The regulations do not require the OBD system to output fuel consumption information, and do not standardize the units and calculation methods of fuel consumption. Therefore, it is impossible to obtain fuel consumption information from the OBD system.
However, based on the control principle of the EFI system, the values of intake pressure or Intake Flow provided by the OBD system, short-term fuel correction, and long-term fuel correction can be used to estimate the fuel consumption with a certain accuracy, however, this method is only effective under closed-loop Fuel Control and ineffective under acceleration and other conditions.
For systems with continuous oxygen sensors, the signal of the oxygen sensor and the incoming traffic or pressure can also be used for calculation. No matter which method, the speed of the signal output by the OBD system cannot be completely accurate and real-time. It can only be an approximate result.