This car had multiple problems. In this particular video I will be showing you the cause of fixed lean oxygen sensor signals (both banks) and very positive STFT and LTFT numbers. I will also show you how to use fuel trim after the repair to determine if you have any other problems.

Engine Performance Diagnostics chapter 1


  • high idle speed
  • check engine light (P0171, P0174, P1506)

fix 50

  • replace cracked and damaged PCV hose under the throttle body

test shown

  • how to determine type of lean condition using fuel trim
  • how to verify a vacuum leak using fuel trim at different loads
  • how to test for oxygen sensor function
  • how to find a vacuum leak by sound
  • how to find a vacuum leak with water

Tools used

  • scan tool
  • spray bottle with water

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(Chapter 1) Misfire ID, Compression Tests, Vacuum Leaks, Fuel Trim, Head Gasket, Restricted Exhaust, Low Power, DMM

Related videos:

System Too Lean (P0171, P0174) - Vacuum Leak Quick Test - Ford 5.4:


Causes of lean condition trouble codes P0171, P0174 - GM 5 3L:


P0507 Idle Speed Performance Higher Than Expected (vacuum leak) - Jeep


Ford F-150 P0171 P0174 Trouble Codes - vacuum leak (water test):


How to find a vacuum leak with water:


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For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available as an eBook or paper book.

Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium. There is a 14 day free trial.

On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!