Poor running, flashing CEL, no codes (bad computer ground) - Toyota

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

Fix
clean and tighten corroded computer ground at engine

Tests shown
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

Playlist
ground circuit problems
   • ground circuit problems  

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