I have to look it up..but here is the general format of OBDII codes.
They are usually 5 alphanumeric codes.
First one is always one of the following:
B = Body
C = Chassis
P = Powertrain
U = Network
Second is a numeric of 0 (zero) or 1 (one)...
0- SAE (standard)
1- manufacturer (additional code put in by perticular manufacturer)
Third is the most imporant digit.. 1-8
1- Fuel and Air Metering
2- Fuel and Air Metering (in fuel injection system only)
3- Ignition
4- Aux emission control
5- Idle control/ aux inputs
6- Computer/aux output
7- transmission
8- transmission
The last two digits always come together.... These digits are the pintpoint code. It tells what exactly is wrong.
In your case.. the full code would be P0173 - We know its fuel/air system. The 73 part, I have to look it up.