Final answer:
Several potential issues could lead to poor fuel economy without triggering DTCs, including a clogged air filter, malfunctioning oxygen sensor, worn-out spark plugs, and fuel injector problems. These problems hinder engine efficiency despite advancements in fuel efficiency in newer cars.
Step-by-step explanation:
The possible causes of poor fuel economy when no diagnostic trouble codes (DTCs) are present could be due to several factors, which can still have significant effects on efficiency:
A clogged air filter can impede airflow to the engine, making it work harder and less efficiently.
A malfunctioning oxygen sensor might not trigger a code immediately but can lead to an improper fuel-to-air ratio, causing the vehicle to use more fuel.
Worn-out spark plugs can misfire, leading to inefficient combustion and wasted fuel.
An issue with the fuel injectors, such as clogging or leaking, can affect the precision of the fuel delivery system, again reducing efficiency.
While cars are generally becoming more fuel efficient, factors such as these mechanical issues, or even environmental factors like cold weather, can impact the vehicle's fuel economy negatively.