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Old 03-03-2019, 02:35 PM   #1 (permalink)
Ted White
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2014 Denali will not key off

A search of this forum didn't turn up anything that would help, so here's the problem:

I'm in Mexico and received a call from a guy nearby who owns a 2014 Denali Duramax that has been sitting for a year unused.

He had to put new batteries in it to get it started, but he told me that keying off and removing the key would not stop the engine running.

He contacted me because I am known as the go-to person for sulfur in fuel problems in Mexico and he had nowhere else to turn.

On arrival I found the truck engine running, and sure enough, it would not turn off. It just keeps on running as if the key is still in place, and you can put it in gear and drive it. So I pulled the ECM relay from the main fuse panel to kill the engine.

I did notice that the key fob buttons will not lock and unlock the truck, so I suspect a failed battery in the key fob. Unfortunately the guy does not know where his second key is, so there's no alternative to the one available key.

Has anyone experienced this issue or knows the exact cause?

Thanks

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Old 03-03-2019, 03:02 PM   #2 (permalink)
TheBac
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Sure its not a BCM issue?

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Old 03-03-2019, 03:09 PM   #3 (permalink)
Ted White
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Unfortunately there's no way for me to test a Body Control Module in Mexico, and dealerships here do not service diesels, so going to a dealership would be a waste of time. That's why I'm hoping someone else has actually EXPERIENCED THE ISSUE and can explain what happened in that case. It would be a starting point to see if we can do something down here.
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Old 03-03-2019, 07:25 PM   #4 (permalink)
redwngr
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Should be able to get a fob battery at a department store.
Pretty sure it will be the CR2032 or equivalent battery. They are only a couple of dollars.

IMO it won't fix the problem, but you'd know for sure.

To replace the battery:
1. Separate and remove the back cover of the transmitter with a flat, thin object, such as a coin.
2. Press and slide the battery down toward the pocket of the transmitter in the direction of the key ring. Do not use a metal object.
3. Remove the battery.
4. Insert the new battery, positive side facing up. Replace with a CR2032 or equivalent battery.
5. Push together the transmitter back cover top side first, and then the bottom toward the key ring.

There will be a diagram of this under RKE in the owners manual.


Might also use manual to help track down a possible relay that has contacts welded shut so that power for ecm/fuel injection that isn't getting shut off.
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Old 03-03-2019, 10:22 PM   #5 (permalink)
wq93
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I had this happen with my 2006 Sierra. When I went to start it one day the CEL was on before I put the key in the ignition. The engine started and the truck drove normally but it wouldn't shut off with the key and I had to pull the ECM relay. The problem was intermittent and most days it worked perfectly with no CEL and the ignition shutting off as it should making it difficult to run down the problem. The only DTC set was for loss of communications between the ECM and separate TCM for the Allison.

Fast forward a couple of months. I bought the Helms manual set for the pickup and the next time the problem occurred I was ready to run some tests. I found that when the batteries were disconnected and reconnected, with the ignition off the switched 12 volt bus would slowly increase in voltage and when it reached a critical level the ECM relay would activate turning on the CEL and preventing the engine from being shut off. The CEL was occurring because the ECM was receiving normal voltage through its now activated relay while the TCM was not powered up.

The problem was from a mouse who had urinated on the upper level of the UBEC (where the fuses and relays live). The center layer has open copper bus wiring that interconnects the various circuits between the main connectors on the bottom of the sandwich and the fuses and relays on the top. This is bare copper that runs through an insulating maze/grid. The mouse urine created a corrosion deposit between the switched and constantly powered 12 volt buses and when the humidity was high enough it became sufficiently conductive to "charge" the switched 12 volt bus until the voltage was high enough to activate the ECM relay.

Many of the items on the 12 volt bus will have bypass capacitors and the mouse urine created corrosion formed a resistor with the capacitors forming the other part of a R/C network and the higher the humidity the less time it took to charge those bypass caps sufficiently to create a high enough voltage to activate the ECM relay. It took a couple of hours with the Helms manuals to understand how this part of the system was supposed to work and another 30 minutes with a DMM to narrow the problem. I found a used UBEC from the exact same year/configuration pickup for $40 on ebay and it took maybe 15 minutes to install; typical of this kind of oddball problem where finding the root cause is a pain but once found fixing it was easy.

Both garages have since been equipped with multiple different "mousicide" devices.
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Old 03-04-2019, 09:40 AM   #6 (permalink)
G2GBY
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If you keep the ignition circuit energized, the truck will not shut off.
Does the truck have an alarm, remote start, lift pump?
Maybe something in here
https://www.dieselplace.com/forum/63...-shut-off.html
https://www.dieselplace.com/forum/63...-shut-off.html
https://www.dieselplace.com/forum/63...-shut-off.html

I don to know if it's all lift pumps but all the other diesel sites have problem with air dog raptor. Just seems where it's wired to causes engine to not shut off.
https://www.dieselplace.com/forum/63...-shut-off.html
I don't know how your inner web service is. Google (duramax LMM won't shut off) lots to read

Last edited by G2GBY; 03-04-2019 at 10:06 AM.
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Old 03-04-2019, 10:37 PM   #7 (permalink)
Ted White
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Well, I guess I have to look for mouse pee in the fuse panel, although I didn't notice anything unusual when unplugging the ECM relay. Getting parts down here will be the problem, so I'm even wondering whether to try unhooking the batteries, washing the fuse/relay area, and letting it dry for a couple of days. I'll think about that some more.

Nothing in all the reading from G2GBY seems to apply in this case. There are no fault codes, and the truck has simply been sitting for a year with the batteries slowly dying. No mods or wiring changes. I'm starting to like the idea that it's mouse pee.
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Old 03-04-2019, 10:48 PM   #8 (permalink)
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Ted,

Any time a vehicle is allowed to sit for a long time it really increases the odds of rodent damage. It is worse these days because both soy and peanut oil are widely used in making wire insulation which makes them even more attractive to rodents.

The photos below are of the middle section of the UBEC which lies below the relays and fuses on the top layer. The only signs of damage to the top were a small mark that MAY have been from gnawing on one decal and an obvious stain near one fuse. But once I took it apart the damage was obvious as you can see in the detail photo. After I removed the UBEC but before disassembly I hooked meter leads to the two supposedly separate ignition switched and constant 12 volt buses and as I increased the humidity in the container that held them the resistance started dropping immediately at which point I was confident I had found the problem and taking it apart sealed the deal.

Good luck figuring out the issue with the truck.
Attached Images
File Type: jpg UBEC construction.jpg (58.7 KB, 15 views)
File Type: jpg Damaged area.jpg (474.1 KB, 64 views)
File Type: jpg Resiistance measurement.jpg (326.3 KB, 64 views)
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Old 03-05-2019, 10:18 AM   #9 (permalink)
Ted White
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Well those are certainly interesting photos - thanks for all that excellent detail.

Overnight I've made a decision to step back from giving assistance on this problem. As mentioned, it's in Mexico, and the truck has been sitting for a year with the batteries slowly going flat.

The owner seems to be in alzheimer's - has no idea what is going on, and it is his Mexican wife who is trying to get the truck running, presumably to sell it, but that's not exactly clear.

Anyway, I showed the wife's brother(?) how to stop the engine by pulling the ECM relay, and they seem happy with that solution. It is not at all unusual in Mexico to be using unusual methods to keep vehicles running.

It's unfortunate that this lady is in this position, but it will almost certainly become significantly more complicated for me if I stay on the case.

Thanks for the help on this file.
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Old 03-05-2019, 10:18 AM   #10 (permalink)
Ted White
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Well those are certainly interesting photos - thanks for all that excellent detail.

Overnight I've made a decision to step back from giving assistance on this problem. As mentioned, it's in Mexico, and the truck has been sitting for a year with the batteries slowly going flat.

The owner seems to be in alzheimer's - has no idea what is going on, and it is his Mexican wife who is trying to get the truck running, presumably to sell it, but that's not exactly clear.

Anyway, I showed the wife's brother(?) how to stop the engine by pulling the ECM relay, and they seem happy with that solution. It is not at all unusual in Mexico to be using unusual methods to keep vehicles running.

It's unfortunate that this lady is in this position, but it will almost certainly become significantly more complicated for me if I stay on the case.

Thanks for the help on this file.

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