Question about 2000 Lexus ES 300
P0171 sets when air/fuel ratio feedback is stable after engine warm up, & fuel trim is considerably in error on the lean side.
The signal from a/f ratio sensor is approximately proportional to existing air-fuel ratio.
CHECK: system for intake leaks, incorrect fuel pressure, plugged fuel injectors, 02 sensors or coolant sensor operation.
check air fuel ratio sensors. to test main AFR sensors directly you will need a good scan-tool to test parameters.
A thorough preliminary check is important. If you take your time you may find the answer before you start playing the "process of elimination " game.
Good luck, let me know how it is going.
Posted on Apr 27, 2010
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Posted on Jan 02, 2017
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