Need help with damaged wiring harness through firewall

gus4200

Member
Need some help with a damaged wiring harness through firewall, 2007 Trailblazer LS 6 cylinder

Long story short: I was running a power wire for an amp, and somehow damaged a blue wire in the main harness going through the firewall.

From what I can tell, only one of the wires is damaged but it's definitely "cut"

When I start up the Blazer, the 'reduced Power mode' light comes on and i'm getting a message that Stabilitrak is turned off (and I can not turn it back on)

It's throwing code: P2122

So... how expensive of a f*** up was this? to replace that main harness the runs through the firewall?

Also, any idea on the part #

Thanks in advance. God, I'm literally sick to my stomach.
 

MRRSM

Lifetime VIP Supporter
The Blue Wire that got cut apparently carries the direct feed from your Accelerator Pedal (Gas Pedal) to the PCM ...and the Code P2122 is a definitive in describing a Broken Circuit as being one of the causes. In cases where either the ACC Pedal Sensor, The Throttle Position Sensor or the Mass Air Flow Sensor are compromised or interrupted by a Short Circuit in the wiring... The PCM responds by automatically shunting the Engine to a "Reduced Power" Level.

Just an FYI... The ACC Pedal Sensor sends TWO signals to the PCM with different reference Voltage Ranges (One High and One Low) and it figures out the variance between the two in order to know how to set the responses. When married with the other Inputs from the O2 Sensors, the Throttle Body Position for Air Intake...and the MAF Sensor as it actually WEIGHS the volume of air passing through it while using the IAT to measure Air Temperature versus Air Density.... the PCM figures out where its Power and Torque Band should be. If either one of the Two Signal Wires from the ACC Pedal gets cut... The PCM protects the Engine via a Reduced Power response.

BEFORE BEGINNING THIS REPAIR...REMOVE THE (-) NEGATIVE GROUND BATTERY CABLE...

The best thing to do is to figure out which side of the Firewall will give you the easiest access...and pull as much of the free harness as possible in that direction without harming any other wire harness wires or their connectors in order to perform a proper sectional wire replacement. Slip some Shrink Insulation Tubing (2 pieces) over each end of these two broken wires FIRST before continuing. When the repair is done... then you can slip the Shrink Tube Insulator back over both repaired ends and use a few Wooden Scratch Matches to heat it up and shrink it tightly around the repaired wires.

Strip the broken wire ends of their Blue Plastic Insulation back about 1/2". Then use a fresh length of Insulated Copper Wire of the same approximate Gauge and use a Soldering Gun with Non-Lead Rosin-Core Electronic Repair Solder to re-attach the two broken ends to the new wires segment and solder them carefully together. Then slide the Shrink Insulation Tubing over the Two Soldered points and shrink them down around these locations. (If you are superstitious... you COULD install the Battery Graund Cable now and try to Start the Engine before proceeding...) Then tightly Re-Wrap the Repair with Black Electric Tape and as carefully as possible ... slip the Harness slowly back into the Firewall Pass-Through and Rubber Grommet. Re-Install the Negative Battery Ground Cable... Have a Seat in the Driver's Side... Take a Deep Breath... Start the Engine... and if it runs Okay... Exhale with Great Satisfaction.
 
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gus4200

Member
Thanks for the reply. I would like to repair but I'm not sure it can be done at this point...

Where it's cut is inside the grommet, and I can't see the other piece of the cut wire going into through the firewall.

If I have to unhook that wire bundle/harness from the main fuse block & PCM anyway, just to be able to get to the cut segment... any guesstimate on what would just a replacement wiring bundle/harness would cost? (and what part #)
 

MRRSM

Lifetime VIP Supporter
Gus... Your 2010 flavor of this Truck Line Series would run you anywhere from $600 to $800 for a Complete New Engine Harness... and since your vehicle is new enough not to suffer from a great deal of insulation brittleness... doing the tedious task of removing whatever needs to be undone to get you enough 'lebensraum' to do the work...will be well worth your efforts. If you have the wherewithal to take those thing apart... I have no doubt at all that you will dope out a path to being able to fix this in short order.

Please remember that you must use a great deal of caution if you are removing components that leave circuitry exposed to the elements of the weather...so take the necessary precautions to cover anything with exposed female connectors using Plastic Baggies and Tape them up snugly to keep out the Rain and Snow while you fix the Busted Wire(s). The key here is ...Slow is Smooth Smooth is FAST...and that way nothing else will get pulled, stretched or broken along the way.
 
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gus4200

Member
I was afraid you were going to say something to the tune of $600 - $800... And I would imagine that's just for the part itself.

I've talked to my Father-in-law about it also... he's got a shop on his property that him & his buddies rebuild cars in... so he said he'll be here tomorrow take a look at it. (Should have taken it there in the first place, but wanted to do it myself... lesson learned)

So we'll definitely be looking at repairing the existing wire(s). My only worry is when we start to dig in and find out I damaged more than the one wire can see. I'm only getting the 1 code thrown, and all other wires look OK. So hopefully it's just one.

But... I'll gladly fix 18 wires if we have to, before shelling out that much for a replacement harness.

Thanks again for your help!
 
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gus4200

Member
Just an update... Dad-in-law & a buddy of his came by today, to help me cut the grommet to get to the damaged wire (I wasn't very comfortable doing it as I didn't want to further damage any more wiring at this point)

Cut the grommet, had to solder 2 wires (there was another wire I damaged than the one I could see), got everything back together & NO CODES being thrown & BACK IN BUSINESS. Rewrap & glue (silicone) the grommet boot & gonna let the Blazer sit for 24 hours while the silicone cures.... so far so good!

Thanks again for your help, MR. RSM!

Now... onto getting the driver's window switch panel replaced (which I'm trying to get with the dealer about for the recall)...

and replacing the fuel sending module (fuel gauge stopped working --which I've read the 07's are notorious for having problems with)
 

Alec20

New Member
Hi gus4200.
I have the same exact issue but on my 06 Silverado and mine is an orange wire I severed. How were you able to get that grommet back together? Is there a way to free that whole wiring harness?
I am putting in a car stereo and am having trouble getting my head unit to turn on after install. Anyone know what this orange wire could go to? Want to know if that has something to do with the head unit...
Thanks, appreciate any help in advance!
 

MRRSM

Lifetime VIP Supporter
Welcome to GMT Nation...

As a Brand New Member... you are about to discover what an advantage this really is when you visit THIS Link and can Download a FREE GM OEM Full Size Factory Truck Service Manual. These Zipped PDFs (Courtesy the work of @Mooseman) contains the Wiring and Electrical Connector Diagrams you will need for tracing out any connection issues and showing the Layout of the OEM Radio and Class 2 Network connections required to make things work:

 
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xavierny25

Well-Known Member
I would really like to know why ppl would even think it's a good idea to run more wiring through that boot. Why not let it serve its purpose and just drill and grommet your own hole. There's a whole area to the right of the brake booster with ample space for a drill from inside or out side these trucks. 20200606_113800.jpg

@Alec20 not sure if you have the manual for the current headunit but the orange from most aftermarket headunit is usually the illumination wire depending on what brand it is. What adapter harness are you using and is your truck bose or non-bose system would be my next question to you.
 

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