Buick 3.8 Transaxle shift help!!!

skipnrocks · Mar 14, 2019

I played with this today and got a little info not sure if it will help. I see on the reader where the shifter is in fourth. I can see it go into 3rd second and first when I move the lever.

I noticed that shift solenoid turns from on to off just prior to shifting into second, so I assume that it gets the call from the computer to shift turns the solenoid off and then it shifts. Then as I accelerate I dont see the 2-3 solenoid of turn off, and I assume this is why it is not shifting up from there?

If this is accurate What is my problem?

LightBnDr · Mar 14, 2019

The "current gear" display is the PCM commanded gear

skipnrocks · Mar 15, 2019

LightBnDr said:
The "current gear" display is the PCM commanded gear

So if that never goes to 3 or 4 does that mean the computer isn't calling for the upshift

LightBnDr · Mar 15, 2019

Correct. All you really need is "transmission output controls" so you can manually command a gear change

Then you can probe harness with it running on jack stands to be sure the signal is being sent.

Without that ability, your problem is gonna be hard to pin point. About all you can do is get it on stands and run that sucker almost redline and watch output speed.

If it never reaches the 2-3 3-4 speed parameters then the pcm won't command it

If it does reach it, then you gotta figure out why the pcm is not commanding it.

If all this sounds stupid for a kids a rig, then pull the valve body and make it full manual. Be done

skipnrocks · Mar 15, 2019

Nope doesn't sound dumb at all. With all the gear reduction from the trans axle and the acles coupled with the need to be user friendly for the littles I'm happy to trouble shoot the crap out of it.

Do you happen to know at what speeds the command should come for 3rd and 4th?

TBItoy · Mar 15, 2019

did it shift before you swapped PCMs?

skipnrocks · Mar 15, 2019

So I got Max 52mph at .73tps in second gear. I think my to wants a way higher speed to upshift. I know yellow with is the 2-3 solenoid in the harness. Maybe I can splice in a pig tail and ground it and see if it shifts up.

skipnrocks · Mar 16, 2019

So I spliced into the solid yellow/blk wire with a spice connector and then grounded it to chasis. It didn't appear to shift into third. The obd reader didn't indicate a shift and didn't indicate turning the solenoid off. But then again maybe it wouldn't indicate turning it off if it didn't call for it?!

Did I do it correctly to manually initiate a shift?

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LightBnDr · Mar 17, 2019

What's the solenoid command supposed to be during a 1-2 then a 2-3 shift ?

1-2 off 2-3 on ? Then 2-3 off and 1-2 on?

Asking because I'm wondering if the 2-3 is off during a 2-3 shift rather than on. Then you would just want to pull the pin from the harness to get a 2-3 shift

skipnrocks · Mar 17, 2019

2-3shift is solenoid a-off solenoid B-off

The fourth is a-on and b-off

skipnrocks · Mar 17, 2019

Is there a way to do any electrical testing prior to swapping out the solenoid? IE> shouldnt some current come through the solenoid 2-3 wire that is intended to be grounded?

Is it possible to have the plug in up side down? I appears on the pic above the plug arrow and shift wire are on the bottom side, but I have it plugged in so the arrow is up, since it makes sense to me. I do get trans temp and other data on the scan tool so I assume this isnt the case. but hey gotta double check stupid...

skipnrocks · Mar 17, 2019

I came across a thread they said if you unplugged the harness from the tranny it would have help rule in or out the b solenoid because it will only run in third gear. So I did this and it looks to have worked. It looks like I'll be pulling the tranny apart this week

LightBnDr · Mar 18, 2019

Don't pull that trans apart yet. Stay with me goose

skipnrocks · Mar 18, 2019

LightBnDr said:
Don't pull that trans apart yet. Stay with me goose

You were spot on and saved me hours of moving cross members. It was in fact a computer issue, and the computer not breaking the circuit to turn off the solenoid. I snipped the wire from the solenoid to the computer and it immediately shifted to third.

Talked to the computer guy he is now on board that this is a computer issue and is going to burn me a new one to help differentiate if it is a defective computer or simply incorrect values for the trans to shift.

With that wire bypassed I can now go a whopping 35 mph instead of 21 at redline.

skipnrocks · Mar 18, 2019

TBItoy said:
did it shift before you swapped PCMs?

Sorry I missed this. I never got to test it with the other pcm, it was corrupt from the beginning and the engine wouldn't run.

ranger11 · Mar 18, 2019

Good info in here even though ill prob never need it.

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skipnrocks · Mar 18, 2019

ranger11 said:
Good info in here even though ill prob never need it.

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For sure, I spent probably 15 hours searching and reading on this and there isnt a lot of info, probably because there is a million reasons it can go wrong and most people just take it to a shop to get it done.

skipnrocks · Apr 3, 2019

So big shout out of thanks to Lightbender for saving me from having to pull my transmission apart.

Lots of troubleshooting and turns out the drivetrain is not from an 01 which is what I was told. Its from an 04. In 2003 they changed the transmission and pcm so they wouldnt communicate quite right.

I havent verified for 100 percent but Have been told that with the new 04 pcm and new programming. But for the first time I have some good hopes. Sounds like we just need to refine the shift speed/rpm paramters for what we use it for and torque converter lockup and should be ready to roll to moab.