Multiple codes, ground issues, ECM, BCM, SOLVED!

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Apach 031

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Hey everyone. 2008 Yukon Denali, 6.2 AWD. I have seen a ton of posts on this topic, but rarely have seen anyone post a follow up with the resolution. So here is what worked for me.

The issue I was having is as follows: after startup, vehicle would run fine for between 5 and 10 minutes. Once the temp gauge was up to normal, within about 2 minutes, the door chime would start ringing repeatedly, the check engine light would come on, stabilitrak would turn off, service suspension message would turn on, the speedo and tach would jump around like crazy, and the vehicle would lock into 2nd gear (limp home mode I think?). This went on for several months, initially at random times, and eventually, everytime I used it. Multiple codes would show, and the truck would stay in limp home until it cooled down, AND I cleared the codes. They were somewhat random which codes would show, but the 2 consistent ones were P0700, and U0073.

Checked everything I could, under the assumption it was a ground issue. Did the big 3 upgrade. Battery was a little weak, so I replaced it. Unplugged every control module, cleaned connection, and re-installed. Cleaned and re-installed the ground under the drivers seat.

What finally worked was a combination of 2 things. I did them both at the same time, so I can't be sure which was the magic bullet. First, the wiring harness that goes into the tail of the transmission. It leaves the transmission, and immediately loops up, and goes overtop of it. The Y pipe for the exhaust is directly beside it, and there is a heat shield bolted to the side of the transmission. In my case, the wire loom was laying against the heat sheat, and about 4 inches of it had melted away, leaving the wires against the shield. I couldn't see anyplace where the wire insulation had melted through, but I wrapped them all in black tape, put a new piece of wire loom on, and snap tied to the side of the trans so they could no longer touch the heat shield. In my mind, this was the solution.

The other thing I did was, I unplugged my pioneer stereo from the OBD port. My stereo has a built in code reader. It has been plugged into the port for about 2 years, but I have seen other people have issues with cheap OBD scanners messing with the ECM, so I unplugged it for good measure.

Been 2 weeks of daily driving, no repeat of the issues so far.

Happy driving.
 

Geotrash

Dave
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Hey everyone. 2008 Yukon Denali, 6.2 AWD. I have seen a ton of posts on this topic, but rarely have seen anyone post a follow up with the resolution. So here is what worked for me.

The issue I was having is as follows: after startup, vehicle would run fine for between 5 and 10 minutes. Once the temp gauge was up to normal, within about 2 minutes, the door chime would start ringing repeatedly, the check engine light would come on, stabilitrak would turn off, service suspension message would turn on, the speedo and tach would jump around like crazy, and the vehicle would lock into 2nd gear (limp home mode I think?). This went on for several months, initially at random times, and eventually, everytime I used it. Multiple codes would show, and the truck would stay in limp home until it cooled down, AND I cleared the codes. They were somewhat random which codes would show, but the 2 consistent ones were P0700, and U0073.

Checked everything I could, under the assumption it was a ground issue. Did the big 3 upgrade. Battery was a little weak, so I replaced it. Unplugged every control module, cleaned connection, and re-installed. Cleaned and re-installed the ground under the drivers seat.

What finally worked was a combination of 2 things. I did them both at the same time, so I can't be sure which was the magic bullet. First, the wiring harness that goes into the tail of the transmission. It leaves the transmission, and immediately loops up, and goes overtop of it. The Y pipe for the exhaust is directly beside it, and there is a heat shield bolted to the side of the transmission. In my case, the wire loom was laying against the heat sheat, and about 4 inches of it had melted away, leaving the wires against the shield. I couldn't see anyplace where the wire insulation had melted through, but I wrapped them all in black tape, put a new piece of wire loom on, and snap tied to the side of the trans so they could no longer touch the heat shield. In my mind, this was the solution.

The other thing I did was, I unplugged my pioneer stereo from the OBD port. My stereo has a built in code reader. It has been plugged into the port for about 2 years, but I have seen other people have issues with cheap OBD scanners messing with the ECM, so I unplugged it for good measure.

Been 2 weeks of daily driving, no repeat of the issues so far.

Happy driving.
Heck yeah! Nice work on the troubleshooting and thanks for following up with what worked!
 

bobby2175

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Hey everyone. 2008 Yukon Denali, 6.2 AWD. I have seen a ton of posts on this topic, but rarely have seen anyone post a follow up with the resolution. So here is what worked for me.

The issue I was having is as follows: after startup, vehicle would run fine for between 5 and 10 minutes. Once the temp gauge was up to normal, within about 2 minutes, the door chime would start ringing repeatedly, the check engine light would come on, stabilitrak would turn off, service suspension message would turn on, the speedo and tach would jump around like crazy, and the vehicle would lock into 2nd gear (limp home mode I think?). This went on for several months, initially at random times, and eventually, everytime I used it. Multiple codes would show, and the truck would stay in limp home until it cooled down, AND I cleared the codes. They were somewhat random which codes would show, but the 2 consistent ones were P0700, and U0073.

Checked everything I could, under the assumption it was a ground issue. Did the big 3 upgrade. Battery was a little weak, so I replaced it. Unplugged every control module, cleaned connection, and re-installed. Cleaned and re-installed the ground under the drivers seat.

What finally worked was a combination of 2 things. I did them both at the same time, so I can't be sure which was the magic bullet. First, the wiring harness that goes into the tail of the transmission. It leaves the transmission, and immediately loops up, and goes overtop of it. The Y pipe for the exhaust is directly beside it, and there is a heat shield bolted to the side of the transmission. In my case, the wire loom was laying against the heat sheat, and about 4 inches of it had melted away, leaving the wires against the shield. I couldn't see anyplace where the wire insulation had melted through, but I wrapped them all in black tape, put a new piece of wire loom on, and snap tied to the side of the trans so they could no longer touch the heat shield. In my mind, this was the solution.

The other thing I did was, I unplugged my pioneer stereo from the OBD port. My stereo has a built in code reader. It has been plugged into the port for about 2 years, but I have seen other people have issues with cheap OBD scanners messing with the ECM, so I unplugged it for good measure.

Been 2 weeks of daily driving, no repeat of the issues so far.

Happy driving.
I know this will probably be painful, but I've had this exact same issue for years on my 2010 Yukon XL Denali. $4,000 at the dealership to find the issue....they said it was fixed and it lasted a couple of years and I'm right back there again now. Seems very possible it's the harness at the transmission with the way you describe it. Been slowly getting into some basic vehicle repairs, but haven't gotten to anything like this. Can you point me a little bit on how best to find the harness?
 
OP
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Apach 031

Apach 031

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I know this will probably be painful, but I've had this exact same issue for years on my 2010 Yukon XL Denali. $4,000 at the dealership to find the issue....they said it was fixed and it lasted a couple of years and I'm right back there again now. Seems very possible it's the harness at the transmission with the way you describe it. Been slowly getting into some basic vehicle repairs, but haven't gotten to anything like this. Can you point me a little bit on how best to find the harness?
Sorry for the late reply, Bobby. I'm on vacation right now, so I can't take any photos. But if you are under the rig, it's on the passenger side of the trans. It comes from the driver's side at the front, comes up over top of the transmission, and loops around and facing forwards before entering the transmission. Mine was laying just slightly over onto the exhaust heat shield. Hope it helps. Let me know, I can take some photos when I get home after the 27th.
 
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Apach 031

Apach 031

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Hey folks. A quick update. After about 2 months of trouble free driving, the symptoms returned about 3 weeks ago. This time far worse. The system would go into limp home mode anytime the temperature outside was above around 50 degrees. Resetting the battery didn't help, the symptoms would return immediately.

I finally bit the bullet, bought a subscription to Alldata. Boy was it worth it. Working through the diagnosis steps for a P0073 code, I narrowed it down to a bad ground through the OBD port. Started resistance checking all of the ground cables from there back. Finally found it. The main ground for the ecm, as well as a couple of other modules was almost broken right through. This is the one that bolts to the front passenger side of the engine block, where the main battery ground bolts to as well.

I had already upgraded the battery ground cable, and cleaned this ring terminal up really well. But where the terminal crimps onto the wire had almost broken completely through the wire. I presume because of engine vibration over the years. Note that this was tucked up into the wire loom, and I had handled it a couple of times without seeing it. Had to pull the wire out of the loom to see the problem (actually felt it first).

Cut the wire back 2 inches, a new terminal, and life is good again!
 

Geotrash

Dave
Supporting Member
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Hey folks. A quick update. After about 2 months of trouble free driving, the symptoms returned about 3 weeks ago. This time far worse. The system would go into limp home mode anytime the temperature outside was above around 50 degrees. Resetting the battery didn't help, the symptoms would return immediately.

I finally bit the bullet, bought a subscription to Alldata. Boy was it worth it. Working through the diagnosis steps for a P0073 code, I narrowed it down to a bad ground through the OBD port. Started resistance checking all of the ground cables from there back. Finally found it. The main ground for the ecm, as well as a couple of other modules was almost broken right through. This is the one that bolts to the front passenger side of the engine block, where the main battery ground bolts to as well.

I had already upgraded the battery ground cable, and cleaned this ring terminal up really well. But where the terminal crimps onto the wire had almost broken completely through the wire. I presume because of engine vibration over the years. Note that this was tucked up into the wire loom, and I had handled it a couple of times without seeing it. Had to pull the wire out of the loom to see the problem (actually felt it first).

Cut the wire back 2 inches, a new terminal, and life is good again!
Awesome!! Thank you so much for following up and I'm glad you found what will hopefully be the final smoking gun!
 

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