Driving in L9 and DFM

[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.

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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.