DFM disabler released

[Kpwweb]

jfoj, appreciate your insight and my first thought was also battery or low voltage issue, but it was towed to the dealer and I have to assume they checked the charging system and battery as it was showing the same codes while in service and being diagnosed. Once they saw the module on the ECM, they pulled it and all codes gone. Picked it up on Saturday and module is enroute back to Range for testing/replacement. Tahoe running fine since. In all honesty, for what it does, and the inconvenience it "may" have caused is just not worth re-installing, especially on my wife's daily driver. I will definitely update this thread if these codes reappear or similar issues arise.

I would not assume the dealership checked the starting system.

I also agree with jfoj. The factory batteries are junk. I usually have to replace them within two years. At least on the last two Tahoes, when they start acting flakey, new battery goes in. One even tested “good”, but did not have staying power. It would fall flat in the cold. Good battery will solve a myriad of issues.

 

[jfoj]

The problem with a factory battery is it is always older than the vehicle. So on a 2023 model year vehicle, some may think since we are in 2025 the battery is less than 2 years old. Understand a 2023 model year vehicle could have a Sept 2022 build date. If this is the case the battery was built before Sept 2022. Who knows if it was built in Aug 2022 or April 2022? So it is possible the battery could be 3 1/2 years old on a 2023 model vehicle at this point, pretty much as End Of Life IMHO! Then you figure we are into the Winter/cold months depending on where the vehicle is located. The cold weather reduces the capacity of the battery and if the battery capacity is already compromised due to age, you have a problem on your hands.

Then with any vehicle, it sits around and the battery is always discharging. Lots of starts moving from the plant, to the transporter, of the transporter, around the dealer many times for PDI and so forth.

Also understand these charging systems are designed to have the alternator shut off when the engine is running. If for some reason when the engine started and the cranking Voltage dropped too low during last start before the messages popped up and the vehicle went into Limp mode, then this make total sense. When the available Voltage drops too low during engine cranking, modules fail to properly communicate and all sorts of gremlins show up.

If it is a vehicle my wife regularly drives and/or hauls kids, I would be getting her a new battery for Christmas. She may not appreciate it, but TRUST ME, you will in the long run!!

 

[nick14226]

The problem with a factory battery is it is always older than the vehicle. So on a 2023 model year vehicle, some may think since we are in 2025 the battery is less than 2 years old. Understand a 2023 model year vehicle could have a Sept 2022 build date. If this is the case the battery was built before Sept 2022. Who knows if it was built in Aug 2022 or April 2022? So it is possible the battery could be 3 1/2 years old on a 2023 model vehicle at this point, pretty much as End Of Life IMHO! Then you figure we are into the Winter/cold months depending on where the vehicle is located. The cold weather reduces the capacity of the battery and if the battery capacity is already compromised due to age, you have a problem on your hands.

Then with any vehicle, it sits around and the battery is always discharging. Lots of starts moving from the plant, to the transporter, of the transporter, around the dealer many times for PDI and so forth.

Also understand these charging systems are designed to have the alternator shut off when the engine is running. If for some reason when the engine started and the cranking Voltage dropped too low during last start before the messages popped up and the vehicle went into Limp mode, then this make total sense. When the available Voltage drops too low during engine cranking, modules fail to properly communicate and all sorts of gremlins show up.

If it is a vehicle my wife regularly drives and/or hauls kids, I would be getting her a new battery for Christmas. She may not appreciate it, but TRUST ME, you will in the long run!!

Wonder if there’s any decent battery tester that could be purchased, without breaking the bank, to routinely check battery health? I bought one from Amazon for 30 bucks, haven’t tried it yet, but it’s a small handheld device so unlikely it can properly apply a load to the battery for a proper load test.

 

[jfoj]

That tester checks Voltage and internal resistance which is a decent test, however, $30 tester is not the best quality. A internal resistance tester and load testing is best.

You can get the local auto parts store to test the battery for free, but I have seen problems with their testing. Usually operator error or bad software. If they test the battery and tell you a 2-3 year old battery is at 100% capacity or higher, there is a problem with the tool configuration or the software. I tend to condemn a battery at 75-80% of it's rated capacity.

Batteries are consumables, so any hint of a problem, I replace them. I also have a number of higher end battery testers I use a few times a year to track battery health and I also put a maintenance charge on the batteries a few times a year as well

 

[fondupot]

I promised a long time ago in this thread that I would log some ECM data with my scan tool with and without the Range DFM module installed. Well I finally had a reason to remove the Range module this weekend (truck went to dealer for the FPCM replacement recall) and I took that opportunity to log some data with the Range module off the vehicle. There was so many data points I could have logged using my scan tool, I settled on a very simple metric that really shows when DFM is active vs. when DFM is deactivated. See screen shots below.



These first two screenshots are logged on a short trip with the Range Module removed. This is driving normally around town where I live. As you can see there are thousands of counts of DFM turning on per cylinder. I like seeing the last two data points, Distance with Cylinder Activated and Distance with Cylinder Deactivated. I guess I forgot to screenshot the data for cylinders 6,7,8, but they showed the same data, with a few thousand counts per cylinder like you see on cylinders, 1 thru 5.





These next few screenshots are with the Range Module Installed. I did a similar route, just around town where I live. You can see there are zero counts of cylinder deactivation on all cylinders. Meaning the Range Module is doing what it says.

 

[Marky Dissod]

... finally had a reason to remove the Range module this weekend (truck went to dealer for the FPCM replacement recall),
and I took that opportunity to log some data with the Range module off the vehicle. There was so many data points I could have logged using my scan tool,
I settled on a very simple metric that really shows when DFM is active vs. when DFM is deactivated. See screen shots below ...
These first two screenshots are logged on a short trip with the Range Module removed. This is driving normally around town where I live.
As you can see there are thousands of counts of DFM turning on per cylinder. I like seeing the last two data points,
Distance with Cylinder Activated and Distance with Cylinder Deactivated. I guess I forgot to screenshot the data for cylinders 6,7,8, but they showed the same data,
with a few thousand counts per cylinder like you see on cylinders, 1 thru 5.

One of the chief goals of Dynamic Fuel Mgmt (originally Dynamic Skip Fire) was to minimize cylinder temp variations.
With Engine Half@$$, over a long enough service life, the part-time cylinders spend more time cooling off, thus wearing out faster than the full-time cylinders,
eradicating the MpG benefits over time as the full-time cylinders do more work dragging the lazy cylinders along for the ride.

DSF/ DFM constantly changes up which cylinders are taking incredibly short breaks, so no cylinder ever really cools off, so all 8 cylinders wear uniformly.

One of the few goals Cylinder Confusion actually manages to achieve, still best to disable / delete ...

 

[machete31]

Update: December 31st wife left at 5am to go to the gym, low temp in S. Louisiana that morning was 33F, upon starting Tahoe, multiple codes...she took my truck to the gym. I started it later that morning, around 8am and no codes, just check engine light. Let it idle for a while and shut it off, started back up around 10am no codes running fine. Conclusions: 1) Range module was NOT malfunctioning, nor caused previous issues 2) My confidence in the module is much better than my dealer service department.

Unfortunately, I don't have any idea exactly what the issue was as we had decided a few months back that at the end of the year to trade the Tahoe in, which we did on the 31st at a different dealer, though 99% probably battery.

 

[nick14226]

Update: December 31st wife left at 5am to go to the gym, low temp in S. Louisiana that morning was 33F, upon starting Tahoe, multiple codes...she took my truck to the gym. I started it later that morning, around 8am and no codes, just check engine light. Let it idle for a while and shut it off, started back up around 10am no codes running fine. Conclusions: 1) Range module was NOT malfunctioning, nor caused previous issues 2) My confidence in the module is much better than my dealer service department.

Unfortunately, I don't have any idea exactly what the issue was as we had decided a few months back that at the end of the year to trade the Tahoe in, which we did on the 31st at a different dealer, though 99% probably battery.

Thanks for providing the update, I was curious!

 

[jfoj]

A weak battery makes a lot of sense. As the temps drop, battery capacity decreases. Low cranking speed and Voltage can and will cause cold start misfires with Fuel Cut Off to protect the catalyst. I have seen this for years with BMW's and bad batteries. The other kiss of death is to start the engine in cold temps and move it in the vehicle in the driveway and shut the engine off. This can fuel wash the cylinders and wet the spark plugs with fuel and cause misfiring on the next engine start. I have seen and even had this happen to me many times. If below 50-60F, if I start an engine, I let it run at least 5-10!minutes before shutting the engine off

Cold Start fuel enrichment can be a big problem if the engine does not run for a while.