In this video I’ll be demonstrating some test procedures for no communication and suspected engine computer issues. Most communication issues start with checking pin 16 of the Data Link Connector for voltage, but this video goes much further. I also have the chance to show exactly why I believe strongly in voltage drop testing, and why the ohmmeter will get you in trouble. A professional scanner and scope were shown in the video, but a simple code reader and DVOM would have worked just as well.

Engine Performance Diagnostics chapter 1 pages 23 - 25

symptoms 50

  • runs rough
  • long crank/no start
  • stalling
  • no communication
  • check engine light flickering, changing brightness

fix 50

  • clean and tighten corroded computer ground at engine

test shown enh 50

  • how to check for communication with the PCM
  • how to use the behavior of the check engine light as a guide
  • determining if a no communication issue is related to another symptom
  • how to verify the integrity of your scope/DVOM ground before testing
  • identifying Data Link Connector (DLC) pins for testing
  • how to check for voltage at pin 16 of the DLC
  • how to ohm check for ground at pins 4 and 5 of the DLC
  • how to use a scope to check for activity on a communication network
  • using a wiring diagram to check for communication network issues
  • using a pin voltage/wiring diagram chart to identify PCM power, ground and communication circuits
  • how to perform PCM power and ground voltage drop tests
  • how to perform PCM ground resistance checks
  • how to decide when using an ohmmeter is required

Tools used

  • scan tool
  • lab scope

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Ground circuit problems

Related videos:

Multimeter basics, voltage and resistance tests (a ScannerDanner Premium video):


Low Fuel Pressure from a bad fuel pump ground (Ford Ranger):


MAF sensor trouble code (P0102) caused by a bad ground (GM 3100):


How to test a starter motor (no crank from a bad block ground) - Nissan:


Bad Engine Computer Testing Part 1:


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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!