Check engine light - P0171 system too lean -- buy new MAF sensor?

Discussion in 'Gen 3 Prius Technical Discussion' started by Doug Hansen, Jul 13, 2026 at 4:22 PM.

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  1. Doug Hansen

    Doug Hansen Junior Member

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    Plug-in Base
    I've cleaned the MAF sensor with the special sensor cleaning spray, and it worked for about 4 days but now the check engine light is back on and the same error code is P0171. Gemini says I should try clean the sensor contacts again, so I will, but if I need to buy a replacement MAF sensor, so I spend the $150 on a Denso or the knock - off that gets a 4.4 rating on Amazon and costs $25? Very few people have bought the OEM Denso, not sure why.
     
    #1 Doug Hansen, Jul 13, 2026 at 4:22 PM
  2. Brian1954

    Brian1954 Senior Member

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    What year is your Prius, and how many miles are on it?

    In most cases, the problem is not the MAF sensor. It is an air leakage problem. Check all the vacuum hoses for cracks or splits on the end of the hoses where they connect.
     
    #2 Brian1954, Jul 13, 2026 at 5:14 PM
  3. Doug Hansen

    Doug Hansen Junior Member

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    Hi Brian, it's a 2011 Prius with 101,000 miles. Hoses look fine. Clamps fine. Car has been regularly maintained. I followed Gemini and used the official spray cleaner on the MAF wires (twice) and at first the Check Engine light stops, but after a couple of miles it comes back on. So my AI "friend" says the next step is to replace the MAF sensor. Then go to mechanic and have them work on the EGR. I'm no mechanic! Ideas?
     
    #3 Doug Hansen, Jul 13, 2026 at 5:40 PM
  4. Brian1954

    Brian1954 Senior Member

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    Can you please provide a list of all the vacuum hoses that you checked?

    I do not think that replacing the MAF sensor will fix the problem.

    Have you used a scanner to look at the short and long-term fuel trims when the engine is idling and also when driving the car?

    Have you used a scanner to look at the MAF sensor data when the engine is off and when the engine is idling?
     
    #4 Brian1954, Jul 14, 2026 at 4:26 PM
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