Warning for using a 2017+ unlocked T87A from HP Tuners instead of using the stock one

I bought a "unlocked" T87A from HP tuners since I needed my car and couldn't ship my stock one out and not be able to drive my car. I ended up throwing a code for P27A7, which is the TCM is "Transmission Control Solenoid Valve 1 Calibration Incorrect". Now I'm not sure why it only trips the code for the #1 solenoid and not all of them, but the point is it looks like HP tuners does not flash the individual solenoid calibration data when they unlock a new TCM for you and program it to your VIN #.


Now the mystery about this is the service manual says the code is for "Incorrect" calibration and not "Missing". I have no idea how the TCM would ever figure out with confidence that your calibration data was "incorrect". As far as I know the 8L90 only has speed and pressure sensors as feedback, so it would have to have some preset table and logic that it could see with enough precision that the commanded current it was sending to the solenoids was not getting the correct pressure. There could be a million other reasons this could be true, not that someone forgot or flashed the wrong solenoid calibrations.


I think HP tuners does not calibrate this data for you when they program the VIN#, I just could not get a straight answer from support and it looks like they can't actually calibrate the solenoids.


Also if anyone would like a unlocked T87A let me know, seems like my only option now would be to pay to send my stock original TCM in to get unlocked and then pay to relicense it. Or either deal with a constant, pending check engine light, you cannot clear it. However, I did just find in the latest beta that P27A7 you can set to "No MIL Light" so im going to see if that at least turns off the check engine light.

Not sure if this is the same issue. I fired my truck up today and it had a check engine light for ?P27AB?. Only there on the hp tuners TCM. My stock TCM doesn?t throw the code. Both flashed stock, only the hp tuners one throws a code. Can?t clear it or shut it off. I?m in contact with them now about this. Assuming something isn?t right inside the hp tuners TCM.

It was my understanding that each solenoid is serialized and the TCM has to be programmed with them. If you replace your transmission for instance, the TCM needs to be updated with the new serial numbers. I dont know if you need that GM J computer for that or if it is something that HP tuners can somehow open up as a feature in the tuning program.

There is a guy on youtbe who talks heavily about the 8l90 and 8l45 (I think the main point of his video is doing a fluid change) but he goes into a lot of detail. He is a guy in a wheel chair if that helps the video search.

I have not seen this exact code and don't have my GM info at home with me. My guess is that the TCM needs to go through the learning process (even fastlearn) in order to control all of the processes properly. Once it has gone through the learning process a T87 can be used in different rigs without setting codes (though not very smoothly until it relearns the clearances, pressures, etc of the transmission that it is connected to). Only you can take your TCM through the learning process on your transmission.

This does not necessarily mean that the TCM was not prepared properly. Even a properly prepared PCM will set a code if the case learn (crank learn) is not done...pop in the old PCM, no code, new PCM, code....until it has learned about the motor....the TCM might just need to learn about the trans it has to control.

I've tried a relearn procedure with GM GDS and it still dosent help. The only options you have with GDS for that specific year model is the full relearn procedure and the induvidual clutch relearns. There is no process available for programming the solenoid serial numbers into the TCM as far as I know it has to be done with a TIS subscription, since you have to download the solenoid data directly from TIS servers straight into the solenoids, there is no possible way to program yourself.

Exactly right. If the TCM has not been properly loaded with solenoid data it won't be able to do much right. Hopefully I will have a chance to look into that code today. Maybe we can at least find out exactly what is not right.

I haven't noticed any change in shift quality, so maybe the right calibration data for the solenoids is in the TCM. It still dosent shift good enough for me, but I just think that's do to GM not caring about shift quality with the 8L90, im talking about the unnecessary hard low throttle shifts, clunks, jolts, bumps, and pushy shifts like the 8L90 likes to do.

The long learning process might be worth it for you. Basically it is just repeating and repeating shifts that are not to your liking until the computer learns how to apply everything properly. One thing I have found really true from GM's article (attached below) about the learn process, is the need to coast down with no brakes. Letting the vehicle slow down without applying the brakes for some reason lets the trans learn the right way to apply the downshifts. It seems to help with the 3-1 bump that everybody gets coming to a stop. I prefer to tune it out but the trick does help.

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cmitchell17a - Where are you from? If close to NW ohio I will flash your TCM with SPS. I have GM access and the MDI to do whatever you need. If you are close, that is.

Thanks for the offer but I'm about 10 hour drive from you. I've actually disabled the codes with HP tuners so I don't have to deal with seeing a MIL. I don't notice any difference in shifting, I think maybe the solenoid data did get programmed, but something else may be going on. To me my 8L90 has random clunks and didnt even shift right with the stock TCM. I think that's just the way GM wants their transmissions to shift and looking at some of the ways they tune the tables in the stock calibrations, random discontinuities, etc. It makes sense. On top of that you have all the backlash they put into the driveline it makes the clunking and diveability worse.

Yeah there's a lot of flak towards GM for the way the 8 speeds shift. Figured I would at least offer since I do have the ability. Maybe someone closer can get you taken care of. Good luck

If you swap TCMs to a new one hp tuners should send you directions on what’s needed to be done.. basically pretty simple and under special functions do TCM swap... whole thing takes about 3-4 min

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Originally Posted by Chrome_Rust

Yeah there's a lot of flak towards GM for the way the 8 speeds shift. Figured I would at least offer since I do have the ability. Maybe someone closer can get you taken care of. Good luck

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Disable converter lockup for 1-6 gears and the tranny will be nice and smooth. Best to leave 7 and 8 alone for best fuel mileage.

Yes, disabling lockup at zero throttle coast will help the rolling downshift clunks by letting the tie-up/torque reversal get absorbed through the unlocked torque converter. Besides the coasting downshift clunks, I haven't found leaving the TC unlocked to help much with the other random bad shifts. The most annoying part of the clunky shifts is the inconsistency of them, you never know when you're going to be ideling along through a parking lot or stop and go traffic and get a bang/clunk and hear the whole driveshaft and differential make a noise. The bad shifts mostly happen at very low throttle, rasing the shift times hasn't seem to help. I think the problem is more hydrualic I wouldn't think GM has some code buried in the TCM that's doing this on purpose but who knows. GM seems to think people don't care about low speed diveability. I feel like they could have implemented a throttle delivery dampener and a throttle follower in in first gear. All my GM vehicles I've had are almost undrivable at low speed in first gear stop and go traffic, you very carefully start pressing on the gas trying your best to avoid jerking everyone around, then all the sudden the engine revs up until all the excess slack is taken up and bam the slack is taken up and it slams forward, then the car in front of you stops so you let off the gas and your whole head gets thrown forward. This drives me insane.

Also I did the replace TCM function in the scanner and it gave me a warning saying something didn't work right and I may have to try it again.

Any real solution for this? I am having the same issue with a silverado that throws a p27a7 and p27a8 only after flashing the tcm with vcm editor. It will learn the solenoid data and be fine but after a flash it throws the codes. So far the only answer i have it a lengthy process to make the TCM relearn the solenoid data with a MDI tool after every flash.

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Originally Posted by meatbag

Any real solution for this? I am having the same issue with a silverado that throws a p27a7 and p27a8 only after flashing the tcm with vcm editor. It will learn the solenoid data and be fine but after a flash it throws the codes. So far the only answer i have it a lengthy process to make the TCM relearn the solenoid data with a MDI tool after every flash.

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Yeah it dosent make sense that its only for thoes specific solenoids, but how are you flashing the solenoid data? Do you have a TIS subscription? Or is there another way to do it?

great, just got my new one in the mail and i'm just now reading this. I'll let you know what I find.

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Originally Posted by GPGTP

great, just got my new one in the mail and i'm just now reading this. I'll let you know what I find.

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Watching this, since Im looking at an ATS-V...

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Originally Posted by Chrome_Rust

cmitchell17a - Where are you from? If close to NW ohio I will flash your TCM with SPS. I have GM access and the MDI to do whatever you need. If you are close, that is.

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I?m in Fort Wayne and once I get my ecm and tcm gonna needs security relearn. Help a brother out?

Find this modules folder and remove it placing it on your desktop.
Now re-do the entire process for the replacment TCM.
C:\Users\....\Documents\HP Tuners\VCM Scanner\Modules