Confused Newbie

**fatejd** · 10-31-2006, 01:14 PM

I guess I'm still debating whether or not to actually get a OBD device. I guess it would be nice to be able to see some information about the car, but for the most part I don't see the use for it for some one like me (not a gear head). I know you can turn off indicator lights and such and there are car specific things you can do (I was at the dealer the other day and the service guy didn't know what one of the options was - made me laugh). I dunno if some one can (or already has) run down the basic functionality of using a OBD device for a light user such as myself...

Thanks

**michbound** · 10-31-2006, 01:40 PM

Well for a lightuser you could just run down to Murrays or any local autostore and they will loan you an OBD II code reader for free (at least my Murrays in Michigan does this), can't get any easier than that.

Paul
www.obdpros.com

**digimotojoel** · 10-31-2006, 03:22 PM

You can find OBD coder readers on eBay for $30. I have always been a supporter of the ELM product line, even though it may not be the fastest, it is a good hobbiest tool... at a good price.

**air1kdf** · 10-31-2006, 10:05 PM

Wow, a lot of life left in this old thread.

All computer people understand bandwidth. The mongoose has it, no doubt about it. Where some people are getting confused is the difference between MAX bandwidth and actual bandwidth. I guarantee that a car will crash if it used all 500k bandwidth of the bus.

Any interruption on J2534 will make your car run like crap at best. The elm can't make that happen, no matter how bad that the software on the chip or talking to the chip is. This is the strength and weakness of J2534.

Change just one bit in the computer, and you have voided your engine warranty, possible the drive train warranty as well. If you interrupt the bus in any way you have also voided your warranty. If you don't believe me, ask your local car dealer. You can also email or call Ford, Chevy, Dodge, Honda, Nissan, Mitsubishi, etc. and ask them.

J2534 is not for just listening.

We could debate for a while, but I don't think that it's worth the aggravation. In the end, I seriously doubt that the mongoose belongs in a car PC. Unless I'm just totally missing the point, why would you want to have a re-programmer in a car PC? I have no doubt that the mongoose is excellent hardware.

So are you using an ES chipped Car PC also? Sweet!

**Headsex** · 10-31-2006, 10:15 PM

a J2534 Interuption will not worry the PCM at all, the car will behave as its supposed to. I've done it many times. Done some dataloggin, and unplugged the cable whilst it was spewing data out.. the software i was using crashed yes, but the continued to drive fine. as expected!

d

**air1kdf** · 10-31-2006, 10:46 PM

Originally Posted by Headsex

a J2534 Interuption will not worry the PCM at all, the car will behave as its supposed to. I've done it many times. Done some dataloggin, and unplugged the cable whilst it was spewing data out.. the software i was using crashed yes, but the continued to drive fine. as expected!

d

Don't you mean did not in your case. Both Joey and I have seen a car's computer crash first hand, not pretty.

**michbound** · 11-01-2006, 09:58 AM

Originally Posted by air1kdf

Don't you mean did not in your case. Both Joey and I have seen a car's computer crash first hand, not pretty.

I would be curious to understand why this would be the case; J2534 is just an api that allows you to talk to the vehicle, the data you send is still identical to the other scantools in most cases, of course you could crash the computer while reprogramming but if you use the mongoose or any J2534 compliant tool to just get at sensor data I do not see any reason for it to crash the PCM, maybe I am missing something so can you go into some details?

Maybe Joey can elaborate here also?

Paul
www.obdpros.com

**air1kdf** · 11-02-2006, 06:31 PM

Paul,
First off if you are the guy that wrote his own elm compatible scan tool, let me say, you are the man. I actually need to get one of your units for personal use as long as it works with elm commands. Please email me.

Well you should know more about this than I do. It has always been my understanding that it is different, particularly that it has a higher priority, which is also why it can get messages at a much faster rate. I am only going from memory from a few years ago when I was knee deep in the specifications when I was going to write a very special chip for Harley Davidsons. It wasn't worth my time in the end, so I just bought an ELM chip.

**michbound** · 11-03-2006, 04:48 AM

Originally Posted by air1kdf

Paul,
First off if you are the guy that wrote his own elm compatible scan tool, let me say, you are the man. I actually need to get one of your units for personal use as long as it works with elm commands. Please email me.

Well you should know more about this than I do. It has always been my understanding that it is different, particularly that it has a higher priority, which is also why it can get messages at a much faster rate. I am only going from memory from a few years ago when I was knee deep in the specifications when I was going to write a very special chip for Harley Davidsons. It wasn't worth my time in the end, so I just bought an ELM chip.

Hi air1kdf,

Thanks; getting a micro to recognize all the protocols is'nt that difficult it just takes a lot of time pouring over the specs as you mentioned

.

Yes the OBDPro uses the same command set as an ELM this allows the OBDPro to be compatible with all the ELM software out there. check out the OBDPro datasheet .

Do the Harley Davidsons just use the VPW protocol? Also are the commands similar to the ones used by GM vehicles i.e do thay use the same/similar modes and pid's?

Re The J2534 I am not very familiar with the spec, I had read the spec once when a company had approached me to do some work for them using a J2534 interface - that project never materialized, but when I had read the spec my impression was that it was just an API, so that any OBD/reprogramming software written to the API would work with any hardware that implemented the J2534 API layer

I think one could even claim that the ELM is J2534 compliant if one was to write an abstraction layer that converts the J2534 api entry points into equivalent ELM commands. Sure most of the low cost tools might not be able to support the high speed programming mode but for most part when it comes to reading sensors etc it could be made J2534 compliant.

Paul
www.obdpros.com

**joeyoravec** · 11-04-2006, 02:13 PM

Yes, we're just talking about an API (driver DLL). You could make a driver for some of the low-cost tools, but the elm327 can't support most of the useful I/O control function calls. It wouldn't come close to passing a J2534-3 compliance test.

And from 3 posts ago, no -- unplugging the cable, requesting data (properly), and almost anything cannot crash an ECU. An OBD-II conformance test (J1699) checks many of these things, and the US EPA requires any vehicle to pass this test before sale. It is possible to cause problems if you use a crappy vehicle interface that causes network faults, but if you remain within the specs there is no problem at all.