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According to a 2002 Toyota RAV4 Repair Manual, "If total of short-term fuel trim value and long-term fuel trim value is within plus or minus 38 percent, the system is functioning normally."

Based on fuel trim posts that I've read or watched, this range seems a bit excessive.

Can anyone "validate" these ranges as being "normal" for assuming no known mechanical issues and codes in the vehicle?

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    generally +/- 10% ltft is acceptable anything more would probably set a code. +/- 38% total fuel trim still seems excessive and would likely cause a code as well.On Toyota's when AFR sensor goes bad or a vacuum leak occurs you'd see ~ +25 ltft. – Ben Sep 1 '17 at 20:33
  • @Ben - Yes, +/- 10% seems to be the "normal" good range. However, I can confirm that codes are NOT being set for total FT > 10% or even up to +28%. This assumes scanner, PCM, and AFS (up-stream sensors) are operating normally. – InfinitelyManic Sep 1 '17 at 20:40
  • I don't have a capture from a 2.0 Rav4 but I do have a capture from a 02 1.8 Corolla with a p0171 code and total fuel trim of + 21% at idle ltft +23% STFT -2% FWIW. If you see low LTFT at idle and cruise you can assume the system is working normally for the most part. – Ben Sep 1 '17 at 20:57
  • @Ben - copy/paste from 2002 Engine Performance, Self Diagnostics, Test With Codes section; "When DTC P0171 exists, the actual air/fuel ratio is to lean. When DTC P0172 exists, the actual air/fuel ratio is to rich. If total of short-term fuel trim value and long-term fuel trim value is within plus or minus 38 percent, the system is functioning normally." – InfinitelyManic Sep 1 '17 at 21:30

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