QuestionMy check engine light came on and the PCM detected an incorrect gear ratio condition in the 4th gear (P0734. The truck runs fine. This code is the only indication of a problem. It also determined that the fuel system for bank 1 (P0171) and bank 2 (p00174)was too lean. They told me to replace the O2 sensors to correct these problems. Is this what I need? If not, What is the problem and how can I fix it?
AnswerI think you should clear the faults first, because very oftenly storing the ECU-s false faults, then if the problem comes forward again in a short period, you should check the sensors signal. Is it NAS (North American with 4 o2 sensors)model? If just two, in hot conitions the outputs must switching between 0 and 5 volts, oftenly (if not changing, try to kick the throttle pedal once).
The P code exact definition: "Additive injector adaptive fuelling - lean limit exceeded", so in my oppinion if it's true there may be some plus air can get into the plenum chamber. Check all the vacuum, and air tubes for airtight.
I think you should clear the adaptive values from the automatic transmission, and the engine ECU.
