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P0171 Keeps Coming Back Even After Replacing Oxygen Sensor...


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I have a 99 ES300 with 130K and I was getting p0171 error code and had my upstream oxygen sensor replaced with a high quality Bosch part. Now its coming again after drive for only a few miles. Its coming up twice.

Any ideas what might the culprit be and any solutions?


P.S. I'm not noticing any changes in the performance in the car.

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The following list applies to the trouble code you have. When more than one cause is listed you are ill advised to just jump to the conclusion that swapping out a single part can cure the issue. You may well have changed out a part you didn't need to. Obviously one of the other causes listed is the one that needs to be addressed. If you're not capable of tracking down and correcting any that are listed, you need to save money by taking the car to a qualified mechanic who can. Good Luck!
Possible causes for a Lexus P0171 code:

- Intake air leaks

- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

Read more: http://engine-codes.com/p0171_lexus.html#ixzz3Hf4CoOEX

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  • 1 year later...

I spent hundreds, maybe thousands of dollars over the life of my 2000 RX300 trying to resolve the P0171 error.  I've had O2 and Mass Air Flow Sensors replaced numerous times to no avail. The car always ran fine except for straining, pinging and loss of power when climbing.  I had been using regular gas for 16 years and decided to try a higher octane - 91.  Voila!  No more trouble climbing, no pinging, and best of all the error code is gone!

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