This is a three part series (10 minutes each) on a Jeep that has a no start, no spark, no injector pulse, no communication problem.

We brought this case study into the classroom during a period when I was teaching my students about "The 5v reference circuit" (Chapter 9 in my book).

Our approach in troubleshooting this problem is focused on the missing 5v reference. As you will find out in the end, it is simply a blown fuse for the ECM, however the procedures I show on how to test this 5v reference circuit can be applied to every single car out there. Be sure to watch the "Related videos" posted in this description for other case studies that actually have a shorted 5v reference circuit.

Engine Performance Diagnostics chapter 9

symptoms 50

  • no start
  • cranks normally
  • no spark
  • no injector pulse
  • fuel pump runs continuously with key on
  • no check engine light

fix 50

  • replace blown ECM fuse and repaired shorted oxygen sensor wiring

test shown enh 50

  • how to test computer powers and grounds
  • how to check the 5v reference circuit
  • how to determine if the engine computer is "alive" or "dead" by using the 5v reference circuit as a guide
  • how to test a circuit for a short to ground
  • how to test for a shorted sensor
  • how to locate and repair a short to ground in the wiring harness of a car

Tools used

  • scan tool
  • digital multimeter
  • incandescent test light
  • wire cutters
  • soldering gun
  • solder
  • heat shrink
  • short circuit tester

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(Chapters 9, 10 and 11) The 5v Reference and Signal Circuit Quick Tests

Related videos:

Part I of this series :


Part II of this series :


No Start from a shorted MAP sensor (Honda, Acura):


How to check the 5v reference circuit for a short to ground (Cadillac):


Bad Engine Computer Testing Part 1 :


Bad Engine Computer Testing Part 2 :


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


end faq

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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!