Intense Electrical Issue

[Alberta Tahoe]

Here's one for you:
While driving, passing over rough roads (as in a pot hole or rutted gravel roads) will result in the truck experiencing what seems to be a complete electrical failure. It's instantaneous in that, the door locks will change position, the information centre will reset some data, the gauges drop to zero, the cruise control will kick off (and not re-engage until the brake pedal has been depressed) however all functions return after that instant. (other than the cruise). The engine remains running although I can't say if shuts off briefly and restarts itself as it still has RPM.
In extreme cases, the information centre will display "reduced engine power" until I turn off the ignition and wait a few seconds (or a couple of minutes depending).
While I'll be doing a complete examination of the wiring harness', I'm asking if anyone has pinpointed this particular phenomenon? It's as if all battery power is removed for that fraction of a second and is restored before the engine has a chance to shut off and remain off.
Thanks in advance.

 

[HiHoeSilver]

Do some searching here on the forum. You are not the first with this issue. There are a few threads on the subject. Check/redo battery connections and all grounds.

 

[Alberta Tahoe]

I had done a search here (and on the web in general) a few months back but couldn't find anything that matched what I've described. This is why I've posed the question here.
My hope is a shortcut to the solution.
That said, your advice regarding checking the battery connections and grounds is on my list of things to do.
I may at some point need a map of the grounding points as my experience has shown that there are many and in various locations.
In the meantime, I'll rely on a visual examination and forgo the drawings for now.

 

[HiHoeSilver]

I think @DJ BigDog was the last. Maybe he found something and can chime in?

 

[HiHoeSilver]

Here's another thread, I think the same truck.

http://www.tahoeyukonforum.com/threads/heres-a-weird-one.89340/

 

[rockola1971]

after you check/clean/tighten the battery connections take a look at the ground behind the engine down on the firewall. They are notorious for getting corroded to the point that the connection physically breaks.

 

[Alberta Tahoe]

These replies gentlemen are precisely why I ask these questions.
This thread in particular (which escaped my searching abilities)...
http://www.tahoeyukonforum.com/threads/heres-a-weird-one.89340/
...describes exactly my scenario (thanks HiHoe).
What is lacks however is which ground was the culprit and as you know, there are many.
I've checked the obvious: battery terminals, ECM connections, the main battery to engine block lug and all were not suspicious.
However, that said, rockola's reply, referencing the ground on the firewall behind the engine, helps me to target the grounds a little better.
Thanks again for the directions and ideas.
Back to the Tahoe....

 

[rockola1971]

The ground behind the engine on the firewall affects the stuf light dash lights, power locks, etc. All the stuff that passes thru the BCM. The reduced engine power mode could be a number of things. I had it just myself on a 05 Yukon Denali that I picked up in late December. It was the TPS on mine. The wiring harness at the TPS commonly gets broken conductors just before its plug at the TPS. (Insulation will be intact but inside the wires will be broken.) The reduved engine power mode is for safety of the throttle system. If the accelerator position and the Throttle Body position of the butterfly dont agree within a certain small percentage then you get the reduced engine power mode. This is to prevent throttle runaway and lawsuits on the manufacturer when there is a problem in the throttle system.

 

[Alberta Tahoe]

Having gone through the easily accessible connections like the battery, power tap on the positive battery cable, engine block ground (left front of the block near the oil pan rail), there was no change.
The only ground on the rear of the block that I could find was the typical braided strap from the firewall to the top/centre. It appears to be intact although a visual inspection is difficult (via mirror) and actually getting to it, even more so.
What's more is that after a light drive through wash yesterday (no under chassis spray), the problem worsened to the point where the malfunction would occur randomly and without any bumping. Logically that says says that the moisture has worsened the condition. If that's the reality, I can't say.
I curious as to the condition of the body control module connections. I'll have to investigate that. The ignition switch I understand can also be problematic.
As for the reduced engine power condition, that occurs only when the open circuit (for lack of a better description) happens repeatedly. A particularly rough road would activate/deactivate the door locks, et al, several times and then the limp in mode is initiated.
I've been in the electrical trade for several decades with industrial automation being the focal point. I've been troubleshooting PLCs for a good part of that time and the functionalities of the vehicle electronics are not lost on me. But as always, like going to the doctor with a sore knee, once in the doctor's office, the knee is no longer sore....Such is the case when attempting to remedy an electrical malfunction when no conditions are present or can be duplicated.

 

[Alberta Tahoe]

So, among other things, I've added a section of #10 AWG wire from the stud on the firewall to a solid grounding point on the engine block. This would completely replace the OEM strap if that is the problem.
The condition still exists.
That said, it's severity has been reduced to what it once was when it first appeared. That is, seldom occurring and only on reasonably sized bumps on the road. This doesn't eliminate that connection as the problem but is worth noting nonetheless.
This leads me to my next observation.
From the battery negative post the large gauge cable (looks to about a #4) goes directly to the block. There is also a supplementary wire (approximately #6) which runs from the negative battery post and disappears in and around the rad support. I can't see it's point of termination although it obviously, due to it's size, plays a significant role. I have followed this wire to the point where it disappears into the vehicle structure and have given it a reasonable tug. With the improved condition, I now suspect that there could be an issue here. Does anyone have any clues as to where this might land. This "tug test" was at the same time as replacing the firewall to engine block ground strap.
Without a set of vehicle schematics, this is all sort of a crap shoot.