Hitting rev limiter in drive
Drifting
Joined: Feb 2023
Posts: 1,357
Likes: 1,120
Where is this adaptive learning feature documented? I know about driver influenced gear selection "Aggressive driving will influence both the upshift and downshift points in all modes......Criteria which have influence are: driving mode, accelerator, brakes, lateral, and longitudinal loading......Changes in gear selection behavior due to aggressive driving can include: ‐ Downshifting early with higher rpm’s during aggressive braking (i.e. entering a corner) ‐ Altering upshifts while experiencing lateral acceleration ‐ Not upshifting when the accelerator is released to avoid unnecessary shifts if the accelerator is re-applied ‐ Recognizing sporty driving and anticipate upcoming corners with the appropriate gear selection entering and exiting." But the vehicle will exit this feature and return to normal operation after a short time when spirited driving is no longer detected.
There is also some re-programming of the transmission control module if the module or transmission or some transmission components are replaced. That procedure calls for "Transmission Control Solenoid Valve Characterization Programming". "The solenoids in this transmission require unique performance characteristic data in order to function at maximum efficiency. This data is programmed and stored in the vehicle transmission control module (TCM). When a transmission assembly, TCM, solenoids or clutch are replaced during service, the performance characteristic data for the solenoids must be retrieved from a web server oecloud repository and reprogrammed into the TCM." The description involves obtaining a specific transmission identification number and retrieving data from the cloud - does not sound like it is "learning" the transmission - but rather looking up previously stored data that is specific to that transmission. The process will also "read the VIN from the engine control module (ECM) using the multiple diagnostic interface (MDI) and then retrieve the applicable genealogy data tree from the cloud. This data tree accesses the original characterization data so that it may be updated with the new component information. The system acquires characterization data for the given TUN/PUN via the cloud and updates the genealogy tree. The TCM is updated with the correct solenoid characterization data, and the cloud is updated with the new genealogy relationship." This sounds like GM maintains an exact record of what your car has, and had.
It would not surprise me if there is some adaptive learning in the transmission (other than the driver influenced gear selection) but I can't find any documentation about that.
There is also some re-programming of the transmission control module if the module or transmission or some transmission components are replaced. That procedure calls for "Transmission Control Solenoid Valve Characterization Programming". "The solenoids in this transmission require unique performance characteristic data in order to function at maximum efficiency. This data is programmed and stored in the vehicle transmission control module (TCM). When a transmission assembly, TCM, solenoids or clutch are replaced during service, the performance characteristic data for the solenoids must be retrieved from a web server oecloud repository and reprogrammed into the TCM." The description involves obtaining a specific transmission identification number and retrieving data from the cloud - does not sound like it is "learning" the transmission - but rather looking up previously stored data that is specific to that transmission. The process will also "read the VIN from the engine control module (ECM) using the multiple diagnostic interface (MDI) and then retrieve the applicable genealogy data tree from the cloud. This data tree accesses the original characterization data so that it may be updated with the new component information. The system acquires characterization data for the given TUN/PUN via the cloud and updates the genealogy tree. The TCM is updated with the correct solenoid characterization data, and the cloud is updated with the new genealogy relationship." This sounds like GM maintains an exact record of what your car has, and had.
It would not surprise me if there is some adaptive learning in the transmission (other than the driver influenced gear selection) but I can't find any documentation about that.
Okay, you can use a scan tool to tell the trans ECU to 'fast adapt'. What this does is it clears the keep alive memory - this is learned data, and start over learning how the trans shifts in response to the base calibration commands and implement learned changes faster than normal for a preset period of time - usually based on ignition cycles.
All modern day trans controls have this feature in one form or another. In a production car, when a transmission responds and completes a commanded task like an upshift or downshift varies slightly from one car to another. The ECU has to have the ability to modify the timing of its commands based on when it sees a specific task completed, otherwise, you would have enormous problems getting a fleet of mass produced vehicles to drive properly.
Melting Slicks
Joined: Nov 2012
Posts: 3,163
Likes: 686
From: SUFFIELD CONNECTICUT
I do not believe that, The first time I asked my car to do a WOT in drive to test redline shift points, the car never hit the rev limiter during any WOT self shift in drive.. The car has been consistant from day one and 7000 miles later, shifts right at 6400 RPM each and every gear.
Race Director
Joined: Mar 2007
Posts: 11,376
Likes: 8,532
Thanks! And, now that I know the name of that function, I can find it in the Service Manual, and here is what it does:
"Description
The learn procedure performs a series of individual clutch applications which allows the control module K71to learn initial clutch apply pressures.
The control module uses the learn values for clutch control and timing of shifts.
When to Perform the Procedure
Note: Failure to perform this procedure may result in poor system performance, DTCs being set, or customer dissatisfaction.
This procedure is required when the following component has been repaired, replaced, removed, or serviced:
- K71 Transmission Control Module
- T12 Automatic Transmission Assembly
- Any condition/repair related to the following: Shift Quality
- Calibration Update or Software Update
- Clutch Assembly or Torque Converter Assembly"
Ya know, I thought I had seen this before, but I just could not find it, 'til you provided the name. And yes, I agree, it certainly implies that there is a "non-fast" learn that might take place over time as the transmission shifts during driving. Thanks again for that information.
"Description
The learn procedure performs a series of individual clutch applications which allows the control module K71to learn initial clutch apply pressures.
The control module uses the learn values for clutch control and timing of shifts.
When to Perform the Procedure
Note: Failure to perform this procedure may result in poor system performance, DTCs being set, or customer dissatisfaction.
This procedure is required when the following component has been repaired, replaced, removed, or serviced:
- K71 Transmission Control Module
- T12 Automatic Transmission Assembly
- Any condition/repair related to the following: Shift Quality
- Calibration Update or Software Update
- Clutch Assembly or Torque Converter Assembly"
Ya know, I thought I had seen this before, but I just could not find it, 'til you provided the name. And yes, I agree, it certainly implies that there is a "non-fast" learn that might take place over time as the transmission shifts during driving. Thanks again for that information.
Last edited by Andybump; Nov 9, 2023 at 07:20 AM.
Drifting
Joined: Feb 2023
Posts: 1,357
Likes: 1,120
I have not seen the C8 trans calibrations, but ordinarily, there are an enormous number of parameters and values the ECU looks at for controlling transmission functions. You would have to have a good understanding of how a transmission functions, generally speaking, to make sense of the control system. Just like the engine control system has adaptive ability to learn things like fuel and spark, so does the trans control system with regard to how fast it engages oncoming and offloading clutches and how fast it ramps on or off clutch engagement looking at things like slippage, torque input, oil temp, pressure slopes, timers etc..... What abilities are built into the C8 control system I do not know, but the software must be pretty advanced.
If a C8 keeps hitting the rev limiter an automatic mode (not manual), then a full diagnostic evaluation has to be made to find out why this is happening. If nothing is found in a diagnostic check, I would disconnect the battery to clear the keep alive memory and start over with the baseline factory calibration. There are limits on what adaptive learning can do. It cannot, for example, compensate for a unit with an internal mechanical problem.
If a C8 keeps hitting the rev limiter an automatic mode (not manual), then a full diagnostic evaluation has to be made to find out why this is happening. If nothing is found in a diagnostic check, I would disconnect the battery to clear the keep alive memory and start over with the baseline factory calibration. There are limits on what adaptive learning can do. It cannot, for example, compensate for a unit with an internal mechanical problem.
Race Director
Joined: Mar 2007
Posts: 11,376
Likes: 8,532
I added a little more info to post 25 about that fast learn procedure - I think it gives additional insight in to what it does, because it mentions the consequence of not doing it, and lists the conditions and/or component replacement that require the procedure.
When to Perform the Procedure
Note: Failure to perform this procedure may result in poor system performance, DTCs being set, or customer dissatisfaction.
This procedure is required when the following component has been repaired, replaced, removed, or serviced:
- K71 Transmission Control Module
- T12 Automatic Transmission Assembly
- Any condition/repair related to the following: Shift Quality
- Calibration Update or Software Update
- Clutch Assembly or Torque Converter Assembly"
When to Perform the Procedure
Note: Failure to perform this procedure may result in poor system performance, DTCs being set, or customer dissatisfaction.
This procedure is required when the following component has been repaired, replaced, removed, or serviced:
- K71 Transmission Control Module
- T12 Automatic Transmission Assembly
- Any condition/repair related to the following: Shift Quality
- Calibration Update or Software Update
- Clutch Assembly or Torque Converter Assembly"
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Advanced
Joined: Feb 2023
Posts: 78
Likes: 20
From: SoCal
Have the cars at Ron Fellows Racing School tweaked? I accidentally hit the fuel shut a couple times at 7000 RPM.
The engine would just DIE until the revs were lowered and then it went on happily with NO issues.
I drove the same car 2 full days & no worries
The engine would just DIE until the revs were lowered and then it went on happily with NO issues.
I drove the same car 2 full days & no worries
Instructor
Joined: Oct 2022
Posts: 170
Likes: 53
So, I thought I imagined it the other day but I was able to duplicate it a couple times today. When in drive in sport mode going about 15-20 and I pin the throttle, when the car shifts from first to second it smacks the rev limiter before shifting it actually makes me lurch forward in my seat.
Have any of you experienced this?
Have any of you experienced this?
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 34,949
Likes: 12,362
From: NE South Carolina
!
Hmm, one possibility I have not seen mentioned and happened to me often!
Drove ONLY in Manual Mode for the 1st month getting over every DD for 62 years, including 5 prior Vettes, being a standard shift. I make a 90 degree turn from the stop sign at the end of the rural road I live and often accelerate aggressively to merge into heavy packs of traffic going ~70 mph on the 4-lane divided highway at the end of that road. Upshift paddle is out of position and 1st gear hits Rev Limiter at 35 mph in the blink of an eye. No fun groping to find the upshift paddle as all fuel shuts off and traffic coming up fast behind.
So, I switched to Z-Mode Power set to Track. It drives as I was in Manual Mode and as I drove my two C7s. BUT it is smart enough to upshift all by itself!
BUT after making a left hand turn about 100 yards down the highway, I turn onto another rural road with no shoulder to slow. So traffic doesn't have to slow significantly for me I apply the brakes aggressively and it downshifts from 5th to 4th than 3rd in the blink of an eye just before I turn right. If just driving causally don't use a lot of throttle after the turn and it quickly upshifts.
Now where the OP may have done what happens to me IF there is little traffic and I am in MY Mode. On the highway the car may shift to 6th before I make the turn onto the other rural road. So similar to what I always did with my standard shifts I pulled the downshift level several times to downshift to 3rd before turning while braking moderately. With modest throttle after I turn expect it would upshift as it does in Z-Mode. BUT doesn't! Because I'm NOT in Drive MY Mode! I pulled the downshift paddle and for ~10 seconds it's in Manual Mode. If I had accelerated at WOT I would be at Redline in a few seconds. Then it would NOT shift by itself, it's waiting for me to pull the upshift paddle. If I don't Rev Limiter!
May not be the case but like I forget, so might the OP.
Drove ONLY in Manual Mode for the 1st month getting over every DD for 62 years, including 5 prior Vettes, being a standard shift. I make a 90 degree turn from the stop sign at the end of the rural road I live and often accelerate aggressively to merge into heavy packs of traffic going ~70 mph on the 4-lane divided highway at the end of that road. Upshift paddle is out of position and 1st gear hits Rev Limiter at 35 mph in the blink of an eye. No fun groping to find the upshift paddle as all fuel shuts off and traffic coming up fast behind.
So, I switched to Z-Mode Power set to Track. It drives as I was in Manual Mode and as I drove my two C7s. BUT it is smart enough to upshift all by itself!
BUT after making a left hand turn about 100 yards down the highway, I turn onto another rural road with no shoulder to slow. So traffic doesn't have to slow significantly for me I apply the brakes aggressively and it downshifts from 5th to 4th than 3rd in the blink of an eye just before I turn right. If just driving causally don't use a lot of throttle after the turn and it quickly upshifts.
Now where the OP may have done what happens to me IF there is little traffic and I am in MY Mode. On the highway the car may shift to 6th before I make the turn onto the other rural road. So similar to what I always did with my standard shifts I pulled the downshift level several times to downshift to 3rd before turning while braking moderately. With modest throttle after I turn expect it would upshift as it does in Z-Mode. BUT doesn't! Because I'm NOT in Drive MY Mode! I pulled the downshift paddle and for ~10 seconds it's in Manual Mode. If I had accelerated at WOT I would be at Redline in a few seconds. Then it would NOT shift by itself, it's waiting for me to pull the upshift paddle. If I don't Rev Limiter!
May not be the case but like I forget, so might the OP.
Last edited by JerryU; Nov 19, 2023 at 11:51 AM.