter opening. NOTE: This flap is the top of three flaps. Activate and deactivate the fresh air/air recirculation function on the air conditioning control panel or CID menu and observe whether the functionality of the flap is OK. If the flap system is OK, the vehicle can be reassembled.

6. If the flap system is not OK, try to correct the flap by hand. See direction of arrow. 

7. Once moved back past the end point, the flap may not function properly. 

  • After moving flap manually, use the test plan ABL to re-initialize/address the stepper motor position.
  • Allow vehicle to enter sleep mode after running the test plan prior to testing flap positioning
  • If still not operational, then you may have to remove the stepper motor to check for damage. Once repaired, run the ABL to initialize the stepper motors and allow the vehicle to enter sleep mode before testing.

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