Okay...

As described in this thread, I was able to solve my immediate problem just by taking my car down to AutoZone and have them clear the code for me.

But the code has come back a couple of times. This last time, it came back about an hour after they cleared the code for me, and I'm now embarassed to go back so soon.

I always tighten my gas cap so it clicks properly (as printed on the cap itself), but yesterday when I filled the tank, I noticed that the cap was slightly easier to unscrew than I think it should have been. I think thermal cycling loosens the gas cap a bit on this car. Again, nothing I can do about it other than to tightent it carefully at each fill-up, but that won't make the tank pressure sensor stop "falsing" in the early summer.

I was shown an OBD->Serial connector cable at the owner's meet, and the conclusion was reached that there aren't any electronics needed in the interface, just the proper pinouts and the proper software at the PC's end.

When I do a web search, I only come up with commercial sites that are SELLING the connectors and software. No way I'm spending hundreds just for a connector and some software that should be open-source in the first place.

Does anyone have a link to a site that (a) has the connector pinouts diagrammed, and (b) has freeware and/or open-source software for this?

I am not sure if this is the best out there, but it kinda fits what you were asking for. It will take a little work though.

Here is some hardware stuff.
And here is some software stuff.
It is an old bookmark I had from the last time OBDII came up.

Thanks for those links. This directly contradicts what I saw last weekend at the meet. What I saw was a plain interface cable with OBD2 at one end and RS-232 at the other, no intervening electronics needed.

So what's right?

I would not use a plain interface cable.. there probably is some electronics in whatever cable you saw.. either that or the owner is an idiot.

the ODBII interface is car voltage.. 12-13v.. but the serial port is 5v.. atleast that's what I remember.. it's probably a good idea to use some kind of regulating adapter.. some ODBII cables i've seen have optical isolation.. also not a bad idea when hooking this stuff up.

The cabling we saw at the meet didn't seem to have enough room anywhere for the amount of electronics posted above.

Hopefully the owner of that cable we saw at the meet will step forward here and help out. Would be interesting to find out if there was electronics inside one of the cable ends.

I apologize for not remembering who-was-who at the meet. I'm terrible with faces and names.

That's a nice hardware solution - with good kit options, pcb only ($15), the uncommon parts ($19), or a fully built unit (~$75).

I wonder how good the software is?

I might look into getting it as a kit if I can't find any simpler options.

As far as the software is concerned, I only need it to read and optionally clear codes for me.

Hey, the software looks reasonably good, although I'm not OBD expert. It will clear codes for you though It is also free, and has a self-contained demo mode that can be activated if no interface/vehicle is present.

I didn't know about the self-contained demo mode. I downloaded the software but did not try installing it.

Tony,
You might want to replace the cap. Most gas caps on newer cars have a check valve of some sort built into them to allow air in, but not out (IIRC). This is so that any vapors that build up will be forced through and captured by the evap canister, not directly into the atmosphere. Occasionally they do go bad.

Cheers
Phil

Interesting, perhaps I just need to take the car down to the dealership and make them replace the gas cap under warranty.

Still a big hassle since the dealership is a 35-minute drive away.

I apologize for not remembering who-was-who at the meet. I'm terrible with faces and names

Same here, I only really remember Dionysus from this meet, all due to us zipping along the roads of San Fran for a while

Definitely, if it's still under warranty. It could be that or something related. Either way, you should not have to pay special attention when tightening the cap... just click and done.

Phil

I'm the idiot.

The cable has no electronics in it, just straight connections. However, it does work (sometimes). After fussing with it for about 2 weeks now I've decided to send it back and try something else. This cable is way too flaky for me, and I tend to agree with your post about having something with regulating circuitry. Definitely something more robust than this. Oh, and BTW the one I have is the ISO connector from ODB-2.com / Alex Peper.

RS232C ports (theoretically) use +/-12v signalling, in practice I believe the specificaction is quite tolerant (+/-18v?)either side of this. A lot of notebook PCs and handheld devices can only manage to drive their RS232C ports to +/-5v which I think is where you've previously heard the 5v thing?

Well, the kit linked earlier in this thread looks good, and I messed with its freeware software and that looked really good, but even the kit ends up being about 50 bucks in parts (the PCB is a separate purchase from the rare-parts package).

So I bit the bullet and made an appointment with the dealership to look at why it keeps falsing on me.