Trying to monitor the data bus with an ELM327

[DS106Q]

Since I'm not having any luck with the format for reading mode $06 data (see my other thread), I decided to try something different...

I found someone who has a scantool that can read mode 6 data so I thought I would use an ELM327 in "Monitor All" mode (ATMA) while requesting it via the scantool. This should solve the problem (and I'll post it in the forum for the next guy who is interested).

Thus, I opened a communications terminal program, set it to 38400 baud at N-8-1 and started sending, or so I thought, commands to the ELM327 chip/interface. The good news is that I get the "ELM v2.1" prompt followed by a > (as should be the case, so far so good). The bad news is that no matter what I type/send it always responds with a blank line then another "ELM v2.1", blank line, then another >

The datasheet says a simple test is to use the ATRV command to read the battery voltage. It's clearly sending it to the interface because I see the send and receive lights flash, but nothing other than the blank line then another "ELM v2.1", blank line, then another > is returned.

Regardless of what I send, whether a legit AT command, or just random characters all I ever get is the blank line then another "ELM v2.1", blank line, then another > that's all.

I know the interface is working because I have been using it with PCMSCAN's OBD Terminal to manually read codes and also when trying to determine the valid mode 6 strings (as I asked in the other thread).

Anyone have any idea what the heck is taking place here? Oh, and yes, I have attempted to issue (multiple) ATZ reset commands with the same result always returned.

[Tazzi]

Sounds like its not receive the actual command properly.

All ELM commands require a carriage return at the end for them to register.

You will also need to set the OBD Protocol before trying to send ATMA, since the ELM needs to know what OBD protocol it is using before it can start monitoring it.

[DS106Q]

Thanks for the reply! For whatever reason, don't ask me why, but instead of sending ATRV I sent 41 54 52 56 (plus the carriage return, 0D) and it immediately returned 12.6V.

Likewise, I can't send 01 05 (another example in the datasheet) for the ECT value. I need to send 30 31 30 35 (plus the carriage return, 0D)

This seems odd because the datasheet specifically states to open a terminal program such as Hyperterminal, set the data rate, and type AT style commands. I have always addressed modems with ASCII characters.

Is there some way to switch the input mode out of base-16?


In regard to the ATMA monitoring, you mention setting the protocol first. The datasheet says that the default mode is 0=Automatic, and that it'll search for it and set it automatically. However, I set it (via ATSP2) to J1850 VPW and ATDP confirms J1850 VPW. Do I need to do anything else? When I go into monitoring mode, it just sits there listening and doesn't display anything. If I press a key it says STOPPED (just like the datasheet says it should) so I think it's entering monitoring mode correctly.

[antus]

ELM327 2.1 could be anything... I am not going to say that what you are trying to do won't work, there is every chance that it will work to some degree. But just a note to say ELMs and ELM clones and ELM alternative implementations generally do not do a very good of monitoring the bus, if at all. If you are serious about what you are doing you are probably better off getting a J2534 tool and using universal patchers logger to monitor the bus.

[ironduke]

What program are you using for a terminal program?? There may be a setting that is off..

[DS106Q]

@antus: Thanks for the heads-up! I'm new to all this, and all I'm really trying to do at the moment is read a couple of mode 6 test values. However, I do have access to a VXDIAG VCX Nano. It claims to support J2534, any idea if it'll work for monitoring the bus as a J2534 tool? As for "universal patchers logger" I'm not sure what that is, but I'll certainly look into it.

@ironduke: I settled on a program called CoolTerm because it's portable and free. However, I tried two others (RealTerm and SimpleSerial) and they both yielded the same responses, but it's certainly possible all three have the same default settings, so what value(s) are you thinking might need adjusting?

Also, I now understand why I kept getting the ELM chip version along with another prompt as described in my original post. For some reason, the ASCII characters are essentially ignored/stripped and it was using the 0D carriage return to repeat the last command (which was a reset upon booting up) so it was displaying that info over and over again. Now, I see that once a valid command is received (other than a reset) it doesn't display the chip info, just returns a > prompt.

EDIT: Universal Patcher --> Whoa!! This looks like a serious rabbit hole!

[gmtech825]

torque pro can read mode 6 data with the elm. it's a cheap app

[DS106Q]

@gmtech825 Good to know, thanks. I don't have a bluetooth ELM interface (though I know they can be had cheap). I have access to a professional scantool that can read them when needed, but would really like to be able to do it myself. All of this has just got me more and more curious and interested in all this and now I would really like to know the mode 6 syntax.

[ironduke]

I just downloaded and tried coolterm and it works fine with the first elm327 I grabbed, a bluetooth 38,400 baud unit claiming ELM 327 v1.5. Default settings used other than changing the com port and baud rate.

EDITED!!!! Hold everything..
with coolterm... Click on the view button on the upper right, then change to plain view.. Guessing you had hex view selected somehow..

Now you should be able to use regular ascii..

[DS106Q]

@ironduke: Thank you for testing this for me, awfully kind of you! Seems like there must be something wrong with my interface (despite it working fine with PCMSCAN). As far as I can tell, the plain text and hex in the upper right is just a way to view the terminal screen (great for hidden control characters). I'm in plain mode and still can't get mine to respond with ASCII commands. So...

To confirm, you can start CoolTerm with the ELM327 interface connected, set the baud rate, data bits, etc. then just enter a command via the keyboard, for instance, ATDP and press enter (CoolTerm defaults to sending CR+LF) and you'll get a response from the interface, is this correct?

Edit: Something else I noticed... When attempting to send ASCII characters, the send/receive LEDs on the interface don't blink (the software LEDs at the bottom right of CoolTerm do). When I press enter and it sends the 0D (or 0D+0A) then all the LEDs on the interface blink (but the interface acts like all I sent was the carriage return). Is yours like this or do you get the hardware LEDs flashing with every keystroke? Also, similarly, I don't get any of my keystrokes echoed back to the terminal (unless I set CoolTerm's local echo option on), the ELM327 has E1 enabled so I'm guessing I should be seeing characters as I type them. I would greatly appreciate it if, when you have a moment, you could check yours and let me know how it behaves.

@antus: Thank you so very much for pointing me in the direction of using Universal Patcher! I have downloaded it and, as you mentioned, the logger looks exactly like what I need. Plus, there are so many other cool functions that I decided I needed my own VCXNano (says it'll work with one) so I just purchased one and will continue this (and much more) once it arrives.