Gen2 OBD2 app review

What does PID stand for? I've seen it many times but without any info on it. Sorry. I'm new and I'm trying to get as much info as I can before I buy scanners and cables to try and diagnose the problem I have with my '07 Prius.

 

Parameter ID, I believe.

 

Thank you

 

(How) did you forward this to the developer to correct?

How do the other scanner measure pump rpm (likely same PID) could help this lone polish soul.

 

For any PID, a scan tool has to know several things:

• The network address of the ECU that should be asked for the value
• The parameter ID to send to the ECU when asking (the ECU's response may include values for more than one parameter if they fit in the width of a response)
• The offset and width in bits of the value in question, in case it's just one of several values in the response
• The arithmetic that needs to be performed on the raw response value to get a displayable value in some recognizable measurement unit, and
• The name of the measurement unit you end up with after doing the right arithmetic.

I haven't tried out Car Scanner myself, but you can make some guesses about what might be wrong based on the exact behavior you see. Does it show a number for pump RPM that just never changes, no matter what the pump is doing? Then maybe the parameter ID or even ECU address is wrong, or the bitfield offset/width are pointing to the wrong place in the response.

Does it give a value that changes, but the changes don't seem to have anything to do with what the pump is doing? Again, then, maybe the wrong address or PID or bitfield.

Does it give a value that repeatably changes, and changes when you expect it to as the pump RPM changes, but seems like a bogus number for RPM? Then maybe the arithmetic formula is wrong (though this also could happen if the bitfield offset/width are wrong, picking up some but not all of the response value).

So, a bunch of details go into properly retrieving and displaying a PID. Toyota doesn't freely publish those details; they are built into Techstream, and the non-free scantool vendors can get the details from Toyota by paying a license fee.

Everybody building free alternatives has to laboriously reverse-engineer those details one way or another, which is hard, and easy to get wrong. Somewhere on PriusChat there's a big XLS spreadsheet with all the successfully-reverse-engineered gen 3 PID details, but last time I checked, these water pump PIDs weren't there, suggesting no one had succeeded yet, and that's probably why the Car Scanner dev hasn't got it either. If anybody does work out the details that are right, they can be passed along to the Car Scanner dev and should also get added to that spreadsheet so others can benefit.

 

In the app