Prius 2008 - P0171, P3190, P0A0F : Next steps?

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Was that the downstream oxygen sensor, and did you purchase an OEM/Toyota or Denso sensor?

At 200k, you should consider replacing the upstream A/F sensor (Toyota/Denso only), as they don't last forever.

Your Long and Short fuel trims are quite high, this could be your sensor. You might try adding some PEA to the gas tank to clean things up.

Hopefully you didn't purchase these online as well. There are plenty of counterfeit plugs (and other parts) these days, best to shop local.

FYI : you're moderated until you've posted 5 times.

 

There have been other posts that have mentioned the upstream sensor to cause issues with poor power. Did you replace that? If you did, hopefully you used the correct Denso part. I don’t think the downstream sensor would affect your power

 

Wasn't actually sure if you've been step by step through the workups for your reported codes (DTCs). Below are said workups :

Here is the workup for DTC P0171 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2054m/cip0171.pdf

Here is the workup for DTC P3190 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2054m/cip3190a.pdf

DTC P0A0F has five (5) associated INFs (aka subcodes or detailed codes), knowing an INF for a related DTC may help in diagnosing the problem while saving effort or money. Many will use techstream on a windows device (or emulate) to retrieve the INF/subcode.

Here is one of the workups for DTC P0A0F with an INF of 238 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/repair%20manual/04pruisr/05/21bpm/0a0f238.pdf

Must've missed the upstream part, but now we know.

Given the fuel trims, DTC P0171, and the installed aftermarket A/F sensor, then replacing with a quality A/F would be my first thought.

Some here have successfully used aftermarket sensors, but they rarely report back with a part # that worked for any length of time.

 

I would focus on the P0171 code- that is likely what is causing the other codes as well.

Now for a quick tutorial. The ECM uses input from several sensors (MAF, ECT, APP, RPM, etc) to determine what base fuel amount to inject for operating conditions at that moment. If the fuel pump and injectors work as they should (and engine is mechanically sound), then the actual air-fuel mixture in the cylinder should be close to what the engineers want.

But lots of things can cause the mixture to be off, so there's some form of sensor in the exhaust to measure the mixture after combustion. A narrow band oxygen or Lambda sensor can only read mixtures very close to 14.7:1, while an Air-Fuel sensor can read a broader range of mixtures (maybe 12:1 to 16:1 or more). Most cars use an A/F sensor "upstream" of the catalytic converter as primary fuel control. The "downstream" oxygen sensor after cat is mostly used to monitor cat function (it can also be used to tweak mixture under some circumstances).

Based on those sensor readings, the ECM can determine if it needs to add more fuel (a positive fuel trim) or remove fuel (a negative fuel trim). 0% would be no correction needed. Short Term Fuel Trim is a direct response to the A/F sensor. If STFT gets too far from 0, then Long Term Fuel Trim steps in to bring STFT back. LTFT values are saved in memory. ST + LT = total trim.

Now, there are a couple things that stand out on the freeze frame data that you posted. First is the very high fuel trim values (that's what triggered the code after all). Those are in response to the voltage reading from the A/F (S1) sensor. The scantool shows about 3.3V at 14.7:1, it goes lower when it's rich, and higher when lean - your capture shows 3.6V.

The interesting part is the reading from the S2 downstream oxygen sensor, 0.95V. That's filthy pig rich. Which contradicts the A/F readings. Combine that with the low mpg, recent install of no-name A/F, and other codes; your "new" sensor is lying.

I think that putting in a genuine OE or Denso sensor will fix things up. Hopefully this hasn't gone on long enough that it's plugged the cat with soot.

Posted via the PriusChat mobile app.

 

Mm, yeah, good catch, seems likely to me.

Sometimes filthy pig rich just turns the catalytic converter into a nice afterburner for all that extra fuel, and melts its honeycomb into a big lump.

Gotta love an OBD-II app that shows throttle positions to fifteen significant figures. I wonder how long before the accessories market has a "super-high-precision throttle body" for sale to make use of such precise positioning!

 

I am happy to see this post, unhappy for your misfortune but happy to find something just like my last winter... Although I have the added bonus that I got LPG (GPL) installed also... the funny part: the car runs smooth on LPG, and grumpy on gasoline.
From seeing those numbers in the freeze frame, I see lots of similarities to mine especially in the winter during cold starts.
added bonus: I don't understand much about engines, I don't speak much Polish, my mechanic is a gearbox specialist not much into engines too and doesn't speak english, Dealership doesn't really appreciate the LPG installation and also not much english speakers too (except the sales people)

@BDenis don't be demoralized, did it finally got fixed and giving you joys? I got my prius 2005 since 2018 (already jumped the ODO barrier 299999km to 0) and I am pretty you're gone be very happy with yours

Regarding this app Car Scanner, I also use it and this dashboard version looks really interesting although it gave a bit work to organize:


I have all the summer to find out someone (Polish workshop) that is brave enough to check it because during winter it gets really ugly, just during warm up xD

btw... thank you guys for the great community