rough shift 1st to 2nd: fast service learn

[persistent]

i've recently done a dod delete, and i also did a transmission fluid flush and filter change. the vehicle had the battery disconnected for long periods of time, and i experienced battery problems to the point i had to replace the battery a few days ago. i am experiencing missed/rough shifts from 1st to 2nd when driving now.

when i did the trans fluid flush, i followed the instructions about getting trans fluid temp up to 167-175 F then filling via the fill plug until it was dripping out. this process is no fun.

i've done some reading and watched some videos that suggest when you're having issues with rough shifting, you should do a "transmission fast service learn". afaict, this entails doing torque converter stalls to get trans fluid temp up to the same range you use for filling - 167-175 F - and then using a scan tool to initiate a fast service learn. this sounds relatively straighforward, but i've found very little information about how to properly execute the fast service learn. i have 4 scan tools that may support the service fast learn.

i suspect the battery being unplugged for so long or the battery problems led to the tcm losing its programming, so it's trying to do a slow adaptive relearn, which is going poorly.

i'm looking for advice on executing the fast service learn or similar procedures that would help fix the rough shift from 1st to 2nd.

 

[swathdiver]

@NickTransmissions

What do you think Nick?

 

[NickTransmissions]

i've recently done a dod delete, and i also did a transmission fluid flush and filter change. the vehicle had the battery disconnected for long periods of time, and i experienced battery problems to the point i had to replace the battery a few days ago. i am experiencing missed/rough shifts from 1st to 2nd when driving now.

when i did the trans fluid flush, i followed the instructions about getting trans fluid temp up to 167-175 F then filling via the fill plug until it was dripping out. this process is no fun.

i've done some reading and watched some videos that suggest when you're having issues with rough shifting, you should do a "transmission fast service learn". afaict, this entails doing torque converter stalls to get trans fluid temp up to the same range you use for filling - 167-175 F - and then using a scan tool to initiate a fast service learn. this sounds relatively straighforward, but i've found very little information about how to properly execute the fast service learn. i have 4 scan tools that may support the service fast learn.

i suspect the battery being unplugged for so long or the battery problems led to the tcm losing its programming, so it's trying to do a slow adaptive relearn, which is going poorly.

i'm looking for advice on executing the fast service learn or similar procedures that would help fix the rough shift from 1st to 2nd.

Check out my 6L80 Information thread, link is in my signature line...There's a link to fast-adapt relearn instructions you can download and follow....I believe the link is called 'Installation Procedures' - this all assumes you have a 6L80/90.

 

[persistent]

i used the cgsulit sc530, my cheapest scan tool, to do the fast service learn.

the shifting issue is substantially improved from earlier, but it still misses every so often. i will update after another few 100 miles of driving if it sorts itself out.

if the problem persists post-fast-learn, i will try a clutch learn for that shift in particular.

 

[NickTransmissions]

i used the cgsulit sc530, my cheapest scan tool, to do the fast service learn.

the shifting issue is substantially improved from earlier, but it still misses every so often. i will update after another few 100 miles of driving if it sorts itself out.

if the problem persists post-fast-learn, i will try a clutch learn for that shift in particular.

What do you mean by "misses"? Is the transmission skipping 2nd gear?

 

[persistent]

afaict, it's a rough shift from 1st to 2nd, where the rpms "flare" upwards during the shift and the tires chirp a bit. i'm not sure what the ideal way to confirm this would be, e.g. monitor the shifting using mdi2+gds2.

i checked the level for the trans fluid and it was a bit low (0.25-0.5 qt), likely as a result of my not having had the car close enough to level on the lift when i filled it originally. the fluid was still cherry red from my recent flush and fill.

my wife has put another several 100 miles on the vehicle and the rough shifts show no sign of subsiding. that said, i have managed to narrow down the trigger for the rough shifts - going from a stop straight to 1500 rpm or higher and sustaining it. as long as there is a short easing into the acceleration in 1st, the rpms can go up to 3k or higher in 1st without event.

since my wife has a bit of a lead foot, she can easily trigger the rough shift, but she's learning to modify her driving habits for the time being.

my guess based on reading some of your old posts, that fast service learn doesn't help much, that the problem persists after confirming the fluid level is proper, and this problem having appeared pretty abruptly (after repair work) versus gradually over time is that there is a problem with the valves.

i'd appreciate any pointers you can give regarding further diagnosis.

EDIT: forgot to mention this is a 2020 tahoe with 10L80 trans and 89k miles, and i see no related dtcs when checking with scan tool.

 

[persistent]

did some furthering reading and found a relevant section in the service manual titled "symptoms - automatic transmission". the service manual pdf i have only covers the 6 speed trans, but most of the general content is clearly relevant to the 10 speed trans. the details obviously change between the 6 and 10 speed trans.

i will do the road test procedure and see if i can spot anything notable on the gds2 live data. it does appear possible that this issue is related to the torque coverter, so the road test processes may help determine if that is the case.

i have had a look at the sonnax zip kit for 10L80 gen 1, and depending on whether this problem sorts itself out via transmission adapt and what i find during the road test process, i was thinking about installing it. the only part of the install process in the instructions that gives me a bit of pause is the last step, where you're supposed to cut the latch valves. i assume it would be acceptable to use a dremel tool to cut and chamfer the valve stems.

if i do decide to install the zip kit, i would get a vacuum pump and test plate setup to test the specified locations on the valve body both prior to and after installing the kit. my understanding is that if any of the vacuum tests fail, that indicates a loose fit between the respective valve and the valve body, and depending on the damage, this could require either replacing the valve or the valve body.

i called the local dealership to inquire about the cost and lead time for a replacement valve body, and i was told the cost is 772 usd with a core charge of *1000 usd* and there is a totally unknown lead time, with supposedly ~3k valve bodies already on backorder, presumably for the 10L80 gen2.

 

[persistent]

i believe i have a characterization of the valve solenoid behavior when the transmission slips after some observation with gds2.

when in 1st gear, i see shift pc solenoids 1, 3, and 5 at ~2200 kPa (rest at 0), and in 2nd gear, i see 1, 3, a 4 at ~2200 kPa. pressure on 5 drops to 0 as pressure on 4 ramps to 2200 kPa during the 1-2 shift. when the shift slips, i see a notch in the solenoid 4 chart where i would expect to see a smooth ramp up. the flat section after the notch upwards is where the slipping is occurring, and the shift completes shortly afterwards when the solenoid 4 pressure ramps up to 2200 kPa.

i am guessing the pressure values come from a sensor internal to the solenoid. based on a quick look, it is not easy to source a replacement individual solenoid or solenoid set, in case it is damaged.

any thoughts on what kind of failure this could be, e.g. bad solenoid, solenoid o-ring damage, or loose clip? any ideas on how to source solenoid replacement parts? the goal with replacement parts here is to minimize downtime and having to re-disassemble the valve body.