[b3lha]

The absolute best way to troubleshoot communications is with the Hex Com Tool.

Send a command eg. "78123400" and observe what the ECU sends back. It should be three bytes repeated over and over, the first two being the address and the last being the data. Something like "123400123400123400123400.....". If there is any corruption then you need the "92 problem" comparator board.

I haven't tried the port monitor software myself, so I can't comment on that.

The VWRX software is great, but it does have some bugs, which we can't fix without access to the source code. It does not seem to clear the input buffer when sending a new command, nor validate the data being returned. So if there is any data left in the buffer from the previous command then it assumes that is the reply from the current command.

I also suspect that it polls the port rather than being interrupt driven. That means the program repeatedly asks the interface if there is any data available rather than the interface informing the program when data is received. Reading the data using polling can cause a loss of sync if the buffer overflows in between polls.

My linux software, while is isn't pretty or user-friendly, goes to a lot of trouble to ensure that the data returned is accurate.