Hey Scotty,
I have a 2014 Chevy Silverado 1500 LT 5.3L V8. Recently I've had a transmission issue, which can not be diagnosed until... this electrical nightmare is solved. The electircal issue presented a month after I had the truck towed back to my house. I noticed that the interior of the cab had exessive moisture with condensation presenting on the interior of the windows. Went to start the vehicle, battery was dead. There was/is some type of parasitic draw. Once I jumped the battery, instantly the horn began to blare, not beep, but blare continuosly. The front and back turn signals circuits are open, the cab lights are all on, the door locks do not work, the highbeams are on. No switches are on inside the vehicle. When the key is turned to the accesory position, the wipers begin at full speed and the fluid is on. I yanked all the fuses for the wipers, fluid, and horn to diagnose the issue. I noticed the cowl at the base of the windshiel was warperd which most likely led to the moisture issue, so I replaced it. I cleaned all interior and exterior connectors pins, replaced the junction fuse box under the hood and the distribution block on top of the battery to no avail. Changed the battery thinking it was a low voltage issue due to the code B1517-5A being present... no fix.. The codes I'm pulling from my OBD2 are contradictory as well, saying the components that are stuck on have shorted to ground, but are also open, which led me to think that the battery distribution block was faulty.
For example: B3875-02 and B3875-04 are presenting on the same read.
The radio, climate controls, and windows all work... it also cranks and runs so it's not the theft deterrent system, or it could be the theft deterent system trying to turn on, but if it's an issue with the BCM being shot... well you get the idea.
My dilema is that in order to the trans diagnosed, the garages tell me I need to fix the electrical issue first. Which is pretty costly as I have to tow the damn thing everywhere, because I do not trust the transmission to get me to where I need to go.
What tests would you recommend to locate the draw, which killed the battery to begin with, and to locate any shorts in the vehicle?
I've inspected for rodent activity, however I've found none and the wiring harnessess all look to be in tact.
I'm at a bit of a loss here... hope you can help.
Most of that stuff, wipers, high beams, horn, turn signals, child security lock relay control, are on the X5 connector of the BCM.
Door lock controls are on the X6 connector.
Interior light control is on the X7 connector.
Sounds like it's time to inspect the BCM and its connectors
Hey Jack, thanks for your reply. I checked all the connectors and cleaned them with the proper electrical cleaner. I didn't observe any corrossion or splitting of the casings, but I cleaned them anyway. Still no luck
When you have all kinds of electrical problems at once it can be overwhelming
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It's best to pick the easiest circuit and troubleshoot that one
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In your case, the horn circuit
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So, using the diagram you can figure out if there's a Ground being provided to the X4 connector, pin G1 on the underhood fuse box
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If not and the horn is blowing it's a problem in the underhood fuse box
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If there is a Ground there, is it coming from the BCM or the horn switch?
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If it isn't coming from the horn switch then check to see if it's coming from connector X5, Pin 18 on the BCM. If so, that narrows it down to the BCM
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The X5 Pin 19* for the horn is reading between 1.10V and 0.8V. My fuse box ticks, the same as if the 4 ways are on, that metronome, when I disconnect the X5, it stops clicking, and the headlights and 4 ways turn off. The dash cluster however still shows the highbeam indicator and 4 way indicator as on.
The mystery deepens
By the way, for obvious reasons, I've pulled the horn fuse to shut the darn thing up. Should I repeat the reading with a set of ear plugs and a text to the neighbors?
The diagram shows X5 pin 18, not pin 19. You should not have continuity to Ground on X5 pin 18 when you back probe the wire at the connector
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You can do the test with the horn fuse removed
I mean no disrespect, but are you sure that diagram is correct? When sourcing the pin connector views from GM's electronic manual for the 2014 Silverado 1500 LT 5.3L V8, it shows Pin 18 on X5 as this - 18 - 0.35 - BN/VT - 1969 - Headlamp High Beam Relay Control. With Pin 19 being the Horn Relay Control.
You can't disrespect me when it comes to discussing automotive electrical circuits unless you drag the women in my family into it
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No, I'm not sure. I'm using free diagrams I pulled up on the internet. Is the headlight high beam relay control also "Ground Side" controlled by the BCM? It probably is
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If that's the High Beam control pin, and the High Beams stay on, the same thing applies. Your high beam pin on the X5 connector should not have continuity to ground when the high beams aren't turned on
Haha well I'll be sure to leave them out of this! I'm thinking the issue is with the BCM. I ran a short finder all over the engine harnesses and dashboard wiring and so forth. Couldnt find any shorts at all, I think it's the BCM. I did run a test for faults and one of them was Unreadable Data From BCM. So since the engine cranks over just fine, it's not the PCM, even though I'm getting a reading that the PCM Shorted.... I think the BCM has just decided that hey, with your transmission issue, I think I'm going to join it and piss you off further.
Tested the battery while running, 14.8v was it's average. Ran a whole system diagnostic.
All BCM codes are below.
B3140-00
B3948-02
B3875-02
B1517-5A
B256B-00
B2750-02
B252C-00
B3145-00
B2740-00
B3948-04
B3150-00
B3875-04
B3873-01
B101F-F0
B873-04
B3006-02
B3951-04
B3806-00
B3155-00
B2750-04
B3950-04
B3951-02
B2530-04
B2745-02
After wiping the codes and rerunning I am left with
B101D-F0
B3145-00
B3806-00
B3140-00
B3006-02
B1517-5A
B3150-00
B3155-00
B3875-02
B3948-04
B256B-00
B3949-04
B2745-02
B2740-00
B3875-04
B252C-00
I've been looking into this so I went to the GM Upfitter site for 2014 light duty full size C/K trucks, and dammit, I screwed up with that wiring diagram and BCM pinouts I posted.
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Sorry. That was sloppy research on my part and Scotty will probably reduce me by 2 ranks and put me on bread and water for 30 days
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They confirm your Horn BCM pinout on BCM X5 pin 19
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I have 2 questions. Since you mentioned moisture and condensation, what's going on with the X3 BCM connector?
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Using an incandescent test light with the alligator clip clipped to battery voltage, if you disconnect the X3 connector and touch the test light's probe to the X3 pin 18 wiring connector does the test light light up?
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It shouldn't without the horn being pressed. There's several inputs on that connector and that may be a clue to a problem in that harness
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Secondly, again, if you back probe the X5 pin 19 connector (connector connected to the BCM) and do the same thing with the test light does the test light light up?
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It shouldn't unless the transistor is somehow being switched on by the BCM which would point to an internal fault in the BCM
It's all good! Scotty if you're reading, cut him some slack would ya? =)
So here are the findings.
Resting Battery Voltage - 12.3v
x# - X Connector
/# - Pin
x3/All - 0.00v
x4/20 - 12.3v
x5/3 - 12.3v
x5/4 - 12.3v
x5/19 - 10.3v
x5/18 - 10.3v
x5/17 - 10.3v
x5/23 - 10.3v
x5/22 - 11.3v
My apologies, if there is voltage listed next to the x#/# formula, that means yes it lit up. I have an LED Test light that shows voltage.
Am I correct in assuming that you have the alligator clip on your test light clipped to a good ground and you have both of these BCM wiring connectors DISCONNECTED and you're testing the voltage at the disconnected wiring connectors by probing their pin sockets with your test light?
Yes, you are correct.
Locating parasitic draw is usually pretty straightforward, as in the video below. You'll also want to check your grounds since a bad ground can cause all kinds of electrical mayhem.
https://www.youtube.com/watch?v=lRcj1fQcWwU
Well, the only issue with performing this test, is there is no way to turn the highbeams, all turn signals, or cab lights off, other than yanking the fuses.