Ashley P

Auto trans...adapt values

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Looking for info on GM transmission "adaptive learning" ,  scanner shows "TAP cells" (load cells) with values of positive or negative numbers representing pressure change from an "ideal" or "baseline"  (at least that's what I'm thinking, it's similar to fuel trim).   I've got a 2-3 shift flare and the TAP values are negative...it's as if the computer is commanding a soft/slipping shift and I can't find info from GM on how that TAP value is determined.  Can any tuner folks point me to some info?  (2007 4L60e)

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Looking for info on GM transmission "adaptive learning" ,  scanner shows "TAP cells" (load cells) with values of positive or negative numbers representing pressure change from an "ideal" or "baseline"  (at least that's what I'm thinking, it's similar to fuel trim).   I've got a 2-3 shift flare and the TAP values are negative...it's as if the computer is commanding a soft/slipping shift and I can't find info from GM on how that TAP value is determined.  Can any tuner folks point me to some info?  (2007 4L60e)

Just like fuel trims, commanded vs actual.

Ashley P likes this

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Thanks.

It appears the ECM calculates shift times and compares that value vs a desired time and forms a shift time "error", then adds or subtracts pressure to reduce that error..  I think the issue is with the calculation of error time.  Most good shifts are about .55 second long, yet some 2-3 shifts are much longer and yet the shift time will read under .5 second.  I don't wanna blame the input/output sensors because they're used for all shift times (and other gears work fine). Maybe some sorta voltage feedback when solenoids are changed for the 2-3 shift....who knows right now.  Customer's only car, and I've got other stuff, so it's supposed to be back Monday.

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Backstory:  This is the second transmission to shift like this.  The first trans never sifted correctly, and after cleaning/disconnecting MAF with no help, Jasper sent a warranty trans.

This second trans flared when first driven, but as the adapt values "learned" (a couple dozen 2-3 shifts later), it shifted great.  Customer brought it back a week later flaring on 2-3 again.  Jasper sent a tool to control the trans, trans works well when given commands.   But when the TCM still detects quick shifts when it's flaring and continues to back down shift pressure (according to negative adapt values).  Jasper wanted to blame the computer, but I swapped the TCM from a good shifting truck, still flares on 2-3.  Scan data looks OK when graphed.  No noticeable glitches.

Seems to be a yet invisible bad input to the TCM.  Could be:  bad speed inputs from trans, bad inputs from ECM.  No codes, no glitches...power probe it?  lol

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Backstory:  This is the second transmission to shift like this.  The first trans never sifted correctly, and after cleaning/disconnecting MAF with no help, Jasper sent a warranty trans.

This second trans flared when first driven, but as the adapt values "learned" (a couple dozen 2-3 shifts later), it shifted great.  Customer brought it back a week later flaring on 2-3 again.  Jasper sent a tool to control the trans, trans works well when given commands.   But when the TCM still detects quick shifts when it's flaring and continues to back down shift pressure (according to negative adapt values).  Jasper wanted to blame the computer, but I swapped the TCM from a good shifting truck, still flares on 2-3.  Scan data looks OK when graphed.  No noticeable glitches.

Seems to be a yet invisible bad input to the TCM.  Could be:  bad speed inputs from trans, bad inputs from ECM.  No codes, no glitches...power probe it?  lol

Negative numbers actually indicate it’s trying to raise pressure, not lower it.

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Posted (edited)

44 minutes ago, gammey4 said:

Negative numbers actually indicate it’s trying to raise pressure, not lower it.

????  I'm mucho confuso...earlier you said the adapts were like fuel trims.  And SnapOn data lists the adapt values as PSI.  How can a negative number of PSI relate to a higher pressure??

 

 

Edited by Ashley P

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Well, if an ideal PSI is X, and the value of the change from X is listed at negative 15, it would seem logical that 15 PSI is being removed from X.  A negative = reduction of PSI.  You're claiming it's opposite, correct?

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Well, if an ideal PSI is X, and the value of the change from X is listed at negative 15, it would seem logical that 15 PSI is being removed from X.  A negative = reduction of PSI.  You're claiming it's opposite, correct?

Yes. Shift adaptive values are a percentage to multiply against the pressure control solenoid current. So a negative 15 would reduce the current to the solenoid, thus increasing line pressure. In a “limp mode” scenario do you think gm would want max pressure or none?

Edit: and snap on probably uses a generic pid to display the data, That’s why you see psi.

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3 hours ago, gammey4 said:

 

 

Yes. Shift adaptive values are a percentage to multiply against the pressure control solenoid current. So a negative 15 would reduce the current to the solenoid, thus increasing line pressure. In a “limp mode” scenario do you think gm would want max pressure or none?

Edit: and snap on probably uses a generic pid to display the data, That’s why you see psi.

Well, it's a SnapOn Solus and the "adapt values" are listed as a PSI, and every time I add a negative number to X I get less than X.  lol   I know the "Tran X 2000" "scanner" that Jasper sent to control the trans read the pressure solenoid "duty cycle" backward from SnapOn, so maybe our failure to agree is based on the scanners/software we're using???

'"Would GM want max or no pressure in 'limp'?"   Well, I'd say max.  Zero amps to the pressure control solenoid gives maximum pressure.  Can you relate that to the adapt values?

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Well, it's a SnapOn Solus and the "adapt values" are listed as a PSI, and every time I add a negative number to X I get less than X.  lol   I know the "Tran X 2000" "scanner" that Jasper sent to control the trans read the pressure solenoid "duty cycle" backward from SnapOn, so maybe our failure to agree is based on the scanners/software we're using???

'"Would GM want max or no pressure in 'limp'?"   Well, I'd say max.  Zero amps to the pressure control solenoid gives maximum pressure.  Can you relate that to the adapt values?

You answered your own question. Unless it was shifting faster than commanded it wouldn’t reduce pressure. The logic is pretty simple, slower shift than commanded add pressure, faster take away. Your snap on is wrong. And I know you being an actual mechanic you verified real pressures with a gauge and aren’t solely relying on the sensors. That would have already told you that you have a leak in the third gear circuit most likely.

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11 minutes ago, gammey4 said:

You answered your own question. Unless it was shifting faster than commanded it wouldn’t reduce pressure. The logic is pretty simple, slower shift than commanded add pressure, faster take away. Your snap on is wrong. And I know you being an actual mechanic you verified real pressures with a gauge and aren’t solely relying on the sensors. That would have already told you that you have a leak in the third gear circuit most likely.

What about the SnapOn scanner is wrong?  

What if the TCM "thinks" it's shifting faster than commanded?  I believe that's what's happening.  The TCM measures a slipping/flaring shift at .3 of a second, yet a normal shift is .5 second.  The flaring shift is taking waaayyyy longer than the .5 second. 

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What about the SnapOn scanner is wrong?  

What if the TCM "thinks" it's shifting faster than commanded?  I believe that's what's happening.  The TCM measures a slipping/flaring shift at .3 of a second, yet a normal shift is .5 second.  The flaring shift is taking waaayyyy longer than the .5 second. 

The tcm uses rpm, input and output shaft speeds, to determine when a shift has completed. How would the tcm expect a rpm increase when shifting 2 to 3? And the snap on is using a generic pid to display a value. A generic pid will displace a value from anything without really looking into the specific math behind it.

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Still, if good shifts are measured at about .5/sec long, how can a slipping shift that OBVIOUSLY (to the driver) takes much longer be measured at .3/sec??   That does not make sense to me.  But, if that's what's happening, then every other goofy thing DOES make sense (the commanded reduction in pressure, the accompanying flare).

I thank you for though provoking replies.   Maybe I'm also fighting tunnel vision.   I'll try to regroup, doubt my previous thoughts, and come at it from your perspective that the computer is actually trying to shift harder.   (That runs me into the problem of why doesn't it add a little more pressure and stop the flare?)

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15 hours ago, gammey4 said:

 

 

Yes. Shift adaptive values are a percentage to multiply against the pressure control solenoid current. So a negative 15 would reduce the current to the solenoid, thus increasing line pressure. In a “limp mode” scenario do you think gm would want max pressure or none?

Edit: and snap on probably uses a generic pid to display the data, That’s why you see psi.

Well, just drove the truck, TAP values are carried out to the thousandth, so it makes sense that's a factor not a psi.  So I'm gonna bark up the tree from your perspective.  Many thanks!

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Well, just drove the truck, TAP values are carried out to the thousandth, so it makes sense that's a factor not a psi.  So I'm gonna bark up the tree from your perspective.  Many thanks!

What’s the year/model truck? I can post the trans files if you want to see them

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The jasper tech guy is trying to help me, but he's about as far behind me as I am behind you.  :smirk:   He's trying to tell me the MAF is the major input for shift firmness and they've seen MAFs cause a 2-3 flare.  How likely is a MAF to blame?

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I can't tell specific on that year or model, but on my CTSV the engine tune is highly important for the transmission tune.  The PCM calculates torque from a few things (I'm sure air flow is a big one) and tells the trans what pressure to use to hold that torque.  So, the jasper guy might be right.

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The tcm uses calculated load, tps, vehicle mph, input shaft rpm, to calculate when to shift. If you want to rule out the maf, take off the air intake tube and force it into speed density mode. Don’t just unplug the sensor, it still needs it for intake air temperature. If it’s unplugged it will default to -32 degrees (or somewhere around there) and run like crap.

If your maf was that far out you would see it in your fuel trims.

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Well, truck is gone for today.  But earlier I did disconnect it, engine ran fine, trans shifted hard.  PCS amp request was 0, so my assumption is it was in "limp mode" due to MAF open circuit.

I don't think fuel trims were out, but this project has stretched for weeks with an hour here, hour there.  I coulda missed that.   Because I have a MAF from my 07 5.3 afm Avalanche, I'm wanna plug it up and make sure it runs/shifts the same.

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Well, truck is gone for today.  But earlier I did disconnect it, engine ran fine, trans shifted hard.  PCS amp request was 0, so my assumption is it was in "limp mode" due to MAF open circuit.

I don't think fuel trims were out, but this project has stretched for weeks with an hour here, hour there.  I coulda missed that.   Because I have a MAF from my 07 5.3 afm Avalanche, I'm wanna plug it up and make sure it runs/shifts the same.

Maf disconnected won’t cause a limp mode. I run my truck in speed density, have for years.

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