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.

 

[DJ BigDog]

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

I had been getting the P0455 evap trouble code for awhile and the tighten fuel cap message so I finally replaced the Evap Solenoid Sensor and cleared the codes and that seemed to fix my issues.

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

Turned out to be a bad ground cable on back side of engine to firewall. Also took out the TPS actuator solenoid. Check all grounds everywhere! And the wire harness and connector at the throttle body.

 

[Alberta Tahoe]

Thanks for that. I'll have to get into this on a whole other level as the condition has become worse.
The intermittent connection now appears to be permanent. After being away for two weeks and the truck parked, attempting to start it resulted in nothing. As if the battery was disconnected. Then the gauge function returned (with no fiddling on my part) although all indicators were at zero. Further to that, removing the key made no change whatsoever. The data centre was still active and the dash idiot lights remained on despite the key being pulled from the ignition switch.
To me , this points to the ignition switch as being the culprit but short of doing a re and re, I have no way to determine if that's the case.

 

[Alberta Tahoe]

(Copied from my other related threads)
Thinking this over and considering the real value of the vehicle to me (both in what it's worth and what it would cost to replace) I'm of the mind that buying a 2nd one that's still running may be the way to go. I've found a 2003 model and a 2001 for under $1500 either of which might be a suitable donor. At the very least I can say that they don't have the same issue mine does (in that they're driveable) and I'd have a pile of parts to swap in an attempt to isolate the problem. My thinking is that a dealer could possibly cost double that amount and still not remedy the situation.
This '06 was purchased for $5000 a little over two years ago and besides new shocks, front shock bushings and tires, it's required nothing other than oil changes and an air filter.
Still thinking...

 

[Alberta Tahoe]

(Copied from my other related threads)
http://www.tahoeyukonforum.com/threads/electrical-issue-is-expanding.93566/

http://www.tahoeyukonforum.com/threads/body-control-module.93759/

Thinking this over and considering the real value of the vehicle to me (both in what it's worth and what it would cost to replace) I'm of the mind that buying a 2nd one that's still running may be the way to go. I've found a 2003 model and a 2001 for under $1500 either of which might be a suitable donor. At the very least I can say that they don't have the same issue mine does (in that they're driveable) and I'd have a pile of parts to swap in an attempt to isolate the problem. My thinking is that a dealer could possibly cost double that amount and still not remedy the situation.
This '06 was purchased for $5000 a little over two years ago and besides new shocks, front shock bushings and tires, it's required nothing other than oil changes and an air filter.
Still thinking...

 

[afpj]

I apologize if you've done the following suggestion already, as following this is somewhat difficult spread across 3 threads.....

With battery disconnected, have you disconnected and cleaned (like with electrical contact cleaner) the bus connectors to the bcm and Pcm? Have you tried a different battery? It's almost as if you have loose plates in the battery and they short out going over bumps. Just trying to throw out 'cheap' suggestions.

 

[Alberta Tahoe]

Yes. I've spread the subject across a few threads although each one was addressing something somewhat different. I've found it to be an effective way to solicit additional responses as threads tend to go stale.
To answer your questions, (one of which you asked in another thread regarding the battery and I answered): Two batteries. Both test OK (although not loaded tested but that's not relevant here). I had thought about the battery being defective too. No difference.
You do bring up a good point regarding the connections at the PCM. It may have been mentioned before too. That is something I had on my list of "to try" but sort of had given up. I've renewed interest now that I've been away for a couple of weeks and I'll address that when I'm back under the hood. The BCM too although if you could see the dust and dirt under the hood (not to mention the moisture that must accumulate), the PCM is the more likely target.
It'll be another couple of weeks before I'm back at it.

 

[ill_noiz]

I would try installing new wire for all the electrical connections from the battery/alt. Something similar to doing the big 4 upgrade.

 

[Alberta Tahoe]

I'm not familiar with the big 4 upgrade.

 

[Alberta Tahoe]

The truck has been parked since the post above until recently. (3 years plus the one year since I started on the repair) Having my other Tahoe stolen (that's another story) forced me into fixing this one.
What happened up to this point and my attempts at repair compounded the situation and made diagnosis all but impossible with the limited experience I have on these vehicles (and I'm an old school auto technician and currently a master electrician).
So I had it towed to an independent one man shop which I became acquainted with when getting into this originally.
Ultimately the main issue was traced to the throttle body wiring harness. More specifically, to the ground wire in that harness that connected to the passenger side cylinder head.
I had complicated matters by: removing and re-installing the (same) PCM, replacing the electrical side of the ignition switch and as it turns out trying to do my troubleshooting (via a Tech 2) with a faulty (truck) battery.
Interestingly, it was this battery that led to the original no start condition that arose after having been parked for two weeks. The intermittent electrical was already an issue prior to this. The battery in question showed proper voltage. It also load tested well. It was off and on various chargers (smart and otherwise). What the battery was doing was performing as it normally would then for whatever reason, (perhaps via an internal short) would sort of half drop out. When this happened, the instrument cluster would not fully shut down, the door locks became inoperable and the ignition switch lost most of it's functionality. There were probably other issues as well but the gauges not shutting down entirely would ultimately drain the battery over a day. I never got to the point of starting from square one again as another truck purchase put this on the back burner. It was my mechanic who related this same story to me and it fit perfectly with what I had experienced in my testing. Various batteries had been in and out but as it happened, the faulty battery was in the truck when it arrived at the shop.
Anyway, to sum it up, the original intermittent electrical was traced to a poor ground and the inability to diagnose this (as the Tech 2 kept losing communication) was traced to the battery.
The truck is now back in service.