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RX300 Bank1 too lean, bad smell; P0171

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Hey Folks,

My wife drives a 99 RX300 with 225K. I have a code for bank 1 too lean.


  • knock 
  • horrible smell from the exhaust
  • studering with acceleration at 60 mph
  • rough ideling

I found two air leaks and it ran better but the code returned and after a tank of gas, the smell also returned with a sharp decline in fuel econemy.

Today I cleared the computer and I have a returned code but the smell is not present yet. 

The good;

  • no air leaks
  • maf sensor working
  • catalytic converters seem to be good (lean code and smell is not consistant)
  • Fuel Filter, plugs done in the past 6 months
  • injectors cleaned 6 months ago

Does anyone have any ideas? Does anyone know which oxygen sensor is bank 1? I am going to replace that and see if we have improvement) 

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Hi. How did you clear the computer? My 2002 RX300 had almost all of the symptoms of your wife's vehicle. I followed the advice of an RX300 owner and a Mercedes owner; disconnect battery for a full 24 hours; reconnect the battery, retune the radio and drive as fast as you are allowed (maybe 5mph over) for 25+ miles then turn around and do it again (return) until you attain at least 50 miles. My vehicle ran almost like new and the sensor lights haven't come back on...almost a year ago. FYI, Pepboys showed that I had a vacuum leak also. I also waited until an early Sunday morning to drive my 50+ miles, on a highway (you don'twant to do this in your neighborhoo), so I could go fast without interruptions. If you do this keep an eye on your AVG MPG Readout, if you have one; you'll be amazed at what you see. Anyway, this is what worked for me and others but, your wife will be without her vehicle for at least 24 hours.

Good Luck Sir.

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Hey John,

That is so strange! I used Scotty Kilmer's method on Youtube for clearing the eco. I disconnected the battery, turned on the lights and interior dome light so it would drain the computer of any charge at all, let sit for 5 min. Then I idled in N for 4 min, Idled in L for 4 min then took it on average 50 mph hour for an hr round trip... Not quite 50 miles. I am going to look for what others say and I might try your method more precisely. Thanks for the input!

Best, Justin

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My pleasure Sir. BTW, I actually disconnected both battery cables when I did mine, not just the Positive as some do. I've also heard about others trying to pull a main fuse (somewhere on the firewall) to reset the computer but, I've been told that won't work for the complete reset.

I did see the video you are referring to but, when I actually found people with the same codes and supposeded vacuum leaks I went with their ideas. I just can't believe that it was a Mercedes AMG website where I first learned the method, afterwards I found the Lexus owner saying the samething. You may also want to make sure you have at least half a tank of gas; I read somewhere that the amount of gas can effect your resetting of codes and the computer as a whole; mine was full, with Premium, when I did my reset. Just so you know, the RX300 owner said he does his reset almost weekly because the cars learn our driving habits and adjust accordingly; I think weekly is overkill but, he is a 4WD off roader and maybe he needs it that often.

Again, good luck Sir.

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  • 2 weeks later...

Well, cleaning the computer and hauling !Removed!, lasted longer than I thought. I replaced the bank 1 Oxygen and a/f sensors today... Fingers crossed that cures it.



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