OBDII Code Info
If your diagnostic connector looks like this one,then you have an OBDII sytem,and it requires a scanner to access the codes.Scanners can be found from the links on the homepage.All vehicles after 96 have the OBDII systems and some 95 models,too.
OBDII Code Definitions

OBDII P Codes

OBDII B Codes

OBDII C Codes

OBDII U Codes

Warning: These codes are GENERIC Please check for manufacturer specific codes with an appropriate manual

See the Scanner & Programs page for diagnostic options.
Be sure to double check the codes.
Codes may be Manufacturer specific and may not match the ones listed here.
Check specific manufacturer pages on the site, as some of them,
we list the OBD2 codes on those pages for those specific vehicles.

Pin 2 - J1850 Bus+
Pin 4 - Chassis Ground
Pin 5 - Signal Ground
Pin 6 - CAN High (J-2284)
Pin 7 - ISO 9141-2 K Line
Pin 10 - J1850 Bus
Pin 14 - CAN Low (J-2284)
Pin 15 - ISO 9141-2 L Line
Pin 16 - Battery Power

 Some 1995 GM vehicles have the 16-pin connector but have accessible OBD-I codes. Check the underhood emissions sticker to confirm, and if yours is OBD-I, the codes are accessed by bridging terminals 5 and 6. If your vehicle is OBD-II, a scan tool or computer is required to access the codes.
P 0 1 0 1
1  2 3 4 5

1st digit
P = powertrain
B = Body
C = Chassis

2nd digit
0 = Standard
1 = Manufacturer specific

3rd digit
1 = Emission management
2 = Injector circuit
3 = Ignition
4 = Auxiliary emission
5 = Vehicle speed & idle control
6 = Computer & output circuit
7 = Transmission

Note:OBD II oxygen sensor designation

For "V" engines; BANK 1 is always on the side of the engine with the number 1 cylinder (odd cylinders), and BANK 2 is always on the side of the engine where the number 2 cylinder (even cylinders) is located.