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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:

T20 Torx driver

Applicable Models:

Saab 9-3 2.0T (2006-07)

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

Saab 93 digital engine management systems use a hot-wire 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 are thin metal wire resistors, which are maintained at a constant temperature via electrical current from the ECM (engine control module). As ambient intake air flows over the wires, it is cooled down and therefore additional current is needed to maintain its constant temperature. The ECM 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 wire monitors heat-loss to the passing air, it automatically adjusts for the increased volume (= lower density) of the incoming air.

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. If you have a rich fuel trim fault at idle and lean when driving, this indicates a dirty wire. You can clean the wire using mass air flow cleaner. See the last step in this article for tips on cleaning.

In this tech article I will show you how to replace the mass air flow sensor on Saab 93 models with 2.0t engines.

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 right side of the engine.
Figure 1

The mass air flow sensor (red arrow) is located at the air filter housing outlet, on the right 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.

Disconnect the mass air flow electrical connector (red arrow).
Figure 2

Disconnect the mass air flow electrical connector (red arrow). Slide the lock toward the firewall. Then pull the connector straight off.

Working at the mass air flow sensor, remove the two T20 Torx screws (red arrows).
Figure 3

Working at the mass air flow sensor, remove the two T20 Torx screws (red arrows).

Remove the sensor from the intake air housing lid (red arrow).
Figure 4

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.

Saab 93 digital engine management systems use a hot-wire (red arrow) mass air flow sensor, installed between the air filter housing and the intake manifold, to monitor air flow into the engine intake.
Figure 5

Saab 93 digital engine management systems use a hot-wire (red arrow) 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 are thin metal wire resistors, which are maintained at a constant temperature via electrical current from the ECM (engine control module). As ambient intake air flows over the wires, it is cooled down and therefore additional current is needed to maintain its constant temperature. The ECM 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 wire monitors heat-loss to the passing air, it automatically adjusts for the increased volume (= lower density) of the incoming air. Note the lower wire, it is covered in road debris (red arrow). This can be cleaned and sometimes will remedy your fuel trim fault.

Using mass air flow cleaner, spray (red arrow) the wires clean.
Figure 6

Using mass air flow cleaner, spray (red arrow) the wires clean. Then dry them with low pressure compressed air. Be careful. Too much pressure can damage the sensor. Once clean and dry, reinstall the sensor. Reset the fault code and test drive to check if the fuel trim fault is remedied.






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