EngineerSteve

I have interfaced to my older Ford vehicle using J1850 PWM. Now I am working on CAN in a newer vehicle. I own a copy of J1979 but am a little confused about the header for CAN PID value requests.

Here is a sample request for RPM in J1850 PWM (in hex of course):

request:
61 6A F1 01 0C crc
response:
41 6b nn 0C aa bb crc
where nn=ECU address, aa bb = DATA A and DATA B

Can anyone give me this same example in CAN?

Thanks,
Steve

MP3Car.com

 

p2psmurf

In PWM 61 6A F1 is the header.
For Can the header will be setup by the can-chip. All you do is supply a address where to send it, either 11-bit or 29-bit.
The data is the same as for any other protocol: 01 0C.
See page 22 of you manual.

Aberk

for 11bit its 0x7DF for the functional addressing or (typically)0x7E0 for the physical address of the Engine computer. The response from the Engine computer is typically 0x7E8.

What tool are you using to do the requesting?

EngineerSteve

I am using a Multiplex Engineering T21 card attached to my embedded microcontroller. In the future I will use the CAN module on my embedded micro.

Steve

p2psmurf

With 11-bits can there's no guarantee that 0x7e0 is the engine.
Could be anyone from 0x7e0 through 0x7e7.

Aberk

That's why I said typically. It has been for every car in my experience, but I know there is no guarantee.

EngineerSteve

I have done more research and study on this issue. See if this looks correct:

The CAN message for RPM:

7DF 02 01 0C

7DF = The 11 bit CAN ID
02 = 2 data bytes used out of the possible 7 CAN data bytes
01 = Service 01
0C = RPM PID

What do y'all think?

Steve

Aberk

Looks good to me. Depending on how your hardware you may not need to put the 02.

MP3Car.com

 

Vitaliy

Here's a sample of actual communication b/w an ElmScan 5 scan tool, and ECU Sim (as reported by ECU Sim):


Is this a commercial project?

Best regards,

Vitaliy

__________________
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Vitaliy

By the way, CAN lets you increase the throughput by combining several PID requests into one, like this:

01 00 01 05 0C 0D

Vitaliy

__________________
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EngineerSteve

Vitaliy:

Thanks for the good reply. I begin to see what is going on.

The project is potentially commercial. I have an interest in this stuff and my company could possibly develop a vehicle based product that could use the data from OBDII.

Personnaly I would like to learn communications with vehicle ECU's, I think it is a career enhancer.

Steve

Vitaliy

My company (ScanTool.net) helped a number of companies integrate OBDII into their products. We also sell OBD cables (through obd2cables.com), connectors, ECU simulators (ecusims.com), OBD chips, etc., as well as providing consulting services.

If you would like to discuss this off-line, best way to reach me is via email, vitaliy(A)scantool.net

</end shameless plug>

Best regards,

Vitaliy

__________________
— Did you know that MP3Car sells OBD-2 interfaces? Get your ElmScan 5 Compact for only $64.95!
— Need to look up a diagnostic trouble code? Try the most up-to-date, free DTCsearch.com!

Aberk

I'll shamelessly plug them too. They really know their stuff and can help a lot.

MP3Car.com