Pulling DFM fuses

BlancoSilverado · January 3, 2022

Alright everyone,

First went for a drive and verified that i can see the DFM activate, which i saw. i am using an Autel MP808

i pulled over shut off the engine pulled fuse 60 and 67 and started the engine back up. no CEL, no codes in any other module. hit the main road and pulled my foot off the pedal(still light pedal to keep speed, noticed that the DFM was activating. Pulling the fuses does NOT disable the DFM.

I **saw** that the hood status was on the DFM page, i pulled over popped the hood and verified that the hood was properly latched and continued, immediately the dash reminder came on(to tell you the hood is open) and DFM was still not disable.

Sorry guys i wish this would of worked. I wonder what those fuses actually do?

FYI i was that DFM is activated when you're off the petal and coasting it seems to default to pistons 1 &3.

Edited February 10, 2022 by BlancoSilverado
** added more info**

RedLT · January 3, 2022

4 hours ago, BlancoSilverado said:

Alright everyone,

First went for a drive and verified that i can see the DFM activate, which i saw. i am using an Autel MP808

i pulled over shut off the engine pulled fuse 60 and 67 and started the engine back up. no CEL, no codes in any other module. hit the main road and pulled my foot off the pedal(still light pedal to keep speed, noticed that the DFM was activating. Pulling the fuses does NOT disable the DFM.

I was that the hood status was on the DFM page, i pulled over popped the hood and verified that the hood was properly latched and continued, immediately the dash reminder came on(to tell you the hood is open) and DFM was still not disable.

Sorry guys i wish this would of worked. I wonder what those fuses actually do?

FYI i was that DFM is activated when you're off the petal and coasting it seems to default to pistons 1 &3.

Was really wishing it did the trick, but I guess that would be too easy. Thanks for verifying it.

kmeleon · January 4, 2022

Damn, really thought it disabled. Thanks for testing.

Silverado4x4 · January 4, 2022

Well let me throw this in there being the fuses are pulled the computer might be throwing the signal to activate the lifters thus seeing it on the scanner, but they are not being activated due to the fuses being pulled much like a light bulb removed from a socket, you turn the light switch on it sends the power to the socket but won't work due to no bulb. :dunno:

voided3 · January 4, 2022

47 minutes ago, Silverado4x4 said:

Well let me throw this in there being the fuses are pulled the computer might be throwing the signal to activate the lifters thus seeing it on the scanner, but they are not being activated due to the fuses being pulled much like a light bulb removed from a socket, you turn the light switch on it sends the power to the socket but won't work due to no bulb.

That's a really good point; the computer would still be sending the signal and the scan tool would pick it up, but there's no power to the solenoids (I assume) with the fuses pulled.

I know on our L84 5.3 truck with the 8-speed, DFM is painfully obvious if you maintain precisely 31 MPH on flat ground as that is prior to a transmission up shift point at 32 MPH (it sounds like a helicopter in the cab...). If someone with the same setup wanted to try this with and without fuses, that would be pretty conclusive for me.

I'm really tempted to try this myself, but I've already had four lifters replaced and I have extended component coverage on the engine as a result, so I'm a bit chicken to try anything that would potentially void that as I know it's going to happen again. This does have me hopeful, though, as it doesn't doesn't seem to set any codes when you pull the fuses, at least.

BlancoSilverado · January 4, 2022

3 hours ago, Silverado4x4 said:

Well let me throw this in there being the fuses are pulled the computer might be throwing the signal to activate the lifters thus seeing it on the scanner, but they are not being activated due to the fuses being pulled much like a light bulb removed from a socket, you turn the light switch on it sends the power to the socket but won't work due to no bulb.

That is a really good point. What we really need to find out is what are those fuses powering? I don't have access to a wire diagram.

voided3 · January 4, 2022

Ok, I tried it. Based on the fuel economy readings and tell-tale vibrations, DFM was still active in D with the fuses removed. I switched between L7 and D on a few low speed neighborhood roads and also cruised up to 65 MPH on the highway to try this out. Looks like I'm firmly in the "L7 for Life" club.

Deadstockpomp · January 17, 2022

I started the thread on the trailboss forum. I just wish we can figure out what the fuses do. If it does not disable it then what is the purpose of them? It just makes no sense

kmeleon · January 17, 2022

1 hour ago, Deadstockpomp said:

I started the thread on the trailboss forum. I just wish we can figure out what the fuses do. If it does not disable it then what is the purpose of them? It just makes no sense

Agreed, mine are still out.

Deadstockpomp · January 17, 2022

1 hour ago, kmeleon said:

Agreed, mine are still out.

I gave up I put mine back in and am driving l9 I guess

M1ck3y · January 19, 2022

Guys... I haven't really read any of this thread; but there's no fuse you can pull that will disable dfm. Dfm operation is controlled by the ecm, and can only be altered through tuning.

WeGone · January 19, 2022

10 hours ago, M1ck3y said:

Guys... I haven't really read any of this thread; but there's no fuse you can pull that will disable dfm. Dfm operation is controlled by the ecm, and can only be altered through tuning.

Added a Pulsar LT to disable mine.

M1ck3y · January 19, 2022

3 hours ago, WeGone said:

Added a Pulsar LT to disable mine.

Nice! I didn't know they managed to figure something out. But yes, that's still through tuning.

xtrythis1 · January 19, 2022

Interesting topic, shame this doesn't work. I have a Range OBD2 DFM disabler but for the first 5 to 10 miles it still allows DFM to activate which is annoying and not great for a cold engine.. I just leave my trans in L7 (8 speed) and keeps it from kicking on until i hit the 10ish mile mark on a drive. Once i hit around 10 miles or so I can put it in D and runs as it should on all 8 cylinders all the time... until i turn the truck off again then have to start the whole process over again. UGH

NOCO Boss · January 20, 2022

There is a lot of interesting information in this article. It explains that equipment/wiring/etc. for the DFM can be present, but if the vehicle has RPO YK9 (was built without DFM) the ECM can’t activate it. I guess this explains why someone without DFM still has the fuses in the block.

https://gm-techlink.com/?p=14558