The OBDII fault code P2178 means the car’s computer has found an excessively rich condition or too much fuel in the air/fuel ratio. The reason may be due to mechanical or electrical faults in the circuit. This code is set for engine bank 1, or the place where cylinder number 1 is located.
To monitor the amount of fuel injected into the engine, the PCM (Powertrain Control Module) uses the O2 Sensor (Oxygen Sensor). The value provided by this sensor is necessary to calculate the air/fuel mixture.