The code has been on for a long while now. In the mean time I have installed a MAF sensor, checked for air leaks and fuel pressure. I changed the sparkplugs and fuel injectors from Bank 1 to Bank 2, same results. I installed 2 new O2 sensors: same P0171 code. I changed the O2 sensors from Bank 1 to Bank 2, same code.
I then disconnected the O2 sensor from Bank 2, just to try things. I expected a different read out on my scanner. Nothing changed in the data. The car did drive differently though, with fuel consumption through the roof while the O2 sensor was disconnected. Engine light was flashing. I assume that the catalytic converter gets too hot.
Does this indicate computer problems? How do you find out if computer starts to malfunction?

 

The sensors that you replaced .. are they OEM?

Salim

 

+1. Please give us some more info. Eg, how did you check your fuel pressure and what were the results? What brand/type spark plug did you use? Etc.

 

Only one was OEM and they were exchanged without any difference. Fuel pressure was done by someone else and there was no problem.

 

It's recommended to use only Denso. The ECU has a hard time recognizing data from other sensor manufactures , such as Bosch.

What was the only one which was OEM? Spark Plugs, or the two oxygen sensors?

 

Are you related to kford1040?

 

One sensor was an OEM and the other was from the dealer

 

Was the one from the dealer made by Ginsu? I've heard that Ginsu makes great knives but sometimes their sensors are not so good. Also, you should ask the person who checked your fuel pressure to remove and dye check your muffler thrust bearings. They often go bad and throw a P0171 code.

 

Thanks for the answers so far. We do want to check out if the computer is at fault. Does anyone know if a 99 and a 2000 model computer would be compatible. The junkyard has a 99 model and ours is a 2000

 

Before opting for a brain surgery on your RX, it may be worth while to get an expert opinion from Lexus. Although the engine "run" is the most important function of the cpu, but there are lots of other little little things stored in there like key-chip-id etc.

Salim

 

I don't know if you solved your problem but here is some info for doing diagnotics...

I hope you figure out your issue...

 

Muffler bearings?? really, man? I know it's fun to kid around while in the shop with your buddies... I know! I'm a Triumph and Moto Guzzi certified tech... we would laugh and laugh when someone on their suzuki thought their power band was broken - we kept large rubber bands around for just that occasion, and we'd joke about muffler bearings and all sorts of silly sh-t, but this is a place where we come to get some real answers - some of us have no other way to get around and are missing work because our car is broken down. So maybe keep the silliness for a thread where someone isn't really having problems.

If I came off harsh, sorry - it's only 8am and I haven't had coffee yet.

Bear