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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:

$200

Talent:

**

Tools:

Flathead screwdriver, 10mm socket

Applicable Models:

Volvo V70 (1998-01)
Volvo V70 2.4T (2001)
Volvo V70 AWD (1998-99)
Volvo V70 GLT (1998-00)
Volvo V70 GLT SE (2000)
Volvo V70 R (1998)
Volvo V70 R AWD (1999-00)
Volvo V70 T5 (1998-01)
Volvo V70 X/C (2001)
Volvo V70 X/C AWD (1998-00)
Volvo V70 X/C AWD SE (2000)

Parts Required:

Mass air flow sensor, engine air filter

Hot Tip:

Work with a cool engine, and clear engine fault codes when done

Performance Gain:

Car will run well

Complementary Modification:

Replace engine air filter, inspect intake air ducts for cracks

Volvo V70 digital engine management (DME) 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 is a small hot wire resistor, which is maintained at a constant temperature via electrical current from the ECM. Unlike other hot wire types, the mass air flow sensor in the Denso system uses a hot wire that has a ceramic casing. This eliminates the need for a clean burn function. As ambient intake air flows over the film, 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 film 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.

The mass air flow (MAF) sensor gauges the air mass sucked into the engine. It continuously transmits signals to the engine control module (ECM) about the mass of the intake air. This data is used by the engine control module (ECM) to calculate the injection period, ignition timing and engine load.

The transmission control module (TCM) also uses this data for its gear shift calculations. This data is transmitted to the transmission control module (TCM) from the engine control module (ECM) via the high speed side of the Controller area network (CAN).

The mass air flow (MAF) sensor is supplied with battery voltage by the system relay and is grounded in the engine control module (ECM). The signal from the sensor is analog and varies between 0.5-4.5 V depending on the air mass. Low air flow (low mass) results in low voltage. High air flow (high mass) gives high voltage.

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 remote key from the ignition.

The mass air flow sensor is located in the air filter housing outlet (red arrow).
Figure 1

The mass air flow sensor is located in the air filter housing outlet (red arrow).

Disconnect the mass air flow sensor electrical connector by pressing the release tab and pulling the connector straight out of the sensor.
Figure 2

Disconnect the mass air flow sensor electrical connector by pressing the release tab and pulling the connector straight out of the sensor.

Loosen the intake air duct hose clamp (red arrow).
Figure 3

Loosen the intake air duct hose clamp (red arrow).

Pull the intake air duct off the mass air flow sensor.
Figure 4

Pull the intake air duct off the mass air flow sensor.

Working at the mass air flow sensor, remove the two 10mm fasteners (red arrow).
Figure 5

Working at the mass air flow sensor, remove the two 10mm fasteners (red arrow).

Remove the mass air flow sensor by pulling it straight out of the intake air housing (red arrow).
Figure 6

Remove the mass air flow sensor by pulling it straight out of the intake air housing (red arrow).

Install a new mass air flow sensor into the air filter housing.
Figure 7

Install a new mass air flow sensor into the air filter housing. If the seal (green arrow) gives you a hard time going in, apply a small amount of dish soap to it. It will slide right in and the soap will not damage the seal. 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: Fri 12/9/2016 02:48:14 AM