[Gmecm] Class2 DIY tools?

[Jay Vessels]

Hi there!

Phillip, thanks for the detailed email. That one's going in the archive 
for sure.

Y'all won't believe what I found, but I have found at least a cause, 
though I haven't investigated it completely yet for a fix.

First, the problem with the alarm I mentioned when I tried it was my 
fault -- I didn't wait the 30 seconds it takes to arm the system.  Once 
I waited 30 seconds, the alarm sounded.  I tried some other BCM-specifc 
functions and they all worked, so I decided I probably hadn't murdered 
the BCM.

So, I decided that I had tried enough shotgunning of this problem and 
grabbed my meter.  I checked power and ground at the BCM and IPC, all 
good.  I printed some schematics out from the Techline CD and started 
staring at it.  It kept seeming like I had killed the Class 2 bus 
somehow -- no messages to the IPC, no Passlock message to the VCM.

I noticed that the Memory Seat Module was also on the Class 2 bus, so I 
decided to try it.  Didn't work -- it never moved the seat or chimed. 
Hmmm...  So, I'm sitting in the driver's seat with the key on, playing 
with the power seat switches (for no real good reason) and the fuel 
gauge takes off working.

So, I cycle the ignition key, and everything's lovely.  Hit the starter, 
and it starts and runs.

If I move the seat I can make and kill the Class 2 bus, so it sounds 
like I have a wiring fault in the memory seat module wiring under the 
seat.

Thanks for all the information on this one.

Jay Vessels
1982 Chevrolet S-10 Sport, 2.8V6 TBI
1984 Chevrolet S-10 Blazer Sport, 2.8V6 (TBI pending)


Phillip Kuhn wrote:
> Ok, I have reviewed the GM wiring schematics for this
> vehicle and this is what I can tell you. The BCM is
> NOT in control over the info coming into the cluster.
> The cluster recieves it's data via the class 2 data
> bus from the VCM (aka PCM) on this vehicle. Also, the
> passkey system in this truck does NOT go through the
> cluster, rather it is wired directly to the bcm which
> sends data to the VCM. More than likely from what I
> see in service information and from what you say the 2
> problems that you are having are completely separate
> and not related in any way, at least not by something
> such as the BCM. I can send you some "real" wiring
> schematics tomorrow of the cluster and passkey system.
> In the meanwhile my suggestions would be to first
> check ALL of the fuses as there are many that could
> affect the operation of the vehicle. Second attempt to
> perform a passkey relearn. And third, double check all
> of your connectors to make sure all of them are
> completely seated.I can assure you of this, when it
> comes to passkey in particular, there is NOT any way
> possible to perform certain functions without a tech 2
> and any other scan tool is not capable of performing
> those functions from what I have been told. Below is a
> key learn procedure borrowed from service information.
> 
> 
> 1. Ensure that the battery is fully charged. 
> 2. Use a scan tool in order to clear the Passlock?
> DTCs
> 3. Turn the ignition switch from the OFF position to
> the CRANK position, and then to the RUN position. The
> vehicle will start and then stall. 
> 4. Leave the ignition ON until the security telltale
> turns OFF in 10 minutes. 
> 5. Repeat Steps 3-5 for 2 more times (3 times total) 
> 6. The Passlock? controller will learn the new data on
> the next start 
> 7. Use a scan tool in order to clear all DTCs. 
> 
> I would at least attempt to do the key learn without
> clearing the codes as I have never had to clear them
> before programming a key. Be sure though, if you do
> attempt a key relearn that your battery is charged
> because if it dies in the middle of a learn it is
> possible to ruin the passkey module.As far as possible
> "common" causes of your original symptoms they would
> be : loss of vcm to cluster communications, blown
> guages fuse, bad vcm, or bad cluster. Those are about
> the only things that would cause the original
> symptoms. As far as the new problem you induced it
> could be a number of problems relating to the passkey
> module, bcm, vcm , wiring, fuses, or just simply a
> lost password. I hope this sheds a little more light
> on the situation,
> Phil