DIY: Gen 4 MAF (Mass Air Flow) Sensor Cleaning - Subaru Outback - Subaru Outback Forums

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Old 04-06-2013, 05:51 PM   #1 (permalink)
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Default DIY: Gen 4 MAF (Mass Air Flow) Sensor Cleaning

The Mass Air Flow (MAF) Sensor measures the flowrate of air through the air intake before reaching the engine. Since the density of air changes with temperature and pressure (due to ambient temperature, altitude), the ECU needs this information to provide the correct fuel mass to the engine.

So WHY is it important to clean the MAF Sensor? Over time, dust and oil particles will stick to the hot wire (what measures the flowrate of air) and essentially "bake" on and distort the measurement. The result can be rough idling, poor acceleration and engine starting, and overall worse gas mileage. Cleaning the MAF Sensor can remedy or avoid these symptoms. Also, you can avoid the costly replacement of the MAF Sensor by cleaning it regularly. I usually clean mine at every oil change interval - doing it is quick, easy, and cheap.

Equipment needed: CRC Mass Air Flow Sensor Cleaner (available at any auto parts store, costs about $7)
Tools needed: Philips head screwdriver
Level of difficulty: Low
Time needed: 5 minutes

CRC Mass Air Flow Sensor Cleaner:

Open the hood and locate the MAF Sensor, on top of the air duct between the air filter and throttle body, circled in blue here:

Disconnect the wiring harness, remove the two screws and carefully pull the MAF Sensor from the housing. Then, spray the MAF Sensor with the CRC. The hot wire (circled in blue below) is the important part you need to clean, but I usually just douse the entire piece with CRC to remove all particulates. Just be careful NOT to touch the wires - just hold it by the part where the wiring harness was connected as shown below. The cleaner will evaporate in a few seconds; let it completely dry before reinstalling (carefully reinsert the sensor, attach two screws and connect wiring harness). And you're done.
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Old 04-06-2013, 08:18 PM   #2 (permalink)
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How much contamination was found on the wire? Just curious, because a hot-wire sensor is supposed to go through a self cleaning cycle on start-up.
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Old 04-07-2013, 08:04 AM   #3 (permalink)
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^ If you clean the wire often enough any buildup of contaminants probably won't be visible to the naked eye, but there could still be microscopic particles on the wire.

A hot wire burn-off cleaning circuit is used on some sensors, but as far as I know the Subaru MAF Sensor does not have this feature.

Anyway, this DIY is so cheap and easy it's safer to do it every 3k or 7k miles than have to replace a burnt out MAF Sensor (about $150).
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Old 04-07-2013, 09:25 AM   #4 (permalink)
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I'd like to add a cautionary note- improper cleaning or handling during cleaning can harm the MAF. Cleaning it more frequently adds more handling, more chances to screw up an expensive part.

Given that many drivers will plow through 100k miles without any MAF related symptoms, it is worth balancing the performance of a perfectly clean sensor against the risk of overhandling the parts.
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Old 04-07-2013, 10:28 AM   #5 (permalink)
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^ That's fair; as with any self-performed maintenance there is always the chance of doing more harm than good. That being said, the OB's MAF Sensor is one of the "safest" to clean compared to other cars I've worked on in that the hot wire is mostly protected by plastic. One would have to TRY to touch the wire in order to make contact.

And, although the MAF Sensor may not fully break over XXXX miles, owners can still be unknowing victims of poor acceleration and worse gas mileage due to a dirty MAF Sensor.
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Old 04-07-2013, 10:55 AM   #6 (permalink)
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The Bosch-style MAF sensor originally used on EJ/EG engines was self-cleaning and I don't recall any discussions about cleaning those. If the current type isn't self cleaning, that's another small step in the process of cheapening up and general toyotazation.
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Old 04-07-2013, 05:54 PM   #7 (permalink)
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The Gen 4 OB's MAF Sensor is made by Denso, and from my research I have not seen anything that leads me to believe the Outback's MAF Sensor is self cleaning. Even if it was, I would still clean it regularly to ensure the entire part was clean and not just the hot wire.

My BMW did not have a self cleaning MAF Sensor, so I would be surprised if Subaru sprung for it on their lineup.
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Old 04-07-2013, 06:27 PM   #8 (permalink)
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I clean the MAF sensors in all my vehicles every 18 months. Pouring rubbing alcohol over the 3 small delicate elements also works (along with electronic parts cleaner).
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Old 04-07-2013, 09:37 PM   #9 (permalink)
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The original EJ MAFs are self cleaning as I said. I will totally believe that the current style (1999 on) is not. MAF cleaning threads didn't really start until the turn of the century. As to BMW MAFs, I don't really know, but it seems there's no clear agreement:
http://www.m5board.com/vbulletin/m5-...tml#post554109
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