Jza

Anyone know of some scanning software that would work on a 98 Camaro and 98 Corvette? Maybe with the MAX232 cable..?

I appreciate any help on this. Thanks.

Grumpy

You might try *The Turbo Shop* out in Socal.
I doubt you normal cables will work with OBDII

Hmm,

might try OBDII.com or something like that he did have early stuff (ie 96 MY)

Jza

Thanks for the lead Grumpy. I'll check that out. I just noticed the circuit diagrams for the MAX232/233 cables on Craig Moates' site show the pins for 95+ OBDII as well as our OBI plugs, so I guessed that *someone* somewhere had been messing with that and could point me in the right direction.

Jza

I just noticed the circuit diagrams for the MAX232/233 cables on Craig Moates' site show the pins for 95+ OBDII as well as our OBI plugs, so I guessed that *someone* somewhere had been messing with that and could point me in the right direction.

ttt

Grumpy

There are some OBDII that share with OBI. To universally say which is who might be in error

94ZRagtop

The MAX232 circuit won't work with the '98 PCMs. The OBDII datastream is a completely different animal than the OBDI datastream. I'm going to compile a web page with this information, but here is some technical details about OBDII, and the differences between OBDII and OBDI.

Sorry it's so long, but this is the first 'public' post of all of this information, any feedback would be appreciated.

-Andrew

If you're looking to communicate with an OBDII PCM, here are some options for you.

First, a document describing the OBDII 10.4Kbps datastream structure that GM implemented:

http://developer.intel.com/design/in...s/j1850_wp.pdf

Interested in rolling your own diagnostics software?

http://www.multiplex-engineering.com sells inexpensive ($70-80) OBDII interfaces for GM (VPW), Ford (PWM), and Chrysler (ISO). They will sell you the converter box, and provide you with the protocol document that allows you to talk to their box. The only thing you'll need to provide (heh heh) is the SAE paperwork that tells you what to request and how to decode it. They don't actually provide you with any OBDII docs, just how to talk to their box. As a side note, this is the same interface that the Palm based OBDII software that you see popping up everywhere (like at http://www.aeswave.com ) is using. However, each M-E box has their own 'hardware address' that you must poll with the serial port message, and although I have not asked, I'd bet that they dedicate a hardware address to each Palm software vendor. For example, AESWave's software is looking for a M-E device at address 0x80. Unfortunately, the M-E device I bought has address 0x55, so it doesn't reply to the AESwave software query.

If you don't want to go so deep in writing your own code, and want to work on a budget, Alex Peper's CarCode is an excellent option at http://www.obd-2.com It's reasonably priced, and is good for pulling diagnostic trouble codes and some sensor data. It doesn't have the manufacturer specific data for most vehicles, but it does for the important ones (LT1 and LS1 heh heh my personal favorites). Worth a look. I bought a copy of this on a GMECM group purchase a couple of years ago.

If you're more interested in a professional package, AutoTap at http://www.obdii.com or Ease Diagnostics at http://www.easesim.com are also popular. They do pull manufacturer specific trouble codes. I also have a copy of AutoTap. Can't have too many scan tools. These are turn-key, and are priced in the $250-$300 range.

Then another one is EFILive - looks like v5.0 supports OBDII with an interface that they provide. I downloaded the software earlier this week, but don't have the interface, so I was just looking at it for now. See it at http://www.starrperformance.com.au - looks interesting.

As for TTS Datamaster (http://www.ttspowersystems.com), in the spring, they do hope to introduce Datamaster for OBDII. I'm hoping to have a beta copy of it as soon as they have one available (in a month or so, I hope! ). My biggest complaint about OBDII is the bus overhead and the very slow 'data frame' rate, and TTS is designing their software to maximize the amount of relevant data per frame - so they get higher performance (more data per second) with their scan tool than, say, AutoTap.

If you're looking for *just* some OBDII interface chips to build your own scan tool, then these chips may be the ticket for you. Pay particular attention to the .PDF file here, it has some very good information in it.

http://www.elmelectronics.com/Produc...ct/Connect.htm

http://www.elmelectronics.com/Produc...s/ELM322DS.pdf

Interesting tidbits there. For anyone wanting a hard core kit, there it is.

> What's 1X vs 4X modes in OBDII? I take it a standard AKM cable won't talk
> to OBD-II ?
>
> Help me understand here

OK...

OBDI is *simple* compared to OBDII. It operates at 8192 baud, 8 - none - 1 encoding. All you need is a voltage to voltage converter (a la AKM cable) to translate the 5 volt ALDL bus wire to the RS232 compliant Transmit and Receive. That's it - voltage to voltage conversion. The rest is all software.

Now, for OBDII. GM OBDII (which is the only one that matters, right? ;^) ) has two modes - 1X - which is 10.4 kbps, and 4X - which is 41.6 kbps. OBDII Scan tools (AutoTap, Ease Diagnostics, etc) *only* operate at 10.4 kbps. That is GM's standard diagnostic bit data rate. Now, it sounds like being a kbps, that it might be RS232 compatible? Nope. GM uses Variable Pulse Width - I don't remember offhand which is which, but take this example. A logical low short pulse can be a zero, a logical low long pulse can be a 1. A logical high short pulse can be a zero, a logical high long pulse can be a 1. So, to send a byte of data, there is a voltage transition for every bit - high, low, high, low, high, low ad infinitum. The width of the pulse determines whether it's a 1 or a 0. Now, with RS232, you can have two 1's next to each other, and the voltage state of the two bits will not change between the two of them (I believe a 0 in RS232 is +3 to +12 Volts, and a 1 in RS232 is -3 to -12 Volts) - so you can have (+V) (+V) (+V) (-V) (+V) (+V) being a valid sequence of bits in RS232. Also, the OBDII data wire is transitioning between +12V and 0V (or thereabouts). So, due to the variable pulsewidth, you *must* have some sort of translator microprocessor between an OBDII data bus and an RS232 device.

And the 41.6 kbps (4X) mode is used for reading from and writing to the flash memory. It's also known as programming mode. If a chip or cable can't do 4X mode, it can't be used to program a PCM. Carputing designed their own cable (I'm building some this afternoon, in fact) to do this. It has to be capable of switching from 1X to 4X and back. It took Dave a good deal of design time to hammer it out, but it works slick. To date, the guys at http://www.carputing.com are the only ones who have a working, publicly available, <$1000 programming cable for OBDII, but it ONLY works with their software, and it ONLY works on LT1 and LS1 vehicles.

A standard AKM cable, therefore, has no chance of talking OBDII, because of the VPW.

Now, for the exception to the rule.

Peter Gargano wrote a quick and dirty DOS based utility to extract trouble codes from an OBDII vehicle - using the handshake lines of the RS232 port and 'bit banging'. Essentially, he samples the RS232 port to measure the time interval between pulses, and determines whether or not it's a 1 or a 0. However, he requires a rather quick computer to do the sampling (he uses a 500 MHz PIII - I could not get it to scan on a P1 133MHz machine). Although this is a novel approach, it's prone to errors and dropped bits, so I'd never use it for programming. But it supposedly works for getting trouble codes (I've never gotten it to work, even on my desktop Athlon 600).

Jza

dude.........


Thanks a lot. I think I'll be able to figure something out from some of that. Muchos gracias.