Would it be possible to record/copy/emulate data communication ?

[Externet]

Two devices, as an error code reader and a dedicated computing device similar to an ECU in an automobile talk to each other to retrieve data and place commands.

Being such specialized code reader expensive, I wonder if a laptop could be tapped onto the data lines and record the handshaking and the data transceived for every command.

Example: At plug in, recording the handshake.
When key number 1 in the reader is pressed, record the command.
When the 'ECU' responds, record the data.
When key number 2 on the reader is pressed, record the command.
When the 'ECU' responds, record the data... and so on.

With all that recorded in the laptop, emulate the same process without the dedicated reader device, using the laptop instead.

(The reader device for the example is not a ECU reader; the device has multiple applications but only one is needed and does not justify the cost)

What would be the way to do it ? Is any existing application being used for similar task ? Tapping hardware via USB, parallel or serial port ?

 

[cowboybob]

Doable.

You'd have to figure out the query, command and return data packet configuration(s). Probably somewhere on the net.

OBD2 comms are serial (RS232).

A "hyperterminal" like app would suffice but would be very crude.

The standard OBD2 data points are well documented, but the manufacturers' specific codes and commandable points are very difficult to get (as you would expect).

Other problems arise, i.e., incompatible RS232 to USB chip sets, and exacerbated by the auto industry's lag time in implementing current comm chip firmware versions.

 

[Externet]

Thanks.

...but the manufacturers' specific codes and commandable points are very difficult to get...

That is the point. Instead of looking for the unobtanium, just record the data with a rented reader and then emulate with the laptop. Any 'hyperterminal'-like you would suggest ?

 

[cowboybob]

Well, it always sounds easy to merely record the incoming data and emulate, but...

There are always specific commands needed to get the ECU (PLC, whatever) to respond. Generally it's not just a single "read" command but a "read" with a specific data location director and often surrounding code that the manufacturer slips in.

Of course, sometimes not.

But at the very least you have to determine what command will get the device to talk back to you.

And, of course, you've got to figure out the data protocals such as baud rate, parity, stop bits (if used), etc.

Good luck and let us know how it works out.

Any emulator that matches your operating system will do,

 

[ClydeCrashKop]

I remembered these guys https://elmelectronics.com/obdic.html and went looking for them and found this, so I bought one.
ELM327 V1.4 USB OBD2 OBDII CAN-BUS Diagnostic Scanner USB Cable Price $15.99

https://www.amazon.com/ELM327-OBDII-CAN-BUS-Diagnostic-Scanner/dp/B005FEGP7I/ref=pd_sim_auto_4

 

[cowboybob]

For this device, be sure to read the comments before you buy it (pros and cons).

And remember, this is only good for the basic, mandated OBD2 error codes (which you'll have to look up for the meaning of the code) - NO manufacturer specific codes are included nor is there any functionality beyond reading error codes and clearing them. No command ability.

 

[Externet]

Thanks.
Did read the fine print, found that much other things are to consider with that interesting product.
But there is command ability. If instructs to clear codes, it is sending at least that command.

 

[cowboybob]

...But there is command ability. If instructs to clear codes, it is sending at least that command.

True. But only within the confines of the OBD2 mandated protocals.

And, of course, per your original post, without further instruction sets there is no way to force data recoding.

Here's an interesting exchange I found with a google query of "OBD2 Ford command codes" (I only chose "Ford" as an example...):

https://teamzx2.com/threads/34213-Toggle-an-actuator-directly-from-an-OBDII-scanner

Note the coding required.

 

[ClydeCrashKop]

This is open source. You can find a lot of info on the web.
Page 40 of this data sheet
https://www.electro-tech-online.com/custompdfs/2013/08/ELM327DS.pdf
says you can tell it to "Monitor All" and it will tell you everything that goes over the data bus. CAN will send too much information. >AT MT 10 instruction will limit it to just what the ECU is saying.
You just need to find documentation to interpret the data. I.E. J1939 is one they mentioned. Maybe its on the ELM website.