I understand that early 00's GM vehicles(Corvette in particular) use the 1850 class 2 bus for a lot of the PCM/BCM and instrument cluster data. My question is, does the instrument panel continuously query the PCM for fuel/water temp/etc data? Or does the PCM transmit this data continuously without being requested?
If the instrument cluster requests this data, is the data stream look the same as if you request it with a scan tool, other than the source ID?
Can someone tell me where I can find the messages sent to the instrument cluster on the J1850 class 2 bus? I am specifically interested in the messages sent to the Corvette HUD unit.Originally Posted by matthud
Thanks,
-Scott
What year Vette? In any case the messages are continously broadcast.
Generally the data is in "proprietary" message formats and contains exactly what is required for the specific address.
Last edited by LSX378; 03-03-2010 at 12:34 AM.
1998
Ok then you will probably be fine with some J1850 compatible hardware to listen to what is on the bus and figure out what is what.
Unfortunately I don't have a vehicle to sniff on. I just have the gauge cluster that I am planning on using in a project vehicle that uses a standalone ECU.
Connect them up and cross your fingers. If the standalone ECU is the same or similar year GM.
Nope, the ecu does not follow the J1850 standard. Which is why I need to know the commands so I can process the ECU data and output the data to the cluster in the J1850 format.Connect them up and cross your fingers
It's a HUD from a 2005 vette that I am trying to interface to another vehicle. I don't actually have the vette. I was hoping to use some ELM322 based tool to collect the J1850 commands from a vette.
I can probably get access to a Vette, but is the instrument J1850 (class 2 serial data) the same bus that is on the OBD-II connector? If no, where can I tap this bus without tearing apart the car?
Actually, the only proprietary message I'm looking for is the one that the vette sends to tell the instruments (and/or the HUD) that the car on. The HUD won't powerup without it. all other signals are direct wires (e.g. speed, rpm, etc).
Thanks,
-Scott
Have seen class 2 on pin 2 on the OBDII connector. With any luck it will be consistent on all GM platforms.
Can anyone post/or pm a raw ELM32x capture of the GM instrument J1850 (class 2 serial data) bus or pin 2 of the obd-II connector from a 2002 or later GM vehicle? Preferably a vette.... I only need the first 30 seconds, when the car is first turned on...
Thanks,
-Scott
05 and later Vette was CAN bus.
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OK then the HUD came from a 2003 vette. It's J1850. the can bus pins on the controller are not connected and it has the xc68HC58 interface chip to talk j1850.
I was able to find the message formats in the SAE J2178 books, and I am able to command the fuel level, oil level and water temp. But about 5 seconds after I command it, the gauges go back to the failsafe position. This is on a dash that is not connected to the pcm or any other serial 2 device. I believe its because the gauge cluster knows there is no pcm present, and this lack of comm causes it to reset the position. Does anyone know of a way to emulate enough of the pcm messages to the gauge cluster to trick it into thinking it is there?
Cool. What hardware / Software are you using to send the J1850 commands?
What terminal program are you using? Will it send a text file?
elm322 and a python script I wrote.
So you can use python to run a script to send the message at a one per second rate?
Yes, it basically automates the ASCII strings that you could send from Hyperterminal, loops them once every so many seconds to keep a steady display.
so you are all set to go
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