mzeitlin

My check engine light came on and I have a P0171 code : Bank1 Sensor lean

The engine is running great - no obvious signs of any issues - so I think it is the Oxygen sensor going out.

Which one is it???? I replaced the front one last year at 50,000 miles (closest to the radiator). I now have 58,000 miles and wonder if it is the same sensor (I installed a universal one).

The MAF is nice and clean and shiny, so I don't think that's the culprit.

appreciate any help?

truongsta8

I had this problem about 2-3 weeks ago and i thought it was the oxygen sensors that were bad so i brought to a mechanic to replace all three because it kept having the CEL on everytime we replace the 1st ones. In the end all three were replaced with BOSCH o2 sensors and the CEL was still on.........Took to lexus dealer and they diagnosis the problem to be the MAF sensor was bad. Replaced that for 460 dollars including parts and labor... Car still ran *****ty so Lexus tech says its the aftermarket o2 sensors that i replaced that NEVER needed to be replaced in the first place. So i decided to replace the o2 sensors and it ended up be 648 with parts and labor.....

MAF sensor and labor = 460
O2 sensors and labor = 648
Car running good as new with the annoying CEL off = Over a $1000

as u can see that little annoying light can cost u $$$$$

hope this helps....

mzeitlin

I thought about the MAF - so I cleaned it today with Carb cleaner and the metal wires are nice and shiny now. No change on the CEL. The last time I had the CEL come on, I replaced the front O2 sensor and the light went out for months....now it's on again, but it seems to be the other bank (by the firewall). I'm thinking O2 sensor.

Tammy

Denso made the original O2 sensor. Not the Bosch.

mzeitlin

That's good to know ... thanks...

mzeitlin

Well...I gave up. I tried to change out the O2 sensor myself and there is no way on God's earth is it possible to get to the rear sensor (Bank1) on the engine without having the hands of a 3 year old.

And the little leverage I did have, the part is certainly 'welded' in there.

So off to Lexus to spend $500 for them to do what would have cost me $65 to do. Very frustrating.

And the car only has 55,000 miles on it and it does this....NOt what I bought a brand new Lexus for....

mzeitlin

Well....guess what .... it wasn't my Oxygen sensor after all.

At the dealer, they tested further and told me it was my air flow sensor (the simple thing by the air filter). I doubted them - saying that if it were the air flow sensor, why did I get only one bank error? I should have had both banks faulty. They said, that's the way the system works. They're good guys, so I trusted them. They replaced the sensor (trivial) because I already had their time invested and sure enough, the trouble codes went away - and lo and behold, I had power and performance I didn't know the ES300 had ??@#*(@

Apparently the car ran fine at idle and steady acceleration - which is my normal method of driving this car. When you stomp on it, it goes o.k, but nothing like it does now. Now it's a jack rabbit. They told me it had probably been like this for a while, and its only now that the computer gave up and threw out the code.

I cleaned the sensor myself, but apparently it was far enough gone this time.

Car runs like it was new.- amazing.

Learn something every day.

Thanks for the posts !!!