3 transmission codes on startup

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dkad260

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2012 Denali 147K miles

Yukon drives perfect, no shifting issues, I drove home from work and parked it. Came back 8 hours later I did a remote start and the engine started then immediately shut off, I figured a fresh CEL.

I restarted with the key then pulled these codes. Does this sound like a loose connection somewhere? Also throwing up the bat signal to @NickTransmissions.

Screenshot_20240917_153741_Torque.jpg

All help appreciated.

Edit to add Tech 2 screenshots..

From the Engine PCM

Screenshot_20240917_161327_Gallery.jpg

Screenshot_20240917_161334_Gallery.jpg

Screenshot_20240917_161341_Gallery.jpg

From TCM



Screenshot_20240917_161137_Gallery.jpg
 
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dkad260

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I cleared all the codes and it goes into gear fine now, haven't driven yet as I want to hear what some say first.
 

j91z28d1

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there was a tsb about the big plug where the harness goes into the tranny rubbing on a heat shelf and wires being damaged. I don't remember the year, but if you can easily get under it. might be worth a check. back passenger side of the tranny I believe?
 
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dkad260

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there was a tsb about the big plug where the harness goes into the tranny rubbing on a heat shelf and wires being damaged. I don't remember the year, but if you can easily get under it. might be worth a check. back passenger side of the tranny I believe?
I tool a look, and the wire loom is away from the shield. Bad angle on the pic but the loom is not touching the metal.


Screenshot_20240917_190654_Gallery.jpg

I also saw the thread by @Apach 031 regarding the ground and will look at that also.

I want to mention, I also had my OBD adapter plugged in when this happened.

Had this for a few years, no problems before.

Screenshot_20240917_191306_Gallery.jpg
 

j91z28d1

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well it did seem like it was a canbus issue.

I honestly don't know. Communication stuff is the worst. unless you can make it fail long enough to trouble shoot it in real time. it's just all guessing
 

mikez71

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e-brake area is another spot to check wiring for wear I believe..
 

NickTransmissions

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This is most certainly an electrical, electronic / communication problem in the CAN-BUS system and/or one or more modules as opposed to a transmission-specific issue...I'd check fuses, wiring, grounds, etc...Admittedly, once the scope of the problem goes outside of the transmission itself, I'm a lot less knowledgeable compared to the numerous other regularly contributing SMEs on the forum.
 
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dkad260

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Thanks for the replies, after reading a few threads I want to add in a timeline that may help. Things about fuel pressure/ fuel pump, wire harness etc have perked my interest So before a few days ago in which I replaced the intake gasket and installed serviced injectors, I was noticing higher LTFT on bank 1 when at idle, about 4-5% higher, but as soon as you touch the gas it evens out, even when driving they were somewhat even, within 1%. This led me to believe it may have an intake gasket leak so I decided to replace the intake gaskets and while the intake was out, to also have the injectors serviced as I was seeing a slight drop in MPG at highway cruise..maybe 1-2 MPG. The injectors are another story as most of the baskets were coming apart and 2 were split. Flow was down 15-20% AND #8 was the odd man out, trailing the rest in flow by another few %. Now all 8 are within .4% and picked up almost 20% flow. After it was back together, the LTFT are very close but idle is about 1-1.5% higher sometimes, not 5%. So far so good for now.

This is where I feel the details matter most and may or may not be the cause of the new codes...When I started the service, I gently tied the wire harness out of the way using a bungee cord, not a tight pull, just high enough to be out of the way, secured to the LH hood hinge, maybe this upset a corroded wire. Next, after all was back together I took it for a few trips and it drove smooth, still learning block values so jury is out. The next day I went to work, no issues, left work and stopped for fuel before the grocery store. Upon leaving the gas station, I noticed a rougher idle and the fuel trims were wacky no CEL, but the MPG on the DIC was normal.

This was my fuel trim at idle after the intake and injector service, and before it was runing rough, still learning block values but maybe 5 drive cycles so far.

idle 1.jpg






When it started running rough this was the screenshot:

driving 1.jpg

The LTFT has never been that far from 0, and during the new drive cycles, maybe 0-4% (both the same) on the LTFT at cruise. Once I shut it off at the grocery store, I came back and it was normal, so I drove home. When I remote started it 8 hours later, that's when it immediately shut off and I had al the codes....but fuel trims were ok.

So my question is, how is the fuel pump connected to the transmission circuit, and/or do they share a common ground? I would think this is not a fuel pump issue and I would think if the pressure was down at that time it would have a higher + trim.

Other than that rough running anomaly, the O2 sensors have been spot on, downstream is a solid line around .7 and the upstreams have a rapid refresh during cruise, as well as fuel trims looking great.
 

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