Okay the next thing I want to show you has to do with transmission solenoids for the valve
body except these solenoids are the type that are either on or off so I have a solenoid right
here solenoids have to function in three different ways they have to work electrically and I have
a jumper wire I have a jumper pack connected here and I can this is as two terminals on this
solenoid I can command with power and ground and if you listen carefully you should be able
to hear the solenoid click when I connect power and ground so here we go you can hear that click
you can use a scan tool on most transmissions to command the solenoid to turn on and off when
the vehicle is parked with the engine not running and you listen for that click that
click tells you that it's working electrically and possibly mechanically and hydraulically
also and remember I said there are three ways that a solenoid has to work so electrically we
run current through this coil of copper wire right here it produces a magnetic field which
then either pushes or poles on a spring-loaded plunger that is going to block or unblock this
fluid passage right here on the end now that fluid passage would normally let hydraulic
fluid pressurized fluid come through it and then squirt out on these four sides right
here when the solenoid is off but when we turn the solenoid on it should block that pass he
did not let that happen well there's a way that we can test to see if the solenoid is working
like it should and it's with this special tool here and so I'm going to plug this solenoid in
we have a compressed air hose here and what I'm going to do is connect compressed air to it and
it will get real loud as it blows air through the normally-open so annoyed and then I will connect
power and ground to it and it should shut off that airflow and we should be able to see there
here that also so here we go it's going to flow through there comes a wire so it totally stopped
the flow of air just like it would stop hydraulic fluid when coming through so when we block the air
or the hydraulic fluid from coming through that fluid builds up pressure and it can push against
a spring-loaded valve in the valve body all the shift valve or whatever valve they want up to push
against because the valve will have a spring pushing it in one direction but as hydraulic pressure
builds from the solenoid being on it will push it back the other direction where it can so we have
different solenoids to control the position of these valves two-way valves to control upshifting
and downshifting of the transmission, so let's say in first gear the solenoid is off but to shift
the second gear we have to turn it on which would run apply pressurized fluid to the 1-2 shift
valve which would allow fluid to go to whatever clutch packs apply and hold different pieces of
the planetary gear set to give a second gear so we have solenoids that do that and these solenoids
are controlled by a computer and that computer bases its decision of when to turn these solenoids
on and off on all kinds of computer inputs the two main most important inputs are throttle position
whereas your foot on your accelerator pendant and the second one is vehicle speeds so it's
it's usually throttle position versus vehicle speed and then there are other factors involved
as well so I've got four more solenoids here we are going to test each one of them and see if
they are functioning as well as this solenoid that we just tested so this, I have worn off
the letter that is the letter A so here's letter B here let's check it or the ability to click first
it's clicking just fine put it in the tester hold it in place with the clip
next year to it it's allowing air to come through just like it should and now here's the electrical
so that one appears to be working as it should now let's try this one right here C let's see if
it clicks first yes it clicks let's put it in the tester hold it in place look air to it I was here
notice this one when we had power to it, although it clicked it didn't seal off the airflow
and so that solenoid is not working properly alright let's check this next one here D let's see
if it clicks, here you go, no clicking so if it doesn't click at all then it's not working as it should on
an on/off so on so let's do this last one E it clicks hold it in place it's an air to it
here comes the power, it is working like it should so we have some solenoids that work like they should we have
one that didn't work electrically at all we had one works it electrically but it bled the air out so
hydraulically wouldn't be working properly and then we had another one that was working fun so
these solenoids have to function all three ways electrically mechanically hydraulically in order
for the transmission to operate properly once again that's on these types of solenoids that
are on-off solenoids now if it's a pulse width modulated solenoid that you can't test it this
way you have to use a scan tool and the pressure gage a lot of transmissions to turn pressure up or
down so if you think about these on/off solenoids when they're off and fluid is flowing through it
freely there'll be no pressure building but when they're on we will get maximum pressure
but what if we didn't want maximum pressure and what if we didn't want zero pressure we wanted
something variable in between well that's where the pulse width modulated solenoids
come in handy and we can control by controlling the pulse-width signal the duty cycle how much
fluid goes through it based on how long we need the solenoid on versus how long we leave it off
as we cycle it some of these are around a thousand times a second they're turned on
and off but they vary how long they're on which is how long they're off in that time period and
that controls the position of the valve inside of here that controls the flow rate of the fluid
through and on later model newer transmissions they're getting away from these on-off only
solenoids almost all of them are pulse width modulated which means that we can control how
quickly the fluid goes through and goes to those clutch packs to shift gears for us and by being
able to control how quickly the fluid goes we can also control how each shift feels. is
that a nice smooth shift is that a hard shift is somewhere in between we can actually adjust
the shift quality as it's called by changing the pulse width modulation signal on the solenoid okay
you