Help solve my issue- if you can

Back story- 2008 Toyota Tundra 5.7L several months ago I had a secondary pump/valve issue- code P2440- truck lights all on / limp mode.
($3,700 at the dealership wasn’t what I wanted)- I ran a gen 1 Hewitt bypass kit and everything was fine for a few months.
Current issue- driving on freeway and all the lights come on (just like before- 4Lo, engine, stability, etc). I pulled over, disconnected battery and everything was fine (BTW- engine did Not go into limp mode this time). I contacted Hewitt and they told me to run codes- so I did. This time P0174 and P2197 (both too lean bank 2 sensor 1)
This didn’t seem right since the Cat and sensor were fairly new on that side. I replaced the Mass Air Flow sensor and PCV valve- my next step is to replace O2 sensor but …
When an O2 sensor is bad only the check engine light comes on (and all the time)
My warning lights seem to only get triggered when I drive above 65 mph? any ideas???

 

One note- my truck runs perfectly fine on surface streets- this only happens on freeway at 65 mph or above- I reset codes by disconnecting battery to continue driving.

 

First guess is that you have a small exhaust leak where the cat pipe joins with the exhaust header. This will suck in air during the negative presure phase of exhaust pulse and this inreases the O2 level seen by sensor (more O2 is lean). Tech may have been sloppy assemblimg that joint. Another possibility is that the new upstream O2 sensor is failing. Not common, but happens. You will NOT always get a code for a bad sensor; Only certain type of sensor failures throw codes.

Needs more diagnostics. Need to drive around while observing ST fuel trims and AFR to see what conditions are going lean or strange sensor behavior..

 

Thanks- wouldn’t a leak cause issues at any speed?
I’ve renamed my issue the “back to the future” issue.. but instead of 88 mph… my fail happens above 65mph.
Can I do the ST fuel trims and AFR tests myself or is this a “take it to a professional” thing?

 

Usually it is rpm or air flow that will factor into where the system is lean enough to trip codes. You can buy a cheap obdii code reader from Amazon for $20. Connect it and go to live data, then scrol to stft-short term fuel trim. Then drive around and observe. Your computer has a big table that tells it how much fuel to use for any given rpm air flow combo. If the o2 sensor doesn’t read where the computer wants it, it adds or subtracts fuel untill it does . If the stft is positive, the computer is adding fuel beyond the table. 10 means 10% additional. -10 means 10% reduction. In a perfect world, the table is pretty accurate and the stft’s are les than 5.

let us know what you find and maybe we can help narrow it down. I cannot tell you why it is consistently tripping at 65 other than that is a symptom, not a cause. Possibly related to the logic in the ecu.

why it is lean is not an easy question to answer. Much detective work involved. Vacuum leaks and bad o2 sensors are high on the list though.

 

I bought a code reader- great investment. Turns out it was my bank 2 O2 sensor. Replaced it with OEM sensor and so far- problem fixed .. thanks for the advice