If a vehicle fails a Smog Check due to high HC and CO emissions and has a P0175 trouble code, what is the most likely cause?

The most likely cause of high hydrocarbon (HC) and carbon monoxide (CO) emissions in conjunction with a P0175 trouble code indicates that the engine is running rich, meaning it is getting too much fuel relative to the amount of air. A P0175 code specifically signifies that the fuel mixture is rich on bank 2 of the engine.

A dirty or faulty mass airflow (MAF) sensor can directly contribute to this issue. The MAF sensor measures the amount of air entering the engine, and if it is dirty or malfunctioning, it may provide inaccurate readings. As a result, the engine control module (ECM) may erroneously compensate by injecting more fuel into the combustion chamber. This leads to an excess of fuel compared to air, causing elevated HC and CO emissions and aligning with the P0175 code.

In contrast, a defective fuel pressure regulator could also potentially cause a rich condition, but the MAF sensor's role in measuring intake air and how it can impact fuel delivery makes it a more direct contributor to the readings observed. An exhaust leak might affect emissions, but it is less likely to specifically cause high HC and CO along with a P0175 code without other supporting issues. Lastly, worn spark plugs can lead