My wife had my truck today and called to tell me she had a check engine light. I told her to run over to Autozone and have them pull the codes. They pulled a P0138...O2 sensor.
This is the second time it has lit. She had the light last time she took my truck about 2 or 3 weeks ago. I disco'd the battery to clear it just to see if it would come back or not.
My first question is why is this only lighting when she has the truck??? I have been driving it for the last 2-3 weeks and it's been fine. She takes it and BINGO...there goes the CEL. Is it her driving style or just a coincedence?
Second question is which O2 sensor is the P0138 pointing at?
Thanks in advance...

 

try taking the sensor out and cleaning it with a electronic cleaner. my truck was having the same problem, i had to replace my plenum gasket, leaked tons of oil into the intake manifold and in turn clogged up the o2 sensors. try cleaning them before spending the $70 bucks on a new one.