Prius Gen 2 MAF Sensor Cleaning (Code P0171)

The MAF (mass air flow) sensor measures the mass of the air flowing through the throttle valve. Air mass changes due to altitude, temperature, etc. The car computer uses this information to determine the fuel injection time and provide a proper air–fuel ratio. (Via)

The Prius gen 2 MAF assembly has external and internal sensors.

First, the external intake air temperature (IAT) sensor:

Before: intake air temperature sensor bulb (left) obscured by deposits

After: intake air temperature sensor bulb sparkles

Second, the internal sensors: 1) Ambient temperature sensor; and 2) hot wire, kept at a fixed temperature above the measured ambient temperature:

A mini hamburger bun (?)

Wait. That debris should not be there. Wow. The other sensor seems dirty. Not sure anyone has ever cleaned these in 260K+ miles.

The car has run rough for some time--I'm guessing this explains why.

After: clean hot wire and ambient temperature wire, with debris removed

I used a Craftsman 9-4116 Offset Screwdriver Ratchet Set to extract the two screws. Others have used a flexible socket extension, etc. A bit of torque was required to loosen them.

Set it on generous layers of paper towels. Sprayed short bursts of CRC MAF sensor cleaner onto the bulb and inside the housing--as the instructions state, do not touch the components while cleaning.

I think the result speaks for itself. Cleared the code and will see if it fixes code P0171.

This project really represents something anyone can do in a very short amount of time.

The car now throttles very smoothly.

NOTES

Via:
It would dry really quick, just a minute or two. But just to be sure I let mine sit for about 15 mins then installed it. A simple trick is to spray the side of the mesh first and then the open side. If you do it the opposite order( spraying the mesh side last) all the crap from the mesh is gonna stay on the sensor. Also keep the sprayer 5-6 inches away from the sensor. So:

1. Remove sensor
2. Spray the mesh side
3. Spray the open side
4. Let it sit for 10-15. Do NOT touch the actual string with anything
5. Put it back in the car

Via:
If you are replacing the MAF, consider a new O-ring (90099-14141). If needed, new screws (90167-A0016). From any Toyota source for about $5.
https://www.toyotapartsdeal.com/oem/toyota~screw-pan-tapping~90167-a0016.html