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Mass Air Flow Sensor Replacement
 
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Pelican Technical Article:

Mass Air Flow Sensor Replacement

Nick Czerula

Time:

1 hour1 hr

Tab:

$500

Talent:

**

Tools:

T25 Torx driver

Applicable Models:

BMW Z4 Convertible (2003-06)
BMW Z4 Coupe (2006)

Parts Required:

Mass air flow sensor, engine air filter

Hot Tip:

Work with a cool engine. Clear engine fault codes when done

Performance Gain:

Car will run well

Complementary Modification:

Replace engine air filter, inspect intake air ducts for cracks

BMW Z4 digital engine management (DME) systems use a hot-film mass air flow sensor, installed between the air filter housing and the intake manifold, to monitor air flow into the engine intake. Inside the sensor, there is a thin metal film, which is maintained at a constant temperature via electrical current from the DME. As ambient intake air flows over the film, it is cooled down and therefore additional current is needed to maintain its constant temperature. The DME monitors this additional current to determine the mass of the incoming air and to adjust fuel supply accordingly. Note that as the temperature of ambient air increases its volume expands. Since the air flow sensor hot film monitors heat-loss to the passing air, it automatically adjusts for the increased volume (= lower density) of the incoming air. The HFM6 style sensor sends a digital mass air flow and temperature signal to the DME. For more information, see our tech article on mass air flow sensor testing.

Mass air flow sensors accuracy skews over time and can lead to fault codes or drivability problems. When replacing, inspect the plastic intake air ducts for cracks or dry rot. If the intake air ducts are faulty, replace them first and see if the problem you are having is remedied. An un-metered air leak downstream of the mass air flow sensor will set codes similar to a faulty mass air flow sensor. When you suspect a mass air flow sensor as the culprit for setting a fuel trim fault code, check when the fault code was set. You can do this using OBD II freeze frame data. Normally, a vacuum leak would set a fuel trim fault code at idle or very low engine RPMs. A mass air flow meter would usually set a fault code when you are driving, or at a higher RPM. You can check your fault code freeze frame data using an OBD II scan tool, similar to how you would check for fault codes.

In this tech article I will show you how to replace the mass air flow sensor on BMW Z4 models with S54 engines. M54 engine equipped models are similar.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Turn the engine OFF and remove the key.

The mass air flow sensor (red arrow) is located at the air filter housing outlet on the left side of the engine.
Figure 1

The mass air flow sensor (red arrow) is located at the air filter housing outlet on the left side of the engine. Fresh air is drawn in through the bottom of the intake air housing, through the air filter and measured by the mass air flow sensor.

Start by removing the plastic line clipped to the intake air housing.
Figure 2

Start by removing the plastic line clipped to the intake air housing. Pull the line (red arrow) straight up to remove it from the mounts.

Then, disconnect the mass air flow sensor electrical connector by squeezing the release tabs and pulling it straight off.
Figure 3

Then, disconnect the mass air flow sensor electrical connector by squeezing the release tabs and pulling it straight off.

Working at the mass air flow sensor, remove the two T25 Torx screws (red arrows).
Figure 4

Working at the mass air flow sensor, remove the two T25 Torx screws (red arrows).

Remove the sensor from the intake air housing lid (red arrow).
Figure 5

Remove the sensor from the intake air housing lid (red arrow). If stuck, use a small flathead screwdriver to gently lever it out of the lid. Install a new mass air flow sensor into the air filter housing. If the O-ring gives you a hard time going in, apply a small amount of dish soap to the O-ring. It will slide right in and the soap will not damage the O-ring. Check the vehicle for fault codes. See our tech article on reading and clearing fault codes. Then test drive the vehicle and confirm that the engine runs well.




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Page last updated: Wed 12/7/2016 02:56:12 AM