OBD-II car diagnostic trouble codes beginning with P1 indicate an issue with the powertrain that is unique to the manufacturer. Car mechanics use an OBD-II reader to determine the cause of a problem in a vehicle. P1171 and P1191 for Ford and P1274 and P1191 for GM vehicles are examples.
If a Ford vehicle displays the P1171 error code, it means that the rotor sensor is faulty. If the vehicle displays P1191, it indicates an issue with the voltage of the key line.
For GM cars, P1274 indicates that the injection wiring is incorrect. P1191 means that there is a leak in the intake air duct.
As the codes are unique to the two manufacturers, a GM vehicle displaying the P1171 or a Ford displaying the P1274 error codes indicate different problems with the vehicles. P1171 in a GM vehicle indicates that the fuel system receives too much air and very little fuel.