Hacking the GM Low Speed LAN


Goblin Guru
I want to hack into the GM Low Speed LAN for a few reasons.
- to find & fix my intermittent instrument cluster gauges issue
- add an oil pressure sender to my HP Tuners logs, and a new dash gauge.
- be able to add future functionality similar to what BradR has done.

Today I had some success.
My oscilloscope is showing data on the GM Low Speed LAN when my instrument cluster (IC) goes dead.
So I'm guessing that some data is missing that the IC needs.

I went and bought a CAN BUS module for an arduino, did a little circuit board soldering, then plugged then into my PC.
I was able to modify Mike McGuire's code, to read the GM Low Speed LAN.


Now I am hacking, by logging events at specific times, then looking for the event in the data.

Playing. Having fun. Hacking.
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Goblin Guru
The GMLANs (both high speed and low speed) both go to the OBD port, so they are the same. Same speed.
The high speed LAN bounces thru each computer, so there would be a little delay from one end ot the network to the other,
but the low speed LAN is direct to each device.


Goblin Guru
The low speed GMLAN is the 33.3Kb/second green wire that goes to the BCM, OBD, gauge cluster, etc.
The high speed GMLAN is the 500Kb/sec brown and tan wires that go to the BCM, OBD, power steering, PCM.

I haven't hacked the high speed LAN yet, but the hardware I have can do that too.
In 2006, my donor was pre-CANBUS, but the GMLANs were the pre-cursors to it. I think 2007 followed the CANBUS protocol.
The hardware I bought is made for CANBUS protocol, but can be modified to talk the slower speeds of my 2006 GMLAN.
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Well-Known Member
Year model difference. Got it. At first I thought that seemed like a lot of work to get data that should be trivial to access.