hi i have a 2011 subaru forester. my oem maf sensor went bad. i didnt know that it could be cleaned so i bought one brand new. but now the engine light came back on and is telling me that the new sensor is faulty. what could be causing this?
Clarification: Please list the exact trouble code(s).
Don't confuse a MAF sensor code with a faulty MAF sensor. Sometimes it is, sometimes it isn't.
It could be a bad connector or faulty wiring. The code can be even be thrown from an intake manifold gasket leak.
There's a few things you can do to rule out some of these things without getting your hands dirty.
First, get your clean hands on an inexpensive scanner.
Plug it in, switch to Live Data and observe what the MAF sensor is reporting at idle.
I don't know if your Forester has a 2.0 Liter or a 2.5 Liter engine but a "loose" rule of thumb is 1g/s per liter of engine displacement At Idle.
So a 2.0 engine should be around 2g/s at idle. A 2.5 engine should be around 2.5g/s at idle.
If it's close to this then you can rule out a wiring issue or a faulty wiring connector to the MAF sensor,
Although not conclusive, I would be "leaning away" from it being the new sensor either.
Second, switch the scanner to Freeze Frame and look at what the ECT (Engine Coolant Temperature) was when the code was thrown. Look at what the engine RPMs were. Look at what the MAF sensor was reporting.
Did it happen before the engine reached operating temperature? And/or was the engine RPMs near idle? Make a note of the ECT and RPMs and then clear the code.
When the light comes on again, repeat. (Make a note of the ECT & RPMs again and clear the code).
Do it a third time. If you see a pattern of the code being thrown before warm up or low RPMs you may want to start considering an intake manifold gasket leak as being the culprit.
Third, (should be included in "Second" because you'll still be looking at that Freeze Frame data from when the code was triggered) look at what the Fuel Trim was doing. Was it adding more fuel (positive fuel trim) when the code is triggered?
Your Boxer engine has cylinders on each side of the engine. Unfortunately it only has one upstream O2 sensor (A/F sensor) so the Fuel Trim won't be able to point you to which side on the engine may have a vacuum leak.
If the MAF reading at idle seems OK, and the code is always be thrown during warm up or at idle/low rpm, with an elevated positive fuel trim, it could be pointing you toward a vacuum leak.
Did you buy another OEM?
