During this diagnosis of an EGR trouble code on this Impala, I have the opportunity to go into detail about computer controlled solenoids, duty cycle, and how they relate to valve position. I also get to showcase the power of the Verus, with side-by-side scope and scan tool testing. Despite the inadvertent fix, this video makes for great study material, especially relating to sections 3, 7 and 20 in my book.

Engine Performance Diagnostics chapter 3

symptoms 50

  • check engine light (P1404)

fix 50

  • resetting the EGR valve closed position voltage (by disconnecting the battery)

test shown enh 50

  • using a bi-directional test to command an EGR valve to open/close
  • how to use scan data to evaluate an EGR valve position error
  • using a wiring diagram to understand circuit design
  • how to view the scope and scan tool simultaneously on the Snap-On Verus
  • understanding duty cycle control and frequency, relating to power/ground switching
  • how to distinguish between a duty cycle command and valve position
  • how to clean the valve seat on a GM linear EGR valve
  • checking an EGR valve position sensor and wiring with a scope
  • how to reset the EGR closed position voltage in the PCM
  • how to identify an incorrectly installed (reversed) EGR valve with scan data

Tools used

  • scan tool
  • lab scope

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(Chapter 3) Transistors, Solenoids, Computer Controlled Output Testing

Related videos:

How to test for EGR flow problems (GM electronic EGR test) - P0401:


How to test an electronic EGR valve (GM P1406 case study):


2000 Ford Focus EGR System Tests (EGR, DPFE, EVR) - P1409:


Ford EGR Flow Testing (P0401, P0402, P0405):


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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!