PCS PWM Testing *solved* - now TCC issues

[flak monkey]

What's the best way to test the pressure control solenoid output is working properly?

I am suffering with maxed line pressures on my 4l80 and I am struggling to find the cause.

The PCS resistance is within tolerance, 4.2 ohms

I have verified I have 12volt to one pin of it on pin c and that I have a good connection all the way back to the mshift.

I have the diode and 4.7 ohm 10w resistor in the wiring loom per the manual.

Can I test the PWM output on the car with a gauge somehow to actually verify the solenoid is working?

[flak monkey]

Figured it out - started it up with a line pressure gauge hooked up and adjusted the pressure table and was able to alter the pressure OK.

I have more problems now - this transmission is driving me insane...

Having stalling issues when I come to a stop in D - like the TCC is locked. Had this problem before and fitted a Sonnax line to lube valve which seemed to fix it, but now it's back.

Also on my last drive I had some random, and worrying, downshifts...

Why did the transmission shift down to 1st from 3rd between 104 and 120 secs in the attached log?

The first shift was a manual one with my paddles - you can see the button presses in the log - but then there are 2 more changes down without me doing anything else.

It did this twice, I ended up changing up manually using the paddles to get it back in the right gear.

MSQ attached too...

I'm rapidly losing my patience with this transmission.

[flak monkey]

Turns out the problem with it stalling when stopping might have been because the TCC solenoid was being grounded by the megashift permanently. I unplugged the controller and the ground disappeared. So it's an internal issue with it.

So I have a problem with the circuit inside somewhere for the TCC output. For now I have pulled the pin out of the Amp connector to carry on testing and see if the problem resurfaces.

Anyone any idea where to start in checking the TCC circuit? I could just replace all the components in it I guess...

[gui67]

I also had the same problem once.
It was the transistor that was burnt. I replaced it and then it was OK. (I don't know why)
But I did not have the problem in first gear: the TCC could not apply, only on 2nd.

[flak monkey]

I removed the megashift and checked the resistance between the TCC output and ground pins on the AMP connector of the unit itself and got only 30ohms.

Opened it up and replaced all of the components in the TCC PWM circuit and rechecked and got an infinite reading as you would expect.

Question is what caused the components to fail?

Mine is a later transmission with a TCC solenoid with a resistance of 11ohms. Standard from '94 on. Having just done some reading on the subject, it's not recommended to run these in on/off mode as they are prone to overheating and frying the coils.

I expect this low resistance solenoid is what has caused failure of the TIP120 transistor by drawing too much current. If this is the case then I will have to use PWM for my TCC apply. Not a problem, but I thought I should be able to use on/off according to the 4l80 build pages.

GM actually PWM the solenoids all the time the TCC is engaged, so it looks like I'll need to add another diode in my wiring loom too...

[turbojim]

Thanks I have the same problem with the tcc will change the transistor and try again