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I’ve been absolutely losing my mind with this issue. Let me try to explain
01 s10 4.3 auto

:replaced shift solenoids. Ignition. Ignition switch. Checked wires. Took the negative battery terminal off all night.

if I clear all codes to all modules and get in the truck and go it drives completely normal. But almost immediately when i turn the truck off and back on it will go 1-2-3 but gets stuck in 3rd. Even if I stop it stays in 3rd. Live data shows trans starting in 1st once hits 2nd the 1-2 solenoid turns off and will not turn back on.
live Data showing no short to ground or voltage (How could it when it shifts normally until restarted after clearing of codes)

I think it’s a module issue based on the fact if I clear just the p0785 code it does nothing. The truck will still start off in 1st then 2nd then 3rd but will get stuck in 3rd. And then throw code.
But if I clear all the modules it drives normally for the time being. And I mean I 1-2-3-4. Go to park back to drive. Can manually put it in 1st and back to drive and it will
Go 1-2-3-4. All seen on live data.

I thought it was an ignition issue based on a post I seen on this forum but it did not help me.
 

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Randy
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825 Posts
I’ve been absolutely losing my mind with this issue. Let me try to explain
01 s10 4.3 auto

:replaced shift solenoids. Ignition. Ignition switch. Checked wires. Took the negative battery terminal off all night.

if I clear all codes to all modules and get in the truck and go it drives completely normal. But almost immediately when i turn the truck off and back on it will go 1-2-3 but gets stuck in 3rd. Even if I stop it stays in 3rd. Live data shows trans starting in 1st once hits 2nd the 1-2 solenoid turns off and will not turn back on.
live Data showing no short to ground or voltage (How could it when it shifts normally until restarted after clearing of codes)

I think it’s a module issue based on the fact if I clear just the p0785 code it does nothing. The truck will still start off in 1st then 2nd then 3rd but will get stuck in 3rd. And then throw code.
But if I clear all the modules it drives normally for the time being. And I mean I 1-2-3-4. Go to park back to drive. Can manually put it in 1st and back to drive and it will
Go 1-2-3-4. All seen on live data.

I thought it was an ignition issue based on a post I seen on this forum but it did not help me.
P0785 is a 3-2 pwm downshift solenoid fault code. NOT a 1-2 or 2-3 shift solenoid. You should be able to measure 10-15 ohms resistance at pins "E" & "S". If it is more or less, you have a faulty 3-2 downshift solenoid. They are all fed 12v @ pin "E", the computer supplies the ground at pin "S" for the 3-2 downshift solenoid.

Here is a reprint of ATSG's P0785 diagnosis sheet. It should help.
 

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