2-1 downshift at a stop

BrewTown

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Hoping someone can shed some light on what to look for. This is my 4R100 in my '00 Excursion. I rebuilt the trans about 30k ago, with 327,500 on it now.
When the trans fluid is warm, it doesn't always downshift from 2nd to first at a stop. Sometimes giving a little more fuel gets it to downshift, but not always. Under 100° everything seems to operate normal. Plowing, meaning shifting from reverse to drive always goes into 1st.

I'm assuming something is getting stuck, and increased pressure gets it moving, I'm just not sure what. I do need to do a fluid change, and I will be removing it to swap the converter. This issue did seem to start after the converter had I believe a stuck stator, cooking the fluid after long freeway stints.

I do have a couple VB mods, and line pressure mods when I rebuilt it, and everything operated flawless until after 20k+ miles.

1 time I did get 2 codes, P0781 and P1715, both about that shift. That was only 1 time over at least 5k miles of intermittent issues. Usually my CTS2 just says it's in 1st, then switches to second when no shift occurred, which tells me it's mechanical and not commanded.🤷‍♂️
 

BrewTown

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Okay, so would that send the code each and every time? Or once over hundreds of times?
I'll look into this so I know if that solenoid acts on a valve, or not. My thought was it's one of the sliding valves that is getting stuck in the bore for one reason or another, which is why an increase in line pressure with throttle can force compliance.
Thanks Mark.
 

Mark Kovalsky

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That may be your thought, but it isn't what's happening. The solenoid is stuck. It needs to be replaced. The ONLY way that code can set is if the solenoid is stuck.

The code indicates that the inductive signature of the solenoid is showing that the armature in the solenoid isn't moving when it is commanded. It is possible that with higher pressures it will move. The PCM checks this every time it commands the solenoid. It resets the counter for the code each time it detects the solenoid didn't move.
 

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