Driving in L9 and DFM

[NBonn21]

Greetings all

Has anyone confirmed if driving in L9 will disable DFM?

I haven't been able to find anything on the forums and haven't noticed whether it works or not . I have tried it but can not confirm for sure seeing that there is no indicator stating such. Plenty of older trucks that do but nothing on the newer vehicles with the 10 speed transmission

Until Range Technologies come out with a plug in to disabled DFM its my opinion this may be the best way to help prevent the dreaded lifter failure issue.

I have called Range and they cannot confirm if this will actually happen for the late model Tahoe/Yukon vehicles. Anybody hear anything else on this?

 

[olyelr]

Do these new rigs not notify you when they drop down to 4 cylinder mode? There was a little light on the dash in her last ‘16 denali, and it was kind of obvious when it did it anyway.

Well, on my ram, there is an indicator on the dash when it goes into 4 banger mode, not to mention it is obvious when it slips into that mode anyway. And, if i put the trans in the highest manual gear setting it will prevent dfm from kicking in altogether. Tow haul does it as well (but you get the different shift characteristics that comes along with going that way).

 

[Micahsd]

Do these new rigs not notify you when they drop down to 4 cylinder mode? There was a little light on the dash in her last ‘16 denali, and it was kind of obvious when it did it anyway.

Well, on my ram, there is an indicator on the dash when it goes into 4 banger mode, not to mention it is obvious when it slips into that mode anyway. And, if i put the trans in the highest manual gear setting it will prevent dfm from kicking in altogether. Tow haul does it as well (but you get the different shift characteristics that comes along with going that way).

No, I wish they did notify when it’s engaged.

 

[Reddevil96]

I can confirm on my 2021 XL Denali that L1-9 disable DFM. DFM does its normal operation in L10 and D. Drivability and power are far more consistent in L9 or less around town or slower traffic on the highway, and I am now using L6-L9 90% of the time.

 

[SSGUNNER]

I can also confirm L9 works and I’ve done this on my RST. With my exhaust setup it sounds very nice also wish. Personally I like to lean back when I drive so the actual setup and buttons are a bit of a stretch and not fluent. Wish we had paddle shifters instead but you can’t have your cake and eat it too. So I use it once in a while when I am feeling froggy.

 

[NBonn21]

Well I am glad to hear that, I will be driving in L9 almost always from now on.
My Denali was built on May 18th outside of the dates specified for the lifter failure but unfortunately I don’t have to much confidence in that timeline.

I love this rig but the reason I purchased this as my retirement vehicle was to travel the country and being left stranded a few thousand miles from home is not very appealing.

 

[Reddevil96]

I can also confirm L9 works and I’ve done this on my RST. With my exhaust setup it sounds very nice also wish. Personally I like to lean back when I drive so the actual setup and buttons are a bit of a stretch and not fluent. Wish we had paddle shifters instead but you can’t have your cake and eat it too. So I use it once in a while when I am feeling froggy.

Current pictures of the new Sierra show paddle shifters on the steering wheel. Would make for a nice upgrade swap onto yukons.

 

[SlimIm17]

I have a stock 2021 Tahoe Z71 5.3 L84, and just starting driving in L9. Wow, what a difference. I drive slow - - over the last 7,000 miles, I averaged 19.2 MPG driving in D. Too soon to tell how much driving in L9 will impact MPG (but saving gas isn't the reason to deactivate DFM).

In L9 the transmission upshifts later in the RPM band and stays in a lower gear when coasting...kind of like sport mode, or when hill descent activates. Also, noticed the auto stop/start feature doesn't kick in. Can't say for certain all 8 cylinders are on all the time, but it definitely feels that way.

 

[Blackhawkscrna]

I know I’m going to regret asking, but what is L9?

 

[Buffalown]

I know I’m going to regret asking, but what is L9?

I'm glad I'm not the only one lol

 

[Toomanyhobbies]

It's the idea of hitting the "L" button on your gear selector and then putting the "+" button until you get to 9, which locks the trans out of overdrive.

 

[drmoose]

I'm glad I'm not the only one lol

I’m not certain, but I am assuming they are meaning using the low/ shift buttons on the selector panel, and keeping it in gear 9, instead of the “D” button (where it will goto 10, and everything is automatically shifted).

 

[Buffalown]

I’m not certain, but I am assuming they are meaning using the low/ shift buttons on the selector panel, and keeping it in gear 9, instead of the “D” button (where it will goto 10, and everything is automatically shifted).

is there any downside to always driving like this, i.e. harder on the transmission or anything like that?

 

[Blackhawkscrna]

Thanks, that’s what I was assuming, just trying to wrap my head around “low” 9, lol.

 

[SlimIm17]

I'm glad I'm not the only one lol

Instead of "D", shift into "L" for low gears. In my model, you have to shift into D, then push L to enter low 1, but then push the "+" button 8 more times to be in "L9". You can adjust the highest gear the transmission will shift into, 1-10. My Tahoe has 10 speeds. Driving in L9 (or L7 or L-whatever), seems to turn off AFM/DFM so all 8 cylinders as always firing.

 

[SlimIm17]

is there any downside to always driving like this, i.e. harder on the transmission or anything like that?

More gas consumption. Over the last 300 miles, averaging 16-17 MPG when I was getting 19.2 before. Don't know the impact on the transmission.

 

[Matt Wilson II]

More gas consumption. Over the last 300 miles, averaging 16-17 MPG when I was getting 19.2 before. Don't know the impact on the transmission.

I want to congratulate you one getting 19.2 mpg. I've never seen a number that high with my Tahoe. Lol

 

[SlimIm17]

Thanks. I drive slow (or used to before L9) and coast a lot.

 

[Matt Wilson II]

Thanks. I drive slow (or used to before L9) and coast a lot.

View attachment 365247

I just took a 250 mile, round-trip today and used L9. I sh*t you not, my economy improved. I can't understand how eliminating a fuel-saving measure would save fuel, but it did. Mind you, I take these trips frequently. I went from 16.2 avg to 18.6. The majority of the trip was 74 mph on cruise. The truck was a lot smoother as well. I wish an actual GM engineer could chime in on this subject. I'm perplexed.

 

[Micahsd]

Curious on fuses 60 and 67 in the engine fuse block. They claim to be for AFM even though the 21’s and newer have DFM.

Some of the guys on the Sierra/Silverado forums have been pulling those two fuses to disable DFM on their 2019+ pickups with the 5.3. It sounds like on the 5.3 it works, but the 6.2 will run rough and those with the 5.3’s reported better engine response but wasn’t able to fully confirm it was truly disabled. I figured a code or service engine light would be set, but multiple users on those forums claimed no messages/alerts were seen.

I was just curious if anyone with a 5.3 has tried pulling those fuses and had good results.