P2196 - how to tell which O2 sensor? (2010 Prius)

Both air/fuel and O2 are id'd in this Repair Manual excerpt:

 

That's a good illustration of why it's rarely useful to try to make decisions from the text "fortune cookies" shown for codes on scanners, especially generic ones, or generic code lists or internet searches.

If you turn to P2196 in the repair manual (more info), your questions get answered pretty well right on the first page:



... plus you get 24 more pages in that section telling you what can happen to set that code and what tests you can do to figure what the cause was in your car, and what to do about it.

 

Here's that:

 

Did the thread originator ever find the root cause of the code?? I have the exact same situation (replaced engine in a 2010 and got this code). Thanks for the response in advance!!

 

I see that Mendel posted the code details and troubleshooting steps from the repair manual in post #5. The best way for you to find what's causing the code in your car will be to follow those, just as it was the best way for the thread originator to find what was causing it in his car.

 

Hello hope you all doing great need your help I have been to mechanic and he hasn't been able to diagnose exactly the problem
I am getting these 2 codes
P0420 (catalyst system efficiency below threshol Bank 1)
Mec asked me to change fuel ratio sensor (one in engine compartment)
After changing that I start getting another code
P2196 (O2 sensor signal biased stuck rich bank 1 sensor 1)

Should I change the sensor at the bottom by exhaust ?

 

Just changed the engine too, and after 2 days testing the car just got this code. How did you solved it? I just cleared the code thinking the ECU needs more readings with the new engine and it's sensors to adjust.

 

Mendel attached the troubleshooting steps in post #5 here.

Between what caused the P2196 code for wsalopek, and what caused it for JCEze, and what caused it for Kashif1, and what's causing it for you, you'll benefit the most from finding out what's causing it for you. The troubleshooting steps should help you find that out.

 

Have you read it? The only step missing is to stand in one feet, jump 3 times to the right another 3 to left and then say Shazam! I have in common with jceze that we both changed engine and after that we got that DTC. I kept most sensors on replaced engine, but probably it is better to install those from the old one starting with the A/F ratio sensor. Fortunately, I am still keeping old sensors and parts in case something may be needed during the first testing days days. Hopefully jceze can confirm what worked to him. "JCEze was last seen: Dec 27, 2021" or maybe not

 

I've looked at it ... what I see is 25 pages of information about what the code is telling you, including 15½ pages of inspection steps to try to pin down what could have caused the ECM to see what it saw. The steps include things like:

• Forcing the actual mixture rich and lean to see how the sensor readings respond
• Checking the sensor reading during fuel-cut deceleration
• Checking the sensor readings at idle, at 2500 RPM, and at closed throttle
• Checking the sensor heater
• Checking for proper EGR valve operation
• Checking sensor wiring
• Checking for a dodgy ECM
• Checking for intake leaks

which seem a lot like the kinds of things that would need to be checked to pin down one of the numerous possible root causes of this code.

It's not a code I've personally had to troubleshoot before. If I ever do, I'm sure I will find this procedure tedious and the interpretation in some places to be puzzling. I might end up hoping for help from @mr_guy_mann or somebody. But I would probably have to dig in and start doing it. When there are so many ways a code can be caused, the odds aren't very good that what's causing it for me will be exactly what caused it for somebody else. (Even if the somebody else and I just did the same very invasive thing like an engine replacement—there are enough ways to leave something catawampus in such a project that it's still not that likely we have the same root cause, unless we managed to make the exact same mistake doing the work.)

 

I wanted to share my recent experience with the P2196 error code, hoping it helps someone save some money in the future!

1. Replaced the upstream O2 sensor with genuine Toyota parts—no luck (~$300).
2. Replaced the downstream O2 sensor with genuine Toyota parts—still no luck (~$300).
3. Replaced the MAF sensor—no luck (used a donor part).
4. Cleaned and tested the fuel injectors—no change.
5. Cleaned the EGR valve—still no improvement.
6. Replaced the entire catalytic converter and exhaust system with genuine Toyota parts—no luck ($2200).
7. Finally, replaced the fuel pump with genuine Toyota parts—Bingo! The error code disappeared immediately, didn't even need to drive 100 miles ($500).

Who would've thought a faulty fuel pump could trigger a completely unrelated error code P2196. The only reason I replaced the fuel pump was due to a casual suggestion from an experienced mechanic at Hybrid Pit. Big kudos to him!

Jack

 

Thanks for sharing! It is just unfortunate that ya had to pay almost current value of the car.

 

If the injectors are not getting enough pressure, or intermintant flow/pressure, the
injectors cannot produce a mist so the fuel won't burn fully so the O2 sensors
will report too rich of a mixture. Then the computer will then lean the mixture, and things
will get worst.
Mercedes had this issue on some of cars in the late 80's....

That's why it's always good to do diagnoises to find out WHY they reporting what they are.

 

Well, I just replaced the a/f ratio sensor with the one from the exploded original engine and no more dtc, just 15 minutes job with the right socket for oxygen sensors.. It is just strange the sensors looks different since the original sensor does not required special tool. The one from the new engine had a part number stamped, and when googled is indicated to be for a prius 2011 too. Maybe the computer is just used to the usual signal range from the original sensor.

 

In my case, I did what was the most logical reason for the code. But I was ready to do the the 15 pages troubleshooting procedure and the rain dance if the replacement didn't work.

 

Sometimes, you just get lucky!