I installed a new battery and the engine is now throwing - P0171 -> P0101 -> P0138. Prior to the battery install I had never had a CEL come on since I've owned it. It's a 2008 with 180k miles on it.

I don't notice much other than little shake/knock at low RPM after starting up. Once it's warmed up, it seems to go away.

This is based off the scan from AutoZone

P0171 -System too Lean (A/F Lean, Bank 1)

Secondary DTCs

P0101 - Mass or Volume Air Flow Circuit Range/Performance
P0138 - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2


I replaced my MAF with a Denso (bought of Amazon and assume it's real). Any advice on what my next steps should be? Based off what I've read it could be a whole slew of things - O2 sensor, fuel injectors, manifold leak, or other vacuum leaks.

I would be suspect of any "genuine" Toyota part from Amazon or Ebay. If you kept your old MAF and it still works, put it back.

I was sitting in a bank drive-thru with my '04 a number of years ago when about 3-4 lights suddenly lit up on the dash. I took it to the dealer and they said it was the O2 sensor. They said the sensor can cause other lights to come on. They replaced and reset the codes. It's been many years and I've not had any more lights come on, except low tire and when I trip the DAC by accident.

Since one of your codes is the O2 I would suspect that.

tried resetting the MIL, disconnect the battery for 15mins...then reconnect, start the car and relearn/idle for 7minutes