[Gmecm] Class2 DIY tools?

[Jay Vessels]

Hi there!

I figure I screwed something up when I changed the heater core.  The BCM 
had to come out, and at one point I removed the IPC, too.  Everything 
worked fine after reassembly for almost a week, then my wife says the 
she lost the fuel gauge, speedometer, and some of the indicators. 
Judging by the Techline CD shop manual, the things I lost were all over 
the Class2 bus, and the things that still work (tachometer, voltmeter, 
oil pressure, SIR indicator) are independent of that bus.  This smells 
like I damaged part of the harness; on this truck, the entire dash 
assembly has to come out, so the odds of a loose ground or pinched wire 
is decent.

It still ran, though, until last night.  I have had the battery 
disconnected and reconnected a few times.  Once while the battery was 
disconnected I disconnected the BCM wiring to make sure I didn't have a 
bent pin, and after reconnecting it and reconnecting the battery, it 
failed to run.  It starts and then immediately dies, as if the Passlock 
code didn't get sent to the PCM.  I'm not sure what I disturbed to break 
that, but I'm wondering if whatever caused the IPC to lose Class2 data 
is now causing the Passlock failure.

I'm calling this Class2 since that is what the Techline CDs are calling 
it.  It's a '99 model truck.  I'm certainly no expert on this.  My day 
job is writing firmware for inkjet printers, not servicing GM cars.

I wonder if I've got a BCM or BCM wiring issue -- I just tried a quickie 
test:  I armed the factory content theft deterrent with the key fob (the 
fob still locks and unlocks the doors) with the window rolled down.  I 
unlocked the door by reaching in and unlocking it manually, then opened 
the door.  Normally that sets the alarm off, but this time it didn't. 
If I remember right, the BCM is responsible for those functions.  Hmmm...

Steve, I am definitely interested in a DIY cable for VPW communications. 
  Unfortunately I'm not sure if the BCM/IPC messages are documented or 
not.  I've never seen them documented anywhere.

Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI pending)
1999 Oldsmobile Bravada, 4.3V6 CSFI (wife's truck) <- being a pain

Steve Ravet wrote:
>>-----Original Message-----
>>From: gmecm-bounces at diy-efi.org 
>>[mailto:gmecm-bounces at diy-efi.org] On Behalf Of Jay Vessels
>>Sent: Sunday, January 08, 2006 9:39 AM
>>To: gmecm at diy-efi.org
>>Subject: [Gmecm] Class2 DIY tools?
>>
>>Hi there!
>>
>>Are there any consumer tools that will talk over the Class 2 
>>bus on a GM
>>  light truck that will communicate with the IPC and BCM?  
>>I'm thinking of tools that would do some of the tests that I 
>>can do with a Tech2 (i.e. command IPC to turn on/off 
>>indicator lamps, command fuel guage to full or empty, read 
>>BCM DTCs, etc.)  I haven't done an exhaustive search, but it 
>>seems most tools outside of the Tech2 will either only read 
>>and clear DTCs, or they are geared to primarily gather 
>>powertrain data.
> 
> 
> Jay, how DIY do you want it to be?  Darren and I are working on a USB
> <-> VPW cable, with scan tool/reflashing software that runs on the PC.
> The cable is straightforward, the scan tool software maybe less so.  Do
> you know if the BCM and IPC communication messages are documented in the
> SAE specs?
> 
> On full size pickups (SBC vortecs, that is) the fuel gauge is driven by
> the PCM, not via class2.  Are you sure yours is class2?
> 
> --steve
> 
> 
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