In this video I will show you how to test a crank sensor on a GM 3.8L (3800) engine. This same type of crank sensor is also used on the 3.3L (3300) engine. It is a hall effect type and it produces two separate signals. One is known as an 18x signal (18 pulses per 360 degrees of crankshaft) and the other is known as a 3x signal (3 pulses/360 of the crank). The 18x is used for timing and misfire monitoring and the 3x is used to synchronize the 18x signal. If you lose the 3x signal while the car is running, it will continue to run until you shut the engine off, then it will not restart (no spark). If you lose the 18x signal, the engine will shut down immediately and it will not restart (no spark). There was nothing wrong with the sensor in this video, I am just showing how to test this design.

Engine Performance Diagnostics chapter 21

test shown enh 50

  • how to test a hall effect crank sensor with a scope
  • how to perform a bypass test with a test light
  • how to test an ignition module on a GM 3800 engine
  • how to test the crank sensor using scan data

Tools used

  • lab scope
  • scan tool
  • incandescent test light
  • backprobing pins

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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):


Hall effect cam/crank sensor operation and testing Part 2 (an SD Premium video):


How to test a GM 3-wire crank sensor (hall effect type):


Camshaft Position Sensor Circuit Quick Test:

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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.

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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!