[digitalgulby]

Hello forum friends. I’m a bit of a lurker and not a regular poster. I have been searching for this information and haven’t been successful.

I have a 17 ZL1 a10 w/ 25k miles, summer toy only with an occasional HDPE. Noticed lately that the 3-2 downshift in manual mode is unusually harsh. Also getting some violent low speed surges. I’m clearly out of warranty but any ideas on what this might be?

Is this the transmission, or the diff? Does it need a service?

[taylorforschool@gmail.com]

Especially the gears you are discussing has me worried. You should do some digging on the threads I have posted and the nightmare I went through with GM during Covid getting my repairs done under warranty. As much as many on the forums here would like to disagree with me, there are documented issues with the 10-spd across almost every GM platform. They aren’t very common but at this point I would say bulletproof is quite a stretch.

[digitalgulby]

Originally Posted by taylorforschool@gmail.com

Especially the gears you are discussing has me worried. You should do some digging on the threads I have posted and the nightmare I went through with GM during Covid getting my repairs done under warranty. As much as many on the forums here would like to disagree with me, there are documented issues with the 10-spd across almost every GM platform. They aren’t very common but at this point I would say bulletproof is quite a stretch.

Oh boy, that sounds a bit concerning. I’ll take a look.

[Megahurtz]

Did the battery recently die? If the TCM learning was reset then it will down shift rather harshly for a couple of drives.

[digitalgulby]

Originally Posted by Megahurtz

Did the battery recently die? If the TCM learning was reset then it will down shift rather harshly for a couple of drives.

Actually, yeah. Over the winter I put a new battery tender on it, and I foolishly didn't change the charge setting to 12v, it was set at 6v all winter.

Being the OE battery was ~7 years old I put a new one in.

I never noticed any problems before until this year. I didn't know that was a thing.

[CalgaryZL1]

With the several computers running this car, it can act like a baby with new teeth. Very finicky.

[Dynamical]

Does disconnecting the battery also reset the TCM learning?

[Bangkok_ZL1]

This is good to know....

[2023_ZL1-AUTO]

I had a similar issue when my battery died over the winter. I had it on a battery tender, but someone (I think my middle kid) unplugged the power stirp it was plugged into to charge a USB device! My car just didn't drive right the first two times I had it out. Even got a lot of scary warning message on the display like, rear axle disabled, body control module lost communication etc. etc. Then I got a fully charge on the battery over about a week long period and the 3rd time I drove it, it was as normal as could be.

[digitalgulby]

Originally Posted by 2023_ZL1-AUTO

I had a similar issue when my battery died over the winter. I had it on a battery tender, but someone (I think my middle kid) unplugged the power stirp it was plugged into to charge a USB device! My car just didn't drive right the first two times I had it out. Even got a lot of scary warning message on the display like, rear axle disabled, body control module lost communication etc. etc. Then I got a fully charge on the battery over about a week long period and the 3rd time I drove it, it was as normal as could be.

Sounds similar to me. When I did get it back running again it felt like the car was “stupid”. Pushing buttons didn’t work, I was wondering if the electronics were fried or something. It seems fine now. Very odd.

[Kamero6]

Originally Posted by Dynamical

Does disconnecting the battery also reset the TCM learning?

Yep, in my experience throttle response and TCM shift calibrations.

[Kamero6]

Originally Posted by digitalgulby

Sounds similar to me. When I did get it back running again it felt like the car was “stupid”. Pushing buttons didn’t work, I was wondering if the electronics were fried or something. It seems fine now. Very odd.

There are some volatile tables in the TCM and ECU. Once you disconnect power those tables reset on purpose.
ECU most probably adjusts the throttle curve a little bit, and TCM relearns the wear of the clutches/fluid. Basically calculates the position/delay where the clutches actually engage.

Some other cars have a learning procedure instead of this.

[Dynamical]

Originally Posted by Kamero6

Yep, in my experience throttle response and TCM shift calibrations.

Thank you. I guess I should stop disconnecting