When using an OBD-II scanner, which specific sensor reading, when deviating significantly from its expected operating range under steady-state cruise, is the most direct indicator of a fuel consumption problem unrelated to mechanical friction or aerodynamics?

When using an OBD-II scanner, the specific sensor reading that is the most direct indicator of a fuel consumption problem unrelated to mechanical friction or aerodynamics, when deviating significantly from its expected operating range under steady-state cruise, is Long-Term Fuel Trim (LTFT). An OBD-II scanner is a diagnostic tool that connects to a vehicle's On-Board Diagnostics system to access real-time engine data, diagnostic trouble codes, and other information from the Engine Control Unit (ECU). Long-Term Fuel Trim, or LTFT, is a learned percentage adjustment the ECU applies to the base fuel injection pulse width over time. It represents the ECU's sustained effort to compensate for persistent deviations from the ideal air-fuel mixture, also known as the stoichiometric ratio. The stoichiometric ratio is the chemically ideal ratio of air to fuel for complete combustion, typically around 14.7 ....