OBD-II realtime data

casm · Sep 5, 2004

Question for anyone more familiar with the XJ's OBD-II implementation than I: what realtime sensor data is available from the OBD-II port? Is there something that details this a bit more extensively than http://www.go.jeep-xj.info/HowtoECUcodes.htm ? It's a good resource; it just doesn't seem to cover what I want to do.

Looking here, this guy is doing something I'm interested in (telemetry) via what look to be sensor outputs through his car's OBD-II port. Is this even possible on an XJ?

jldiaz · Sep 6, 2004

Take a look at www.obdii.com.
Have you found any doc on the communication protocol through the OBDII port? (i.e. how to pull info)
I have an AutoTap, and would like to use the interface from other programs.

casm · Sep 6, 2004

jldiaz said:
Take a look at www.obdii.com.

Yup, seen it. Problem is it doesn't cover manufacturer-specific extensions to the OBD-II spec. Telemetry is proposed as a part of OBD-III, but that's a long way off and has a lot of privacy concerns.

Have you found any doc on the communication protocol through the OBDII port? (i.e. how to pull info)
I have an AutoTap, and would like to use the interface from other programs.

My plan was to use Freediag and pretty much just reuse their code to pull the manufacturer-specific stuff.

ChuckstrPT · Sep 6, 2004

I'm pretty sure I've seen some software for both laptops and palm's for pulling info from the OBDII sensors, both problem codes and real time data. I know they have them for VW&Audi cars for a palm. I've got no experience with either form, but have considered the Audi version for our other ride, and since the acquisition of the XJ, also considering it for the Heep. Has anyone used these for the Palm platform?

jldiaz · Sep 6, 2004

Casm: I looked at freediag, and it looks like a good starting point. Haven't seen anything on manufacturer-specific cides, though. Right now, I'm trying to determine whether getting codes like 'P001A' is AutoTap's or the PCM's problem (or mine).

casm · Sep 6, 2004

jldiaz said:
Casm: I looked at freediag, and it looks like a good starting point. Haven't seen anything on manufacturer-specific cides, though.

That's about where I am with it, too. There's a fair bit of info on the standard codes as well as some of the manufacturer-specific ones, but I'm just not finding anything on how to real realtime data over the bus. Oh well.

On another note, I went ahead and ordered the OBD-II-to-serial cable from Harrison R&D. I figured that for $16 plus shipping it's a better deal than the cheapest OBD-II reader I can get since the software's free.

Right now, I'm trying to determine whether getting codes like 'P001A' is AutoTap's or the PCM's problem (or mine).

I had a reference for the Jeep P-Codes somewhere a while back. I'll see if I can't dig it up and post a link to it.

JoBo · Sep 29, 2004

I'm a jeep xj newbie but have the VAG-COM unit for VW products. It's fantastic but I think there's tables that convert the codes to the actuall trouble. That requires a database for each car. Actually he uses the ECM's number to match it with the codes. It's a fantasic tool for my jetta tid (drive by wire diesel) It has a function to check if a car is obd-II compatable and it says my 96 XJ is but that's all it will do. Where do you get the $16 odbII to serial adapter?

Thanks
JoBo
96 XY now with Banks header

casm · Sep 29, 2004

JoBo said:
Where do you get the $16 odbII to serial adapter?

The adapter came from Harrison R&D, but you can't just drop it straight to your serial port as they're not electrically-compatible (something I neglected to mention earlier in the thread). You'll need an interface to handle that; my plan is to use Andy Whittaker's for now, though that may change if I can source something a bit more local.

Also check out the following links:

http://www.obdii.com/
http://www.obddiagnostics.com/
http://scantool.net/
http://freediag.sourceforge.net/
http://autorepair.about.com/cs/troubleshooting/l/bl_obd_main.htm

JoBo · Sep 30, 2004

Thanks for the links. I'm going to try what software that's available with my vag-com "opto-coupler" first. I've spent a little time looking but have not seen it listed yet.

JoBo

mhead · Sep 30, 2004

I have a 1992 XJ I-6. Does it have a OBD-II port or is it too old?

casm · Sep 30, 2004

mhead said:
I have a 1992 XJ I-6. Does it have a OBD-II port or is it too old?

Too old... OBD-II was mandated for '96-on model year vehicles.

jldiaz · Sep 30, 2004

Back to the original question: Apparently, the PCM doesn't actually send a stream of real-time data and you have to loop querying for it. Just keep it fast enough.

casm · Sep 30, 2004

jldiaz said:
Back to the original question: Apparently, the PCM doesn't actually send a stream of real-time data and you have to loop querying for it. Just keep it fast enough.

Interesting. I wonder how fast it can reply to queries. Does anyone have hardware specs on the Jeep OBD-II implementation? I'm wondering if there are enough CPU cycles available on the OBD-II controller vs. data rate (9600 baud IIRC) to poll for multiple statistics at once.

jldiaz · Sep 30, 2004

It should have enough, since some scanners get the info. There are three processors: a 16-bit master, one 8-bit for spark and another 8-bit for fuel. (I can't remember where I read this). The AutoTap pulls the info fast enough to handle about 8 concurrent gauges at a reasonable refresh rate with an AMD Athlon 1800+ and DDR memory.

casm · Sep 30, 2004

jldiaz said:
It should have enough, since some scanners get the info. There are three processors: a 16-bit master, one 8-bit for spark and another 8-bit for fuel. (I can't remember where I read this).

Thanks, that actually gives me some ideas on how the internal bus is constructed. I'll do some digging and see if I can't pull any more info.

The AutoTap pulls the info fast enough to handle about 8 concurrent gauges at a reasonable refresh rate with an AMD Athlon 1800+ and DDR memory.

Sure, understood. I was thinking more in terms of the OBD-II unit - my concern was that I'd be able to poll it faster than it could send data, or that there might be a wait or reset state between each poll. From looking at the Autotap screenshot, it appears as though they're pulling most of what I want to see. I notice from the VIN displayed in that shot, though, they're taking info from a '96 Oldsmobile (I used the AnalogX VIN decoder to get this info). Hopefully a Jeep OBD-II unit will be able to do the same; I suspect it probably will.

OBD-II realtime data

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