LEXUS RX300

Check out this web site or google search P0171 for possible causes.

Check your MAF sensor.

Thanks Ray butI did change the MAF,do you recommend any other solution that may solve this problem.

Why did you change the MAF sensor? Was it tested and did it test bad or did you change it in hopes of solving the check engine light? I would imagine that a bad MAF sensor would cause both Bank 1 and Bank 2 to be lean, not just 1 bank, but it never hurts to check.

After the MAF sensor was changed, were the trouble codes cleared?

A lot of people misinterpret the term "check" or "inspect" to mean "replace." For example, when I say "check the MAF sensor" I mean check the condition and operation of the MAF sensor, measuring voltage or resistance, and comparing it with the specified voltage or resistance and the wiring circuit to whatever is being checked.. Rather than checking the MAF sensor, a lot of people will just replace it. The biggest drawback to this approach is that it may not solve the problem.

Assuming that the replacement MAF sensor was new and the wiring circuit between the MAF sensor and ECU are good, then you have to check for other things that can make the ECU think that the engine is running lean.

Check the voltage and frequency of the signal going into the ECU from Bank

Look for cracks, holes, gaps, etc. in the plastic intake tube between the MAF and the throttle body (this is not a likely cause, but check any way)

Check manifold vacuum for leaks (this is also not a likely cause, but check any way).

Just by way of curiosity, are you getting enough gas or the right mixture of gas and air to the bank 1? Is the truck running OK or is it rough? What does the dealer say?

Sounds like the o2 sensor is not changing on bank one. that will leave you in a rich or lean condition all the time. change the upstream o2 sensor on bank one, should take care of it unless it is an electrical prob.

I have change the fuel/air ratio sensor on sept 9/06 The engine light came on once on sept 9/06 I have reset the computer on sept 9/06 since then the engine light has not come back on Ihope this was the problem,Thanks for everyone input.