02 Impala 3.8L Scanning

[Vince Black]

I have what some might call a stupid question, but first a bit about my background. I have been a mechanic for years, I also do some web programming, java, cpp, and a lot of other assorted, weird, technical things. I have a bunch of different automotive electrical diagnostic tools, snap-on obd1 and obd2 scanners, snap-on DVOM, just all sorts of tools and experience. I was recently reading on the web about re-flashing and always thought it HAD to go to the dealer to do it. Well, except for buying some $6000 manufacturer specific glorified PDA. So, knowing that a PC power supply puts out 12 and 5 volt DC, and knowing the wiring of a PCM is nothing for me to fear, I made my own little test bench from where the T.V. USED to be in the living room. Man, my girlfriend is PISSED, so anyhow, I got a used PCM from a 02 Impala 3.8L. I have it hooked up to a floppy plug from a power supply and have it wired to one of my less expensive OBD2 scanners, just in case something happens to get fried. No problems, scanner comes up, got a perfect data stream, codes, tests, etc. Now that I get to asking the question, I realize how wired on coffee I am and didn't need to explain half of that stuff. Is there a way I can cut and splice either a printer plug, or a USB plug into where the DLC would be and be able to do anything using just a PC? Or would I absolutely have to have something between the two as an interface? I have read about the tech 2 although I have not used or owned one, I have read about the ELM 327 chip, and the CarDAQ pass-thru for J2534 standards, but I suppose the second part of my question is this - Why would you need a programmer to be a stand alone piece of hardware when theoretically (at least in my mind) I would think you could create a software based emulator to take place of the pass-thru interface and just connect the USB port straight to the PCM and get to flashing it. Sorry for such a long post to get to the point, but I have not been getting much sleep lately between work and reading for 8 hours a night about flashing OBD2 PCM's. I am excited about it though and once I get more into it I have no doubt I can at least help this community with feedback about other things.

[antus]

The interfaces are more of an electrical adaptor that can convert the car signals in to rs232 serial for the pc. USB has its own rather complex protocol regarding how many and what devices are on the bus, data bandwidth and power draw for each one as well as timing so that multiple devices can co-exist, even if you only happen to have 1 plugged in at the time. Most interfaces tell the USB bus that they are an RS232 adaptor and provide the USB specific stuff to the pc side, while interfacing the car interface on the other side. Their purpose is more electrical compatability and the handling of the data is left to the pc.

Due to this you will need some kind of interface and wont be able to wire usb directly in to the car data line. The interfaces you mentioned can be found relatively cheaply and would be the way to go if you want to look at flashing your car ecu from the pc. You'll then need the right the software for your ecm, but being in Australia I dont know what that is. Perhaps one of the USA guys are here can point you in the right direction.

[Vince Black]

Thank you for moving my post, I must have been sleepy and putting it in the wrong spot. I pretty much understand everything you wrote Antus, thank you for clearing it up. I just thought for some reason it would be possible and easier to use software emulation instead of a hardware interface. I don't mind spending the money on something if it will work right, I just didn't see a need if it could be done by simplifying it down to just a PCM, USB cable and a PC.