AutoZone in California will now let you use the scan tool yourself to pull
the codes. And they let you use the tool for free.

I'd like to explore the enhanced (P1 and P2, etc.) codes. The lists that I
have seen seem to show that while all codes are not always used, most codes
that are used always mean the same thing. That is, all cars won't produce a
P1234 (ficticious code that I pulled out of my a.s), but when a car does
produce a P1234, then it normally means the same for all cars that produce a
P1234. I do not argue that the codes are enhanced, I conpletely agree that
they are. But my very limited experience is that codes are uniform with a
few exceptions.

Got this from a class I was in recently, thought it was interesting.

How to basically read OBDll Standardized Diagnostic Trouble codes.

The codes start with a letter:

The trouble code area:
P- Powertrain
B- Body
C- Chassis
U- Network Fault

Who created this code:
0- SAE defined code
1- Manufacture defined code
2- Manufacture (they ran out of codes for 1 so they expanded to "2")

System:
0- Total system
1- Air-fuel control
2- Air-fuel control
3- Ignition system or misfire
4- Auxiliary Emission Controls
5- Idle or speed controls
6- Computer system (PCM or I/O)
7- Transmission
8- Non-computer controlled Powertrain

The last two digits indicate the specific problem area

So the code P1711 would tell us:

P- Powertrain
1- It's a manufacture's code
7- Transmission
11- Transmission oil temperature circuit out of range

and the code P0300 would tell us:

P- Powertrain
O- It's a SAE mandated code
3- Ignition system or misfire
00- random misfire detected