How to test a computer transistor driver with a basic test light. This test is especially valuable when you have a faulty solenoid and cannot rely on voltage changes with the circuit activated and deactivated. Also this is the fastest way to verify wiring integrity of the control wire. A manufacturer flowchart will have you disconnect the computer and solenoid, then measure for opens and shorts with an ohmmeter. It's absolutely ridiculous that this is the standard method of testing a circuit!

Before performing this test, you must know what polarity to connect the test light to.

Watch this video to determine circuit design:

How to test a computer controlled solenoid (power/ground side identification)

Engine Performance Diagnostics chapter 3 page 12

test shown enh 50

  • how to test a computer driver
  • how to test the control wire for opens and shorts
  • how to force an output driver to turn on without a scan tool
  • how to force an EGR solenoid circuit to turn on

Tools used

  • LED test light (preferred for computer driver testing)

end faq

{accordionfaq faqid=accordion15 faqclass="dotluvfaq help2 aligncenter headerbackground headerborder contentbackground contentborder round7" active=item0}


(Chapter 3) Transistors, Solenoids, Computer Controlled Output Testing

Related videos:

How to test a computer controlled solenoid (circuit ID with voltmeter):


How to test a computer transistor driver (using a scan tool):


 How to test a computer controlled solenoid (power/ground side identification) :


end faq

{accordionfaq faqid=accordion3 faqclass="darkhivefaq defaulticon headerbackground headerborder contentbackground contentborder round5" active=item0}

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!