"I can't connect. What's wrong?"
If we had a dollar for every time we got this question, we'd be retired by now and living on some tropical island.
So why do we get this question so often? Because there are exactly one bazillion different reasons why you might not be able to connect the application running on your laptop to the chip inside your ECU. Between those two end points there are device drivers, USB ports, our diagnostic cable, the diagnostic port (& pins) inside your car, wiring between that port and the ECU, other things attached to those wires in your car and then circuitry inside the ECU and even power being provided to the ECU and ground on the diagnostic port.
Over the years we have seen every single one of those things go bad in someone's random 20+ year-old car. The most memorable of which was one guy we went back and forth with for 20+ e-mails until he finally realized that one of the pins in his car's diagnostic port was actually loose and pushing out of the way when he plugged his cable in! So it looked fine and tested fine without the cable plugged in but once the cable was inserted, the pin failed to make contact because it was simply not beign held in position.
So there is absolutely no single answer we can give to that question. And it's difficult to even write up a complete troubleshooting guide because there are just so many different ways that any one of those things might be bad.
That said, here's an attempt to provide some sort of “debugging” flow chart to help.
<Place holder> - I'll work on this, I promise. But I wanted to get the page started as my reminder.
Thoughts for future work:
Have you ever been able to connect to this ECU in this car using this cable and this laptop before? - possible cable issue if nothing else has changed; particularly if this problem just started after having been able to connect and log fine recently.
Is the package new from us or old/bought from a third party?
If new from us, then it's very unlikely that the cable is bad and you should suspect other issues first.
If it's used, do you know if it's been able to connect recently? If not, then it could be an issue with the cable.
If you've never been able to connect, make sure the device drivers are installed. Check this
. Don't just assume. Pull up device manager and confirm that you get a new COM port when the cable is plugged into the laptop.
Is the ECU even running? If the engine starts, the ECU is running. If you haven't (or can't) start the engine, observe the check engine light when you first turn on ignition. It should come on for five seconds and then go back out. If it stays on constantly, then suspect something related to the ECU and/or wiring leading up to it. In addition to the check engine light test, check to see that the in-dash stock boost gauge needle moves up to about the half-way mark and stays there when you turn the ignition key on.
By FAR, the best way to check your diagnostic cable is to try it in a known working car using a known working laptop. If the other person can connect to his ECU fine using his cable and then can't connect to his ECU using your cable, then it's a bad cable. If he can connect fine to his ECU using your cable, then you've got other issues in your car/laptop/wiring/ECU/whatever.