What do you do when the flow chart leads you to engine computer replacement? Think outside the box! This case study emphasizes why I think manufacturer flow charts are misleading, and shows what tests you can do to avoid replacing a computer for nothing.

Engine Performance Diagnostics chapter 21

symptoms 50

  • check engine light (P0335, P0520)
  • long crank time
  • starting fluid required to start, especially cold

fix 50

  • repaired camshaft position sensor wiring
  • replaced the camshaft position sensor

test shown enh 50

  • understanding GM 7X and 24X crankshaft position sensors
  • how to test a three wire pull-up hall effect sensor and wiring
  • how to perform a short to ground test with a ohm meter
  • using a wiring diagram to identify computer power and ground circuits
  • understanding internally sourced/externally separate PCM voltage feed circuits
  • how to disassemble a camshaft position sensor connector and repair bare wires

Tools used

  • scan tool
  • lab scope
  • heat shrink/electrical tape/conduit

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(Chapter 21) Ignition inputs, cam and crank sensors

Related videos:

Hall effect cam/crank sensor operation and testing Part 1 (an SD Premium video):


Bad Engine Computer Testing Part 1:


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


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


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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!