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
https://www.youtube.com/playlist?list=PLAFYVCyenqcr32wgsCqa1Zj4335YlBF5p

Related videos
- Multimeter basics, voltage and resistance tests (a ScannerDanner Premium video)
https://youtu.be/w0PpLTnKKZg
- Low Fuel Pressure from a bad fuel pump ground (Ford Ranger)
https://youtu.be/rQ7tvIxQSt0
- MAF sensor trouble code (P0102) caused by a bad ground (GM 3100)
https://youtu.be/bJRLZnjS6ms
- How to test a starter motor (no crank from a bad block ground) - Nissan
https://youtu.be/ytrcqM8wyW0
- Bad Engine Computer Testing Part 1
https://youtu.be/hJQ6qnhTgdg

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.
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 https://www.scannerdanner.com/join-scannerdanner-premium.html There is a 14 day free trial.
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