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.
To troubleshoot problems related to DTC P2178 OBDII, try this:
See Technical Service Bulletins (TSB).
Check the wiring harness and its connectors of the Oxygen Sensor and Mass Air Flow Sensor. Look for burnt, frayed wires or wires that are rubbing against other components. Also, make sure the connectors are not corroded. Repair or replace if necessary. After these repairs, clear the code.
If the code returns, test with a voltmeter the signal going from the MAF Sensor to the PCM. The sensor signal should increase as engine speed increases. Compare the data with the manufacturer's specifications. If you find some inconsistencies, replace the MAF Sensor.