AUSV 2520 – On-Off and Pulse-Width Modulated Solenoids

From WeberAuto.

This video is intended for students in the online AUSV 2520 Automatic Transmissions class at Weber State University in Ogden, Utah. This class is normally taught face-to-face, but due to the COVID-19 Pandemic, I am attempting to offer the class material online. Suggested quiz questions are shown below the video timeline. You should have watched the following Clutches, Bands, and One Way Devices video first

The tool used in the video is part number J-44246, it is available from GM Tools at

The audio quality is not as good as I would have desired, but the school is on lockdown because of COVID-19 now and I cannot reshoot this video.

0:00 Introduction
0:10 On-Off Solenoid Introduction
0:23 The three different ways a solenoid must function
1:16 Electrical operation
1:55 Special service tool demonstration of mechanical and hydraulic operation
4:10 The two main computer inputs for solenoid control
4:54 A properly functioning solenoid
5:40 A solenoid with a hydraulic failure
6:30 A solenoid with an electrical failure
7:54 Pulse-Width Modulated (PWM) solenoid variable fluid pressure
8:29 Duty-cycle of PWM solenoid
9:00 Shift quality control

All Solenoids must work three different ways:
1. Electrically – Electrical current is run through a copper coil of wire creating a strong electromagnetic field. This magnetic field pushes or pulls on a spring-loaded plunger inside the solenoid
2. Mechanically – A spring-loaded plunger inside the solenoid is used to seat a metering ball or valve to block the flow of fluid.
3. Hydraulically – A metering ball or valve is used to block the flow of fluid. Fluid pressure increases when the ball is seated and decreases when the ball is unseated.

On-Off solenoids are used to allow fluid flow or block fluid flow but have no ability to create a variable fluid flow (variable fluid pressure). Pulse-Width Modulated (PWM) solenoids are used to create a variable fluid flow (variable fluid pressure). This is used to control fluid pressures, shift feel or shift quality, and control the slip rate of the torque converter clutch and other clutches inside an automatic transmission.

Questions for Teachers:
1. What are the three different ways a transmission solenoid must work?
2. Give an example of what an on-off solenoid is used for in an automatic transmission?
3. What does the solenoid click test indicate about the condition of the solenoid?
4. Can a solenoid pass the "click test", but still not operate properly?
5. According to the cutaway of an on-off solenoid view in the video, does the fluid exhaust when the solenoid is on or off?
6. Why are Pulse-Width Modulated (PWM) solenoids used in automatic transmissions?
7. What advantage does a PWM solenoid have over an On-Off solenoid?
8. How do PWM solenoids create a variable fluid pressure?
9. According to the graphs in the video, what does a 40 percent duty-cycle mean?
10. According to the graphs in the video, does zero amps of current equal a high or low fluid control pressure?
11. Tell me one thing you learned or found interesting in this assignment?

Weber State University (WSU) – Automotive Technology Department – Automatic Transmission Lab. A technical discussion of On-Off and Pulse-Width Modulated Solenoids in an automatic transmission. This video covers the basic operation and function of On-Off and Pulse-Width Modulated Solenoids in automatic transmissions. We teach current vehicle technologies to our automotive students at Weber State University and online. For more information visit:

This video was created and edited by John D. Kelly at WSU. For a full biography, see

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