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New problem with this 2012 Yukon XL 1500 Denali 6.2L. I really hate this truck! GREMLIN is back

So, you failed to say if this is a Afm, which I think it is. That depends on oil pressure and electrical inputs from the ecm, and it is riddled with problems.

Anyway, if your tach drops to Zero and seems like it shuts down (or jumping around 0-1500, 1500-3000) you have a bad ground (either on the engine or frame to body). This is very common. This would also set no code (the ecm thinks you shut it off, because it lost a ground.

If the tach drops to Zero slowly that’s a fuel problem. This might not set a code. I had a fuel pump relay do this, once again the ecm thinks you shut it down, so no codes would be set.

Quit throwing parts at it you are inducing more problems, first fuel or electrical go from there. Did I fail to mention CHECK YOUR GROUNDS…. Some one else said the same start there first. If you think that might be the problem (hint, hint) run a temp ground from the battery to the frame, engine and cab. Making sure they have a good contact (remove a little paint until you see metal). That would eliminate one side of the problem.

When you find the problem and it’s running good, get rid of the Afm it’s a problem waiting to happen. Sounds like it is happening now, a clogged oil screen under the oil pressure switch would cause this.
 
testdepth said:
I'm still having problems with this Yukon Denali 6.2L.

This morning after sitting all night my wife goes to an appointment. After normal cold start she started down the road at 45 mph and gets 5 miles from the house when the truck while running down the road starts chugging/choking back and forth and RPMs are going up and down. Truck felt like it would stall but didn't. She drove it back home and parked it. Truck did not have an engine code or code for anything. After warm up and engine at normal temp I used my TOPDON code reader to find no codes or check engine. I then took it to a dealership mechanic that has worked on GMs for 30yrs. He ran his reader and no codes or check engine. He did the relearn on the crank sensor again. He also checked for any updates to the ECM but there were none. Right now the RPMs cutout at 3500 and it's supposed to be 4000. I did it a few times by slowly pressing the foot pedal and watching the RPM climb. Once it gets to about 3500 it automatically reduces back to idle of 600 rpm. Truck is not reliable as is. Any ideas?

In the last few weeks I have replaced the following parts with new:
OEM AC Delco fuel pump
Negative battery cable
AC Delco MAF sensor
Crank sensor (did the relearn using my scanner and the dealer scanner)
Throttle body
Plugs and coil packs
Valve cover gaskets
EVAP Purge Solenoid
EVAP cannister

Help!
Click to expand...
Yeah ain’t great the problems all this Electronic on vehicles & other things it causes, not fun dealing with today’s vechiles . Seem be a lot more lemons in today’s automotive field . Hate for you
 
testdepth said:
My wife drove this truck 35 miles one way with no issues. On her way back home about 15 miles from home while driving 55 to 60 mph she hears a clunk sound, rpm gauge goes to zero, stabilitrack and traction warnings come on and both are stating they are off on the dash and the truck starts chugging so she pulled over. She let it set a few minutes and it started back up but check engine lights is on. She continued to drive it home and at about 5 miles from home it does the exact same thing again. I have never seen a problem like this.

I took this truck to a mechanic I know at a Chevrolet dealer. He has 30yrs experience with GM vehicles. He attached his scanner which tells him the crank sensor I put in the truck 1 month ago is bad. We also discovered one of the "oil filled motor mounts is bad".

I'm not sure if a crank sensor can cause all of what happened to the truck today or not?

If any GMC engineers read this I would like to say all of you are clowns and none of you must work on cars yourself.
Oil filled motor mounts, really?
Oil pressure sensor installed all the against the rear firewall and down 6 inches.
CAM sensor installed behind the crankshaft pulley that you have to remove to get to it.
Crankshaft sensor installed behind the starter.
Click to expand...

Just count your blessings that is not a 2025 model!
 
Greybeard said:
So, you failed to say if this is a Afm, which I think it is. That depends on oil pressure and electrical inputs from the ecm, and it is riddled with problems.

Anyway, if your tach drops to Zero and seems like it shuts down (or jumping around 0-1500, 1500-3000) you have a bad ground (either on the engine or frame to body). This is very common. This would also set no code (the ecm thinks you shut it off, because it lost a ground.

If the tach drops to Zero slowly that’s a fuel problem. This might not set a code. I had a fuel pump relay do this, once again the ecm thinks you shut it down, so no codes would be set.

Quit throwing parts at it you are inducing more problems, first fuel or electrical go from there. Did I fail to mention CHECK YOUR GROUNDS…. Some one else said the same start there first. If you think that might be the problem (hint, hint) run a temp ground from the battery to the frame, engine and cab. Making sure they have a good contact (remove a little paint until you see metal). That would eliminate one side of the problem.

When you find the problem and it’s running good, get rid of the Afm it’s a problem waiting to happen. Sounds like it is happening now, a clogged oil screen under the oil pressure switch would cause this.
Click to expand...
Thanks for your input and I'll address each:
It appears all Yukon Denalis with the 6.2L have the AFM so this one does.
I replaced the old ground cables with a brand new ground cable from the battery negative to the block and the frame. I cleaned the connection spots down to metal as well.
No fuel pump relay or fuse in this truck. It has a Fuel System Control Module up under the back of the truck.
I installed a brand new OEM AC Delco fuel pump a month ago.

I have not replaced the oil pressure sensor or the screen under it yet.

I drove this truck last night for about 20 minutes, speeds from 0 - 75, lots of turns and bumps. No issues at all.
I let this truck sit over night and drove it this morning cold until it warmed to normal temp of 210. It started normally and drove normally the entire 15 miles and back. No issues at all again.
No codes and no check engine.

Anyone use an AFM delete like this https://www.amazon.com/BOOST-AFM-DFM-Disabler-Mode/dp/B0D1T1FMJK/ref=cm_cr_arp_d_product_top?ie=UTF8
 
Check the grounds in yellow first then check the wires in blue up to the ecu. Use a analog meter instead of digital.

That’s where I would start, wire is not completely broken, maybe 1 or 2 strands left.
IMG_0236.jpeg
 
I would not replace anything else unless the problem returns. (ground cables hopefully corrected it).
As far as the AFM , deleting it does nothing to fix the problem with it. The lifters used with it are know to fail
and usually destroy cam and possibly engine with them.. To totally get rid of it you have to replace lifters with aftermarket ones , which is not cheap or easy. These motors are good motors but have there issues. The 1999-2006 is the best LS Motor because it does not have AFM. No need to replace oil pressure sensor or screen unless you are having oil pressure problems. Change oil often in these motors to help prevent problems
 
Well my wife just drove to Publix with no issues but this happens:

She got in the truck and started it to come home:

While parked the check engine comes on, Stabilitrak Disabled, Traction Control Disabled, Service Stabilitrak all come on and engine runs like its missing. She drove it home this way.

I put my scanner on it and it shows P0300 code. I brought up the misfire screen and shows cylinder 6 is misfiring. I just replaced all 8 coil packs so its possible one went bad.

I'm not sure why the stabilitrak and traction control would shut off though?
 
The ecu/ecm detected a variation in rpm (nbr 6 misfire) it tripped the stabitrak/traction control system put the old coil back in and reset the fault.

Run a abs test and clear the fault.

However that is not the problem you are having. That is an induced fault that was created by swapping in new coils, (the new one went bad).

Go back to looking at your grounds, I think you have a bad one going to your ecu/ecm that’s why it never tripped before. It thinks you are shutting it down, I.e. no recorded fault.

You really need a bidirectional scanner, it would help.
 
Greybeard said:
The ecu/ecm detected a variation in rpm (nbr 6 misfire) it tripped the stabitrak/traction control system put the old coil back in and reset the fault.

Run a abs test and clear the fault.

However that is not the problem you are having. That is an induced fault that was created by swapping in new coils, (the new one went bad).

Go back to looking at your grounds, I think you have a bad one going to your ecu/ecm that’s why it never tripped before. It thinks you are shutting it down, I.e. no recorded fault.

You really need a bidirectional scanner, it would help.
Click to expand...
I have a bidirectional scanner. I may not yet know how to use every feature of it.

 
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