2014 PiP - 213K KM - P0607 & P0138 intermittent

Hi all,

I have had an intermittent trouble code on my PiP since March 2022 (~195K KM), it first began when I was driving in a rural (unpaved) road on a soggy spring day with lots of puddles, though I didn’t drive through anything excessive.

My ScanGauge reported P0607 and P0138; though the P0138 often goes away quickly, replaced with P0000 (which I assume is that it cleared itself). The P0607 also often clears itself after a few days of being dry weather, and sometimes I can clear it with the ScanGauge and it does not come back for a while, but inevitably does with P0607 and P0000 (I haven’t seen P0138 in quite a while now, but P0607 is consistent…).

The car drives completely normal, and no noticeable change to fuel economy. I told the Toyota dealer about it when it first happened when I had it in for an oil change, and they did a visual inspections and basically told me not to worry about it (LOL, since they knew I was planning to change the car ‘soon’ anyway, they are cool and don’t force unnecessary stuff).

The trouble codes went away all last summer without doing anything; once the cold/wet weather came back, the codes returned and it has been on most of the winter. It is almost 100% surely related to wet conditions. It has been on and off again this spring, currently on as we are currently in a soggy week.

Most relevant systems are stock - original 12V battery (dealer tested and said was fine), catalytic converter (never attempted to be stolen, to my knowledge), exhaust system. Had the spark plugs replaced last summer and “fuel system service” including throttle body cleaning. No exhaust smoke or excessive exhaust smell, the engine does not burn even a drop of oil and seems very smooth and healthy. My EV% is only 13% lifetime, so there is estimated 185K KM on the ICE today (out of 213K overall), which is mostly “easy mileage” as I generally warm the ICE up while coasting when I know I will need it, and not push a cold engine. The car really is in great shape.

I am hoping to sell the car privately ($$) later this year when my new Prime is finally in, and I would really like to solve this annoying issue if I can to not impact my sell price, without breaking the bank (probably take it to an independent repair shop I know). However, I thought I would check with the wizards here on what the opinions on what may be causing this, to hopefully point them in the right direction, since they are a general repair shop and not Prius/hybrid specific.

I sounds like a faulty O2 sensor from what my Google research tells me, however does it make sense this code would be triggered by moisture? What type of cost should I expect to replace an O2 sensor at a non-dealer repair shop? (I.e. what approx part cost + how much labor effort to replace?)

Thanks for any input that can be provided.