I have a 2009 Prius and get the p2196 almost every time I drive the car. The rich condition only happens occasionally during off throttle deceleration, typically after a period of having been heavier on the throttle, and it only happens briefly. I have watched the real time air/fuel and seen it spike for a brief second to trigger the code. After the code appears I can clear it right away, and it stays away until it gets similarly triggered again. Thanks for any help.
I got a Prius with this problem but the other error code related to this... P0138. I've read threads about replacing upstream sensor solving the problem but I don't know the tune up history of this 2004 Prius. So I plan to do the tune up/engine care first and then work on the error code next. Of course I haven't seen the error code in a while, so I might lose my motivation...
What region in the US are you? As in what's temperature and humidity / weather where you're having those symptoms? I got a Prius in PNW with this problem but its the other error code related to this: P0138. I've read threads about replacing upstream sensor solving the problem but I don't know the tune up history of this 2004 Prius. So I plan to do the tune up/engine care first and then work on the error code next. Of course I haven't seen the error code in a while, so I might lose my motivation... How about you? What's your engine care history?
I can verify that both upstream and downstream sensors have been replaced with OEM new ones. It also has a new MAF sensor. It is also worth mentioning that I drive the car hundreds of miles a day on average. It used to burn a ton of oil, but a b-12 piston soak got it down to burning slightly less than a half a quart between oil changes.
If you want to find out if your ECU is correct - pull your spark plugs and inspect the tips. If you don't know what a lean vs rich burn spark plug looks like - there's plenty of examples on an internet search. What are the chances that you have a leaky injector or two. Spark plug should tell you that too. Hopefully you've got a clean air filter and checked your air intake pathways are clear. Good Luck....
Any chance that through all those efforts the 12v battery was never disconnected and reset? Aside from that, sounds like it's time to start getting way more detailed data via Toyota Techstream or Autel... Also, as always when diagnosis gets hard, check for bad vacuum hoses and wires and plugs that could be better.
