Harsh Downshift

gchu69 · October 17, 2018

500 miles into 2019 SLT and started experiencing a clunking when coming to a stop. Doing some research, sounds like a harsh 3-1 downshift has been an ongoing issue with GM trucks. Took it to dealer and rep experienced it as well during a test drive. All tests and diagnostics came back normal and they told me it's the transmission adaptive function learning. Not buying this at all. Anyone experience this?

m3n00b · October 17, 2018

500 miles into 2019 SLT and started experiencing a clunking when coming to a stop. Doing some research, sounds like a harsh 3-1 downshift has been an ongoing issue with GM trucks. Took it to dealer and rep experienced it as well during a test drive. All tests and diagnostics came back normal and they told me it's the transmission adaptive function learning. Not buying this at all. Anyone experience this?

Is this the 8 speed? Sounds exactly like the issue I had with my 16.

Sent from my SM-G965U using Tapatalk

gchu69 · October 17, 2018

21 minutes ago, m3n00b said:

Is this the 8 speed? Sounds exactly like the issue I had with my 16.

Sent from my SM-G965U using Tapatalk

Yes the 8 speed.

m3n00b · October 17, 2018

30 minutes ago, gchu69 said:

Yes the 8 speed.

This is how I fixed it. After the C1 re-learn it was 100% better. Decided to do the C4 learn too to be 100% sure. Took about 30 minutes early one saturday morning when there was no traffic.

https://gm.oemdtc.com/6777/16-na-019-information-on-transmission-adaptive-functions-and-correcting-low-mileage-harsh-shifts-slips-or-flares-2016-2017-buick-cadillac-chevrolet-gmc

To Learn C1 (For 6-7 or 3-1 Shift)

Pressure Learns:

Note: It is recommended to utilize a road with a speed limit between of 30-45 mph (48-72 km/h) for this procedure.

Shift the transmission into 6th gear with the PRNDM in the M position. Obtain an engine speed between 1000 and 1600 engine rpm. Maintain this condition for a total of about 5 miles (8 km). Cruise control may be used and has been found to result in faster learning of the clutch values.

Volume Learns:
- Complete 15 light throttle 6-7 upshifts at approximately 15% throttle to further learn C1.

I also did this:

To Learn C4 (For 1-2, 5-6, or 7-8 Shift)

Pressure Learns:

Note: It is recommended to utilize a road with a speed limit between of 40-45 mph (64-72 km/h) for this procedure.

Shift the transmission into 7th gear with the PRNDM in the M position. Obtain an engine speed between 1000 and 1750 rpm. Maintain this condition for a total of about 5 miles (8 km). Cruise control may be used and has been found to result in faster learning of the clutch values.

Important: Application Specific Express & Savana Vans Pressure Learns:Perform 10 normal mode 7-6 coast down shifts (zero/light brake) to learn the C4 Return Spring.

Volume Learns:
- Complete 15 light throttle 1-2 upshifts at approximately 15% throttle to further learn C4.

Edited October 17, 2018 by m3n00b

Cmillerjr · October 18, 2018

When I first got mine, it did the same thing. Especially when rolling to a stop. I took it to the dealer with 250 miles, .there was no TSB, the said it may just be the transmission learning and may go away.

Sure enough, I’m a little over 1900 miles and it’s gone. It hasn’t done it for the last 1200 miles or so.

gchu69 · October 18, 2018

21 hours ago, m3n00b said:

This is how I fixed it. After the C1 re-learn it was 100% better. Decided to do the C4 learn too to be 100% sure. Took about 30 minutes early one saturday morning when there was no traffic.

https://gm.oemdtc.com/6777/16-na-019-information-on-transmission-adaptive-functions-and-correcting-low-mileage-harsh-shifts-slips-or-flares-2016-2017-buick-cadillac-chevrolet-gmc

To Learn C1 (For 6-7 or 3-1 Shift)

Pressure Learns:

Note: It is recommended to utilize a road with a speed limit between of 30-45 mph (48-72 km/h) for this procedure.

Shift the transmission into 6th gear with the PRNDM in the M position. Obtain an engine speed between 1000 and 1600 engine rpm. Maintain this condition for a total of about 5 miles (8 km). Cruise control may be used and has been found to result in faster learning of the clutch values.

Volume Learns:
Complete 15 light throttle 6-7 upshifts at approximately 15% throttle to further learn C1.

I also did this:

To Learn C4 (For 1-2, 5-6, or 7-8 Shift)

Pressure Learns:

Note: It is recommended to utilize a road with a speed limit between of 40-45 mph (64-72 km/h) for this procedure.

Shift the transmission into 7th gear with the PRNDM in the M position. Obtain an engine speed between 1000 and 1750 rpm. Maintain this condition for a total of about 5 miles (8 km). Cruise control may be used and has been found to result in faster learning of the clutch values.

Important: Application Specific Express & Savana Vans Pressure Learns:Perform 10 normal mode 7-6 coast down shifts (zero/light brake) to learn the C4 Return Spring.

Volume Learns:
Complete 15 light throttle 1-2 upshifts at approximately 15% throttle to further learn C4.

Appreciate it. Saw this online but wasn't sure if anyone had success with it.

gchu69 · October 18, 2018

13 hours ago, Cmillerjr said:

When I first got mine, it did the same thing. Especially when rolling to a stop. I took it to the dealer with 250 miles, .there was no TSB, the said it may just be the transmission learning and may go away.

Sure enough, I’m a little over 1900 miles and it’s gone. It hasn’t done it for the last 1200 miles or so.

Thanks. Had a "clunk" free day yesterday so hopefully it's gone.

gchu69 · October 22, 2018

On 10/17/2018 at 7:33 PM, Cmillerjr said:

When I first got mine, it did the same thing. Especially when rolling to a stop. I took it to the dealer with 250 miles, .there was no TSB, the said it may just be the transmission learning and may go away.

Sure enough, I’m a little over 1900 miles and it’s gone. It hasn’t done it for the last 1200 miles or so.

Did it happen to come and go? It stopped completely for a few days but started up again just today.

Cmillerjr · October 22, 2018

1 hour ago, gchu69 said:

Did it happen to come and go? It stopped completely for a few days but started up again just today.

It did, it was of and on. Sometimes it was worse than others. Sometimes I’d go a few days with nothing.

gchu69 · October 23, 2018

17 hours ago, Cmillerjr said:

It did, it was of and on. Sometimes it was worse than others. Sometimes I’d go a few days with nothing.

Ok thanks.

GMCustomerService · November 1, 2018

On 10/17/2018 at 10:22 AM, gchu69 said:

500 miles into 2019 SLT and started experiencing a clunking when coming to a stop. Doing some research, sounds like a harsh 3-1 downshift has been an ongoing issue with GM trucks. Took it to dealer and rep experienced it as well during a test drive. All tests and diagnostics came back normal and they told me it's the transmission adaptive function learning. Not buying this at all. Anyone experience this?

Hi, gchu69. Sorry to hear about this clunking concern. If you’re thinking about re-visiting your servicing GM dealership about your situation, I would be happy to work alongside them, to provide an additional layer of support. I hope to hear from you soon.

Anthony J.

eddiek · September 5, 2019

2019 duramax 1400 miles, when you down shift it feels like you get rear ended, shifting in general is just not smooth

mattsvtcobra · September 8, 2019

On 10/17/2018 at 11:41 AM, m3n00b said:

This is how I fixed it. After the C1 re-learn it was 100% better. Decided to do the C4 learn too to be 100% sure. Took about 30 minutes early one saturday morning when there was no traffic.

https://gm.oemdtc.com/6777/16-na-019-information-on-transmission-adaptive-functions-and-correcting-low-mileage-harsh-shifts-slips-or-flares-2016-2017-buick-cadillac-chevrolet-gmc

To Learn C1 (For 6-7 or 3-1 Shift)

Pressure Learns:

Note: It is recommended to utilize a road with a speed limit between of 30-45 mph (48-72 km/h) for this procedure.

Shift the transmission into 6th gear with the PRNDM in the M position. Obtain an engine speed between 1000 and 1600 engine rpm. Maintain this condition for a total of about 5 miles (8 km). Cruise control may be used and has been found to result in faster learning of the clutch values.

Volume Learns:

Complete 15 light throttle 6-7 upshifts at approximately 15% throttle to further learn C1.

I also did this:

To Learn C4 (For 1-2, 5-6, or 7-8 Shift)

Pressure Learns:

Note: It is recommended to utilize a road with a speed limit between of 40-45 mph (64-72 km/h) for this procedure.

Shift the transmission into 7th gear with the PRNDM in the M position. Obtain an engine speed between 1000 and 1750 rpm. Maintain this condition for a total of about 5 miles (8 km). Cruise control may be used and has been found to result in faster learning of the clutch values.

Important: Application Specific Express & Savana Vans Pressure Learns:Perform 10 normal mode 7-6 coast down shifts (zero/light brake) to learn the C4 Return Spring.

Volume Learns:

Complete 15 light throttle 1-2 upshifts at approximately 15% throttle to further learn C4.

On the volume learns, I am doing this after the pressure learn. So go the 5 miles and then speed up into the 6th gear, and use the + to go to the 7th? Just keep doing this last part over and over?

609dry · September 11, 2019

I have the same problem... harsh 3-2-1 down shifts .... problem seems most prevalent on warm days 85º + with trans temp 178º - 180º...... Started around 1700 miles went away because outside temps cooled off but then returned at 2900 miles on a 91º day

609dry · September 11, 2019

I have the same problem... harsh 3-2-1 down shifts .... problem seems most prevalent on warm days 85º + with trans temp 178º - 180º...... Started around 1700 miles went away because outside temps cooled off but then returned at 2900 miles on a 91º day

Edited September 12, 2019 by 609dry
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