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Class 2 data bus shorted
Posted to Technical Tips Forum on 3/2/2015 23 Replies

This system, and possibly the issues, are likely old news to many of you, but it was my first time getting a broken data bus on a GM. After many classes and forum posts, I was quite excited to dig into it.

The customer complaint was that the dash was inoperative and there were numerous warning lights illuminated. A code scan on a Snap On Modis Ultra and the Tech 2 network test would not communicate with any module.

A DLC schematic 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Schematic shows me that it's a simple, low speed Class 2 data bus.

I plugged in a DLC break out box and scoped pin 2 with KOEO. 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Waveform I know that I should be seeing 7 volts and at least some activity, but this was flat lined at nearly 5 volts.

Luckily GM was nice enough to install a splice pack to make our lives easier on these 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Photo Removing the shorting bar I can easily check each circuit. 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Photo

I cross referenced the wire colors of SP205 with a schematic, and jumped pin D, which goes to the DLC, to the other wires. 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Schematic

I got some activity when jumping pin D to pin M (BCM) 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Waveform The other pins stayed at 0V, except for pin K.

Pin K jumped up to a steady 11V 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Waveform indicating to me that this baby is shorted to power.

Looking back at the diagram, on the top right, it shows three possible modules with three wires terminating at pin K of SP205. Luckily I only had one Orange/ Black wire at Pin K. This lead me to the Generator Battery Control Module. 2006 Chevrolet Silverado 1500 LS, BATT/Charging/Starting Photo Unplugging the module did not change the voltage at the DLC. The Orange/ Black wire at module also showed the same 11V.

Time to find C100 located between the module and DLC 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Photo Conveniently, it's right next to where I already am, underneath the Underhood Fuse box 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Photo

With the large fuse box covers removed, you can easily flip the fuse box up and peek underneath. 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Photo The first photo is a little hard to tell, but there was some very shiny copper smiling at me under there. Here's a closer look with the connector unplugged. 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Photo 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Photo

The Orange/ Black wire has the insulation chewed off and is shorting out next to the Green/ White wire next to it.

Wham, Bam, thank you rodents. I repaired the wiring and all of my modules were happy and talking. 2006 Chevrolet Silverado 1500 LS, ECM/Inputs/Outputs Waveform Coincidentally, I had a Suburban in a few months back with a whole bunch of wires chewed up in the same area. I guess the rodents like that fuse box.

I had so much fun doing this that I just had to document my process to share with my iATN people. Hopefully this might help someone down the line someday.

Morgan from Minnesota

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car Vehicle Data

2006 Chevrolet Silverado 1500 LT 4.8L

Engine4.8 L
Trans4-speed Automatic (Electronic)