Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2008 Subaru Impreza - Pain in the mass airflow sensor

I’ve had my 08 Impreza for a little over a year now, and have to replace the mass air flow sensor twice, and still keep having recurring problems. The code is P0172 every time, and we’ve been cleaning the newest sensor, a Denso bought in June this year, at least twice so far. I know rhere has to be an underlying cause for this to keep happening, and it’s getting really tiresome at this point. Any suggestions for what keeps causing this, something fixable hopefully?

P0172 Causes

  • Dirty or faulty [Mass Air Flow (MAF)]
  • Faulty oxygen sensor
  • Leaky fuel injectors allowing too much fuel into the combustion cylinders
  • Worn spark plugs
  • Stuck fuel pressure regulator
  • Faulty coolant temperature sensor
  • Faulty coolant thermostat

Since the MAF has been replaced twice and the code keeps returning, then the MAF is probably not the problem. One of these other sensors or parts is at fault. I don’t know who is doing the work but you should stop using them!

1 Like

P0172 is a fuel trim “rich” code

There are many potential causes, such as a severely restricted engine air filter, high fuel pressure, and the things @Mustangman already mentioned, but others as well

Replacing the MAF sensor sounds like somebody who has weak diagnostic skills is working on the vehicle

Go somewhere else


@Mustangman, Thank you! I haven’t actually been to a garage or a mechanic for this - we’ve been working on dealing with this ourselves. I recently had the oxygen sensor (BANK 1) replaced, and we have replaced the air filter. Will try the spark plugs next, then go from there to look at the other items you’ve suggested. Thank you so much for your help!

@db4690, Thank you! What would the “others as well” be? Just curious - open to suggestions since it’s become obvious that the MAF Sensor route is only a temporary bandaid fix. Thanks!