What's the difference between M6 and D?

[Dale_K]

Does the 6 speed auto in my 2015 work differently in M6 compared to D?

 

I was noticing the V4 to V8 switchover squeak and put my truck in M5 to stop it from using V4 mode. I confirmed no more V4 on the DIC fuel economy display. Then I used the shift lever switch to put the truck in M6 thinking it would basically act like the truck didn't have V4 mode but still use high gear. But I found out M6 reactivates V4 mode.

 

So what is the point of M6?

[Oldbay]

I'm still coming up to snuff with the new units, but 6th is typically an overdrive gear. It probably reactivates V4 when it detects that you are not under load. You probably need to keep it in M5. It has to do with the torque converter---I think. It will detect that there is no excessive strain on the system and go back into efficiency mode. If the vehicle was under load it would likely stay in M6.

[Thomcat]

I'm still coming up to snuff with the new units, but 6th is typically an overdrive gear. It probably reactivates V4 when it detects that you are not under load. You probably need to keep it in M5. It has to do with the torque converter---I think. It will detect that there is no excessive strain on the system and go back into efficiency mode. If the vehicle was under load it would likely stay in M6.

X2 - V4 is likely used in combination with the torque convertor lockup in high gear to save another teaspoon of gas per tank.

[11bDad]

In the 6L80, fifth and sixth gears are both considered overdrive gears. Driving in M5 disables AFM, but it is active should you shift to M6 (only for that gear). I couldn't stand AFM, so I bought a Range AFM delete, but still drive in M5 & M6 simply because it shifts better, and Grade Braking is turned off. I learned more than I wanted about this transmission after my torque converter and pump went out at 10K miles. Four trips to the dealer to get it fixed.

 

Good info here:

 

 

[ChrisTronyxYocum]

In the 6L80, fifth and sixth gears are both considered overdrive gears. Driving in M5 disables AFM, but it is active should you shift to M6 (only for that gear). I couldn't stand AFM, so I bought a Range AFM delete, but still drive in M5 & M6 simply because it shifts better, and Grade Braking is turned off. I learned more than I wanted about this transmission after my torque converter and pump went out at 10K miles. Four trips to the dealer to get it fixed.

 

Good info here:

 

 

 

I'm not so sure about Grade Braking being off in M5 & M6 because if I put the truck into either of those gears and then press and hold the Tow/Haul button for 6 seconds and release, it tells me it disabled Grade Braking, not that it enabled it.

[11bDad]

 

I'm not so sure about Grade Braking being off in M5 & M6 because if I put the truck into either of those gears and then press and hold the Tow/Haul button for 6 seconds and release, it tells me it disabled Grade Braking, not that it enabled it.

Just going by what I've read here:

 

http://gm.oemdtc.com/5611/normal-mode-powertrain-grade-braking-feature-2013-2016-cadillac-chevrolet-gmc

 

3rd item under Activation : "No grade braking is available in Range Select Mode (Manual Shift Mode".

[ChrisTronyxYocum]

Just going by what I've read here:

 

http://gm.oemdtc.com/5611/normal-mode-powertrain-grade-braking-feature-2013-2016-cadillac-chevrolet-gmc

 

3rd item under Activation : "No grade braking is available in Range Select Mode (Manual Shift Mode".

 

So what I'm seeing is just a weird bug? Or is there a larger bug perhaps?

[Oldbay]

X2 - V4 is likely used in combination with the torque convertor lockup in high gear to save another teaspoon of gas per tank.

 

 

Exactly.

[jagabom (Esquire)]

OP, I don't think there is a point for it.

Jim

[davevinc1080]

I have been driving in M6 for a week or so and my fuel mileage is a fair bit better......around town and on the highways. I am confused. Also it feels like it is shifting a lot smoother and a lot less.

[Donstar]

Does the 6 speed auto in my 2015 work differently in M6 compared to D?

 

I was noticing the V4 to V8 switchover squeak and put my truck in M5 to stop it from using V4 mode. I confirmed no more V4 on the DIC fuel economy display. Then I used the shift lever switch to put the truck in M6 thinking it would basically act like the truck didn't have V4 mode but still use high gear. But I found out M6 reactivates V4 mode.

 

So what is the point of M6?

If you are not out of warranty, I would get the squeak fixed. The "D" mode works well in my truck and V4 mode is only noticeable by the readout on the DIC. The M mode and the tow/haul mode are nice features on these transmissions!

[Ozer]

I have been driving in M6 for a week or so and my fuel mileage is a fair bit better......around town and on the highways. I am confused. Also it feels like it is shifting a lot smoother and a lot less.

So when you start driving you just put it in M and then it shifts it as needed? and you drop it down the M5 if it gets to M6?

I havent played around with mine, V4 works fine in mine and hardly notice it but then again this is my first ever truck.

[MaverickZ71]

In the 6L80, fifth and sixth gears are both considered overdrive gears. Driving in M5 disables AFM, but it is active should you shift to M6 (only for that gear). I couldn't stand AFM, so I bought a Range AFM delete, but still drive in M5 & M6 simply because it shifts better, and Grade Braking is turned off. I learned more than I wanted about this transmission after my torque converter and pump went out at 10K miles. Four trips to the dealer to get it fixed.

 

Good info here:

 

 

Just watched the video for kicks. At the end was a simple 2-question quiz. I dunno jack about transmissions, but I got both questions correct. It was very disconcerting that 50% of the techs in the class got the proper transmission fluid question wrong and NONE of them got the 2nd question correct! The 6L80E is way complicated. And now GM is doing 10-speeds. All we really need is a good TH400 or 200r4. Gas mileage sux on a full sized truck anyway.

[davevinc1080]

So when you start driving you just put it in M and then it shifts it as needed? and you drop it down the M5 if it gets to M6?

I havent played around with mine, V4 works fine in mine and hardly notice it but then again this is my first ever truck.

 

 

I am just playing around with it too. I put it in M and before I leave either put it in M5 or M6. It will still work as a full auto transmission and you can shift if you want to (for speed control down a hill etc) Not sure if the M6 allows the truck to go into v4 or not. From what everyone is saying if you leave it in M5 then it will be locked in 8cyl, and M6 will still hit v4? I am not sure about this. I am enjoying driving around in M. my Drive D works great too....just trying to learn more about everything the vehicle can do.

 

The post above says only M6 gear is into v4, which can feel. COOL! dont need a tuner to stay in 8cyl

[jono20]

If you are not out of warranty, I would get the squeak fixed.

What's the fix for the AFM squeak?