Performance shift not activating?

dbs1 · 05-08-2026, 06:05 PM

2018 ZL1 A10. Was at the road course last Nov and at the drag strip in March and car was upshifting and the marvelous downshifting then no problem.

It sat for 6 weeks while a gm tech after hours replaced the radio modules and cables (salvage title theft recovery) where it sat weeks on end not being run and eventually the battery kept going dead and I put a new one in.

Down to the dealer to get the radio programmed where it sat another 6 weeks without the tech there getting the radio programmed and with the last road course and drag events till fall today and tomorrow, I grabbed it a few days ago where it had to be jumped to start.

At the road course it would upshift but not down shift in auto. In manual it would downshift and upshift. Tried it multiple times at the track and on the street hammering it as it upshifted several times then jammin on the brakes and still no auto downshift.

Took it to the tuner and he could find nothing so far to solve it. Ideas???

ZLRob · 05-08-2026, 10:38 PM

Performance shift is typically a PCM exclusive thing that requires nothing but input from the APP to turn on. Aside from a potentially bad pedal that is not registering two tap in track mode, I'd actually be fairly inclined to assume that you are having some sort of PCM or some sort of a communication issue between modules. Especially if you needed a jump to start it.

How's the actual health of the battery and what sort of battery are you using?

dbs1 · 05-09-2026, 12:32 AM

Quote:

Originally Posted by ZLRob

Performance shift is typically a PCM exclusive thing that requires nothing but input from the APP to turn on. Aside from a potentially bad pedal that is not registering two tap in track mode, I'd actually be fairly inclined to assume that you are having some sort of PCM or some sort of a communication issue between modules. Especially if you needed a jump to start it.

How's the actual health of the battery and what sort of battery are you using?

This battery is new as of 6 weeks ago before it went to the dealer and sat for 6 weeks and had to be jump started to load in trailer. I left it on the charger all day yesterday and it started all day today but that was I and the tuners thought was the last 3 months of being run down and 1 battery completely bad may have something to do with it.🤷*♀️

ZLRob · 05-09-2026, 10:14 AM

Quote:

Originally Posted by dbs1

This battery is new as of 6 weeks ago before it went to the dealer and sat for 6 weeks and had to be jump started to load in trailer. I left it on the charger all day yesterday and it started all day today but that was I and the tuners thought was the last 3 months of being run down and 1 battery completely bad may have something to do with it.🤷*♀️

Yeah battery being run down never helps things. Make the jump to a lithium if you can. These cars benefit so much from it, especially as power hungry as they are. Traditional technology doesn't really do them any favors because of the huge parasitic draw that they naturally have.

dbs1 · 05-10-2026, 07:06 PM

I’ve had 2 of these cars and this is a new issue I’ve not seen.

Good news is that before putting it in the trailer last night in Phx at a track rental in over 100 degrees I did get it to break into the 10’s. Bad news is, it’s still not downshifting in auto🤷*♀️

05-08-2026, 06:05 PM	#1
dbs1 Drives: 2017 ZL1 Join Date: Aug 2020 Location: Lakeside, Az Posts: 513	Performance shift not activating? 2018 ZL1 A10. Was at the road course last Nov and at the drag strip in March and car was upshifting and the marvelous downshifting then no problem. It sat for 6 weeks while a gm tech after hours replaced the radio modules and cables (salvage title theft recovery) where it sat weeks on end not being run and eventually the battery kept going dead and I put a new one in. Down to the dealer to get the radio programmed where it sat another 6 weeks without the tech there getting the radio programmed and with the last road course and drag events till fall today and tomorrow, I grabbed it a few days ago where it had to be jumped to start. At the road course it would upshift but not down shift in auto. In manual it would downshift and upshift. Tried it multiple times at the track and on the street hammering it as it upshifted several times then jammin on the brakes and still no auto downshift. Took it to the tuner and he could find nothing so far to solve it. Ideas???

05-08-2026, 10:38 PM	#2
ZLRob Super Stock Drives: Chevrolet Camaro ZL1 Join Date: May 2022 Location: Concordia Posts: 1,004	Performance shift is typically a PCM exclusive thing that requires nothing but input from the APP to turn on. Aside from a potentially bad pedal that is not registering two tap in track mode, I'd actually be fairly inclined to assume that you are having some sort of PCM or some sort of a communication issue between modules. Especially if you needed a jump to start it. How's the actual health of the battery and what sort of battery are you using? __________________ 2017 Red Hot ZL1 A10 - Apex ARC-8's, 305/ 325 PS4's, DSX 9.06 12% lower, Griptec OE upper, NGK HR7 Ruthenium plugs, Nostrum 25+ injectors, XDI Goliath HPFP, Katech dual in tank LPFP, Katech oil pump, LME tensioner, DOD delete, LT1 big fuel cam, Jokerz ported blower, MPI lid, GMS hood extractor bracket, Granatelli SS plug wires, Cordes LTR reservoir, DMS T-stat housing, 186* LS3 T-stat, Borla X pipe, Black Widow Angry Housewife/ Corsa NPP mufflers, BMR engine mounts, Banks iDash, Lithium Battery, AEM X- Series, HP Tuners, E85, 16.5 psi 758 HP/ 804 TQ

05-10-2026, 07:06 PM	#5
dbs1 Drives: 2017 ZL1 Join Date: Aug 2020 Location: Lakeside, Az Posts: 513	I’ve had 2 of these cars and this is a new issue I’ve not seen. Good news is that before putting it in the trailer last night in Phx at a track rental in over 100 degrees I did get it to break into the 10’s. Bad news is, it’s still not downshifting in auto🤷*♀️

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