VT Auto problem shuddering / power button

[Oley]

My VT commodore used to shudder when accelerating, suddenly the shuddering stopped, but now it is like the power button is stuck. I have put it down to "stuck power button", holds in gear longer, I know what the power button does, so i don't want a discussion on that. I want to know how it works in the transmission. The power switch connects to the Power Train Control Module, but then where ?? Occasionally it goes back to normal, but then the shuddering starts, i'm thinking sticking spool / solenoid or something. The power button clicks on/off, the light goes on/off, but makes no difference. For trouble shooting purposes, where does the signal go after the PCM.
Cheers

 

[NeddyBear]

I to have know idea what the Power button does and in our 8 years have never pressed it.
My thinking is why put any extra strain on the old girl than is really needed.

 

[WHCapriceHBD]

Power button sends the open/closed contact signal to the PCM.

The PCM then uses the on or off signal to control the shift solenoids in the transmission in a way that holds gears longer, or not.

In this scenario, we have pressed the Power Button ON:

PCM detects ON signal from button.

PCM swaps into "Power mode" shifting- begins telling electronic shift solenoids in gearbox "You're going to hold longer. I want you engaged until X RPM point is reached" etc.

PCM also tells lockup converter it is going to lock earlier and it will stay locked more often.

The Power button signal travels no further than the PCM. That is where it stops. At that stage the PCM is controlling the solenoids in one fashion or another, as well as the lockup converter.

The button is not the issue you need to be chasing. It is just a simple mechanical latching button and if unplugging the wires on the bottom of the button does not change anything, that proves its not a sticking contact inside the button, etc.

You need to look at the PCM, hook up a diagnostic laptop or Tech2 and verify that the shift solenoids are working as intended, and the lockup torque converter is working as specified.
My money is your shuddering is a result of a sticking solenoid in the gearbox or a bad lockup converter in the gearbox.
Long story short, replace the gearbox. The 4L60E is cheap and easy to find. Yours has an internal fault and is not going to get better.

 

[Oley]

That sounds about right, I called it "stuck power button" as I didn't know how to explain it otherwise. Are the Solenoids able to be accessed from the sump ??? Replacement transmission might be cheap, but don't the the history of it , so if sticking solenoid is accessible , might pay to have a look.
Cheers

 

[SavVYute]

Sounds like the vehicle has gone into limp home mode.
Have you had a 'check engine ' light illuminate?

 

[Oley]

Only just recently has the check engine light stayed on after startup for about 1-2 minutes, then goes out. Doesn't come on any other time.

 

[SavVYute]

If the light has come on it will have thrown a diagnostic trouble code that can be read.
That's the best place to start. Don't go replacing parts or transmissions just yet.

 

[Oley]

Problem has been going on for about a month, light only about a week. Can you read a fault code with the shorting method when the light is not on, or do you need a diagnostic reader.

 

[greenacc]

Try the paper clip method if you know how and see what pops up. Codes are stored for a looong time so will still be there to read.