Rampant Electrical Gremlins - Need Harnesses?

[Kwing]

I figured I'd see if any of you have similar issues with the wiring harnesses and maybe solutions or sources to make them go away.

I have an 07 Tahoe LT with about 230k on the clock. I replaced the engine about a year ago due to DOD issues. I figured at 200k it was easier to just do the whole long block. A week later the check engine light came on saying low voltage on left bank knock sensor. I replaced the sensor, still there. I replaced the sensor with a dealership part, still there. I replaced the pig tail, still there. It could be the ECU from what I've seen, but I'm suspecting the harness because....

My doors are wonky as crap. Drivers side front door is the worst. Go to roll the window down and nothing. Sometimes hitting the lock/unlock button will bring it back to life, sometimes that doesn't respond and i have to open and close the door to bring it back. More and more frequently when i open the door after shutting the engine off the radio stays on and the lights stay off. The lock works about 50% of the time, and the 50% it does work it locks fine, but only unlocks about half way.

Also more frequently I'll be driving down the road and the drivers side front door open warning goes off... randomly. About two weeks ago, the drivers side rear open warning started randomly going off.

The passenger front door has the same issue with the window, but only about once every 2 weeks. That one you have to open and slam the door shut 3 or 4 times to bring it back to life.

They way it's acting, i'm thinking the wiring harnesses are crap. But when i inspect them i can't find any gunk or corrosion on the connectors, no nasty, dry, or burnt wiring. I can wiggle the crap out of all the wires and never replicate the problems.

I have searched everywhere and cannot find new harnesses. I have no clue where to start making new ones. And i'm hesitant as hell to even go down that road since i can't replicate the problem or find any obvious wiring issues. I hate diving into major repair work without even knowing the root cause of the issues.

Thoughts? Suggestions? Sources for harnesses? Alternative diagnosis? I'll take whatever you got.

It's driving me crazy and my wife is ready to scrap the whole truck over it. I like this truck too much to give up on it....... yet...

 

[swathdiver]

Kevin, if you want to solve this problem quickly and the least expensive way, get yourself a Tech-2 or other bi-directional scan tool. You need to be able to test things without the switches and see the internal trouble codes. A subscription to the shop manual at AllDataDIY and buying a pdf copy from SeriousCTBuyer on Ebay will work in conjunction with the Tech-2 on the troubleshooting guides. My guess is that the BCM needs replacing. Maybe the ECM too but you'll spend a whole lot less time and money chasing this down with the Tech-2.

 

[Fless]

I would start with finding, inspecting, and cleaning every ground, possibly upgrading them as I go. And a careful inspection of the battery cables; these tend to corrode from the inside out, not necessarily indicated by a visual inspection.

 

[kbuskill]

I'm with Steve ^^^ on this... replace battery cables and clean ALL connections including the ones on the 175A **** fuse and at the fuse box.

Now is a great time to do the Big 3 upgrade.

 

[Kwing]

So help me understand 2 things:

1. How would the negative battery cable affect only certain systems at any given time?

2. What are the "big 3"?

 

[kbuskill]

So help me understand 2 things:

1. How would the negative battery cable affect only certain systems at any given time?

2. What are the "big 3"?

1. It's not just the negative cable, it's the positive too... this is pretty well documented on this forum. There are so many "computers" in these trucks... ECM, TCM, BCM, etc., and they get real finicky when the power supply isn't stable.

2. The "Big 3" is a term used in the car audio industry to describe upgrading the...
1. Alternator to positive battery terminal.
2. Positive battery terminal to fuse box.
3. Battery ground to chassis/engine.

I upgraded my '08 Burb to 2/0 marine grade tinned copper shielded wire and soldered on my own lugs and used marine grade self adhesive heat shrink.



You can see that the 2/0 wire barely fits inside the ground wire amperage sensor.

 

[Kwing]

I would still think battery cable issues would manifest in other systems, BUT I'll still go through and do some clean up. It's good practice if nothing else.

The only reason i scratch my head a little is because I've had similar issues on two different BMW 540i's I've owned, but in both cases there were multiple systems that went south and got glitchy.

Right now it's mostly the BCM (assuming that's the cause for the sake of argument). The knock sensor issue is in no way intermittent though, so whatever is going on there would be unrelated i would think. It's always the same bank and it's always low voltage.

So I'll dig into the terminals/cables, but certainly keep suggestions coming. The more I can do with each session the better. Time is commodity i don't have an abundance of these days

 

[Doubeleive]

Battery and battery cables and grounds are a good place to start it's very common on GM vehicles, goofy voltage can do all kinds of weird stuff and it's not just one system it can affect anything electrical, these truck's use a high speed lan (serial bus) so one wire can affect various parts if that voltage is low no telling what it may do.

 

[Doubeleive]

another thing to check if you suspect the harness is to look at the harness (inspect it) thoroughly, look for any parts that may be rubbing or wearing on anything, cracked wires, exposed wires, etc. sometimes guys find a spot that has been wearing and some of the wires are broken. just eyeball it all over.

 

[Kwing]

Figured I'd post an update on this in case anyone is similarly struggling. It turned out it was, in fact, the ECU going out... at least for the knock sensor issue. $800 because I had to have a shop do it (guess you have to have a special reflashing tool?), but that problem has been no more ever since.

Still got all kinds of BCM issues, BUT I actually think I've narrowed that down to the stupidest thing I could think of. The driver's side window switch panel. If I tear it apart and clean up the board-to-board connector contacts all my gremlins go away for about 1-1.5 weeks. That ain't just a switch panel, it's a little mini computer. I haven't been able to justify the $200 for a replacement yet, but I'm confident that's the source of the body gremlins now.