2014 Sierra Left Tail light Turn/Brake/Hazard issue

[Lazorith James Vaughn]

Hello all. I'm trying my best to read and fully understand and fully diagnose the one-line schematics for wiring diagrams.
I keep getting told via the diagrams this light is grounded at "G400," which is right in front of the left rear tire near the rail all the wiring runs.
There is no ground here. However, ground "G121" does exist, which is on the opposite location of this rail located behind the front left tire.

ONLY my Left Rear Tail Light is having these issues. Nothing flashes.
I have checked and replaced the control module under the frame due to corrosion it did indeed fail, internally.
I am not, to the best of my knowledge, getting a voltage signal for Left turn Flash there.

I don't know to say it's the BCM of any kind though since the Left Turn, Hazard, and Brake for the Trailer lights DO Work!

**Please do not suggest I tie into the Tail Light Harness for left turn signal. I am 100% against cutting factory wires under any condition, thanks.**

[Hillwood]

The tail lights have their own wire harnesses that plug into the block by the spare tire.
Check all the wires and connectors there.

Sent from my SM-G965U using Tapatalk

[Lazorith James Vaughn]

@HillwoodThanks for responding! I should note that with the Module, I replaced both complete tail light harnesses. Also, EVERYTHING is GM Genuine, Bought from GM!!
The Tail lights, are not GM though. Though, are Brand New, Bought when I bought these parts, ANSO Brand LED models.

With that stated, I KNOW it's not the Anso, because I tested the other working anso (right rear) in it's location. I also tested with a 7444 Bulb. I also tested with my test light. No power appears to be getting to pin 18(?) it seems at the main control harness to the module. Pin 18, according to my schematic, is Rear Left Rear Turn/Brake/Hazard signal. :-|

Edited December 16, 2018 by Lazorith James Vaughn

[Lazorith James Vaughn]

these are the schematics I am using btw... I can't seem to find 2014? 
https://www.gmupfitter.com/files/media/photo/578/Sierra_Silverado_Electrical_Body_Builders_Manual_Service_Manual_2015_en_US.pdf

[Lazorith James Vaughn]

Hoping someone can give me some other ideas. I been trying to hunt this for a couple weeks now...
Some extra history:
 Back in 2014 I tried to help a guy out by Co-Signing for this Truck.
He lifted it (possibly incorrectly) and put a plow on it without my knowledge. 2.5 years in, he stops making payments. Eventually, I take him to court.
On October 1st, of this year, I won the suit. On October 27th, I went to reclaim it with Title and Judges order in hand. I was friggin stupid and asked for a police escort instead of hiring a Repo. (Never trusting the Police to do the right thing EVER again).  The Police intimidated and forced me to allow him an unsupervised hour to strip off anything that he wants. He removed the stereo, spliced some of those wires, some after market lightning, and some other things that I am unaware of because police refused to let me near the truck. I know he took off some other things because there are random wires that aren't factory there. One of them was spliced into the original Left Tail Light Harness, which was so severely corroded, the metal broke off.

There were engine codes. Stabiltrak. Apparently, dude got into a fender bender a year and half ago on the right driver side. Damage to body was minimal, but it destroyed the Wheel Hub, causing stabiltrak to be off (Due to Hub assumbly, I fixed by replacing.. dude must have pocketed insurance money and didn't get it repaired). On top of that, it was throwing a P06DA code for Consistent High Oil Pressure, a p0420 code (I think due to Advanced timing due to high oil pressure), and p0011, Cam Shaft Position sensor Advanced.

So, I'm tearing down the engine, there is a crap ton of sludge, and I determine the reason for the Oil Pump issue is not because of the Oil Pump (Replacing it anyway), but because of a manufacturer defect in conjunction with the original owner either using Conventional Oil or not changing his oil often enough. I determined that the Oil Pressure Solenoid wire became dry-rotter, and cracked, allowing oil into the connector, displacing the connection, causing an open short, which leave the Electronically Controlled Pressure relief valve stuck Closed (High Pressure), which then put a lot of strain on the time chain and guides, causing deep groves into all guides, eventually breaking one, causing the chain to stretch a good amount.

Under neath the dash, there is only one spliced wire that I can tell of so far. I should look up the pin, but I think it's an ignition wire so it could tell the stereo he had when the engine was on. 
He's stripped out the 2 dash speakers, I assume to eliminate the Door Ding sound. and he removed the Passenger Front Window Motor and replaced with Blocks. After repurchasing a new motor assembly, I determined he likely did this because the rubber seal was getting dry, likely due to dirt, and making the window get stuck rolling half way up. So, I cleaned them then used Wd-40 Silicon based spray and it now functions properly.

There has been water in this truck. I found some standing water under the trim and under the vinyl floor matt.

He HAS sprayed some of the under skirts of the truck with that rubber spray. I am trying to clean it all off.. I definitely had a ground issue at the frame in the rear for the lights/module. I have to super clean and grind that spot to shiny again to renew the connection. Had to do it for G121 too.
For the one in the rear, I determined that one after I noticed the Right tail light would blink but Park Lights would not light up. Though, the Left Tail light would light up.
 

Edited December 17, 2018 by Lazorith James Vaughn
More Info to add

[Lazorith James Vaughn]

waiting on parts

[Lazorith James Vaughn]

Update: I finally determined that Voltage is not being supplied to the Yellow/Blue pin on the K9 BCM

[Lazorith James Vaughn]

Can anyone help me diagnose whether or not the BCM is bad? 
Can anyone help me determine if any of the computer modules are bad?

Remember, Everything works EXCEPT the Left Rear Turn, Brake, and Hazard signals.  and I've just determined that ONLY that Pin (Out of all 4 pins for each light) does not get power.

However, I can't determine where it gets power from. So, I'm having issues testing that pin, since I don't know where it is. I also wish to know how to diagnose circuits.

And to complete.. I found a new Diagram.. and it still says G400 is on that side rail. I am CONVINCED it is not and it's in the rear beside the Control Module >=( But there is no ground fault issue here. and I've cleaned it up nicely.

[Erik Lucatero]

On 12/17/2018 at 1:37 PM, Lazorith James Vaughn said:

Can anyone help me diagnose whether or not the BCM is bad? 
Can anyone help me determine if any of the computer modules are bad?

Remember, Everything works EXCEPT the Left Rear Turn, Brake, and Hazard signals.  and I've just determined that ONLY that Pin (Out of all 4 pins for each light) does not get power.

However, I can't determine where it gets power from. So, I'm having issues testing that pin, since I don't know where it is. I also wish to know how to diagnose circuits.

And to complete.. I found a new Diagram.. and it still says G400 is on that side rail. I am CONVINCED it is not and it's in the rear beside the Control Module >=( But there is no ground fault issue here. and I've cleaned it up nicely.

hey there! i’m having the same issue with my 2014, did you end up fixing it?

[Lazorith Storms]

1 hour ago, Erik Lucatero said:

hey there! i’m having the same issue with my 2014, did you end up fixing it?

 

yes I did!

The issue ended up being a 2 part issue.

 

The ground wire in the rear, P400? Above spare tire was internally broken at its joint. Just repair the entire area there.

 

2. Passenger side fuse panel inside.. there is a 15amp fuse that is blown! It doesn't appear blown, but it is. Remove fuses one by one till you physically find it.

[Erik Lucatero]

so did you end up replacing the tail light junction box, to repair P400 or how’d you repair it? thank you in advance

[Lazorith Storms]

45 minutes ago, Erik Lucatero said:

so did you end up replacing the tail light junction box, to repair P400 or how’d you repair it? thank you in advance

No mine wasn't bad. Juat bad grouns and blown fuse

[Erik Lucatero]

2 hours ago, Lazorith Storms said:

No mine wasn't bad. Juat bad grouns and blown fuse

where is ground P400?thank you

[Lazorith Storms]

17 hours ago, Erik Lucatero said:

where is ground P400?thank you

Right in the back. Slide under, and look around spare tire for a single bolt with .any black wires running to it.

Edited June 10, 2020 by Lazorith Storms

[Vertical]

I had the same left tail light signal problem.  Dealer said BCM..$500. I replaced the BCM @ highway 71 auto @$184...- not fixed. Then I replaced the junction block in the rear - not fixed. I had already replaced left wiring harness. Then Looked for the fuse in the passenger side fuse panel none were bad not there - not fixed. Then checked the left- driver's side FOUND IT. OMG how frustrating. Its # 9 (bcm 7p) on the driver's side 2014 silverado 1500.