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BMW Mass Air Flow (MAF) Sensor Location and Cleaning

April 13, 2011

This answer is applicable for many BMWs in addition to the one listed below.

Q
car year: 1997
car model: 528i
Hi, I was wondering where is the Mass Air Flow Sensor in my 97′ 528i and how to clean it properly.

A
BMW started using Mass Air Flow sensors (MAF) in the early ’90s on most models (note that MINIs and some latest model BMWs do not use this system and do not have MAF units).  Prior to this, the Bosch Motronic and L-Jetronic electronic fuel injection systems used an electro-mechanical Air Flow Meter.  While the Air Flow Meter measured the airflow with a swinging flap that was pushed open by the engine’s intake airflow, the newer MAF units use an electrically heated wire or metal film that is  cooled by the incoming airflow.  The cooling changes the resistance of the sensor wire or film and, hence, the voltage that can flow through the wire or film.  The Engine Control Unit (ECU) measures this change and determines the mass of the airflow into the engine.

As the MAF hot wire or film ages it becomes dirty as contaminants in the air are deposited on the wire or film.  When this happens, the sensor becomes less responsive and losses accuracy.  This leads to a degradation of engine efficiency, since the ECU is receiving inaccurate information.  Bavarian Autosport fully recommends periodic cleaning of the MAF sensor wire or film.  Once per year is adequate for most applications.

On most BMWs, the MAF is located directly behind the air filter box.  Typically it is a cylindrical unit that is connected directly to the filter box.  Some later models have MAF sensors that incorporate just the sensor itself (without the cylindrical airflow housing), which is mounted into the air filter box or in another location withing the intake system.  To clean the MAF, simply remove it and liberally spray the hot wire or film with a specific MAF cleaner.  We use and recommend the CRC (brand) Mass Airflow Sensor Cleaner.

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