Weird Codes

So I have a 2010 Toyota Prius. It has about 238k miles. In the last year I have gotten a new water pump, belt and EGR line.


It has had a consistent problem with burning oil very fast- as I’m aware hybrids will do, due to their start stop function and carbon build-up.

It also would have clouds of blue tinted exhaust coming out while idle.


I’ve over time just been diligent on filling up the oil etc.


Recently I got a few error codes. P301, P138 and P401. What I did to try and resolve this was replacing the spark plugs, I noticed there was oil in the spark plug well, like a lot. I think this is due to me not using a funnel and accidentally spilling a bunch of oil. Anyways, I dried out the wells with shop towels and a screwdriver, I left them in there to dry for a while and then replaced the spark plugs.


The next thing I did was remove and clean the intake manifold. There was a ton of carbon in there, it looked like coffee grounds. Cleaned it with Sea Foam Intake Spray. I also replaced the PCV valve while I was down there. There was carbon crap on that too.


I removed the EGR line and part of the EGR cooler to place a new gasket on it and clean it out. There was so much carbon in it it was nearly completely blocked off.


Afterwards I put everything back together. Then I jacked up my car and replaced the down-stream O2 sensor in attempts to appease the P138 code. The previous sensor was a pain to get off and was black all over the part that goes into the catalytic converter.


After this, no more rough idle and my MPG went from an average 27mpg to 32mpg. At a quarter tank I threw in some cataclean. I went to get the CEL reset at autozone and it came right back on. All the same codes were there, along with a new one- PO328. I thought maybe this is just because they are “permanent” codes and need a dealer to reset them. But I have a new code now, and my mpg dropped to 25 mpg. My exhaust seems to be MUCH better.


Not sure what is going on or how/if these codes are connected in some way, something I may be missing. Fluids are good, air filter is white. I’m pretty much at my wits end for diagnostics. Hoping someone maybe could shed some insight. Thank you.