System and method for performing evaporative leak diagnostics in a vehicle

A vehicle comprising:

• an engine;
• a fuel system having a fuel tank connected to a canister by an isolation valve, the canister connected to the engine;
• an electric machine;
• a diagnostic module having a change-over valve (COV), an orifice, a pressure sensor, and a pump, the module connecting the canister of the fuel system to atmosphere such that the orifice fluidly connects the canister to the pump, the COV fluidly connects the canister to atmosphere, and the pump fluidly connects the orifice to atmosphere;
• and
• a controller configured to:
• (i) measure a reference pressure across the orifice to provide a dynamically established threshold with the COV in a first position;
• (ii) command the isolation valve to a closed position and command the COV to a second position to isolate the fuel system;
• (iii) command the pump to place the fuel system in a low pressure state;
• (iv) measure a series of pressures in the fuel system;
• (v) provide a diagnostic code when at least one of the series of pressure measurements crosses the dynamically established threshold within a predetermined time;
• and (vi) provide a diagnostic code when a slope of the series of pressure measurements after another predetermined time indicates a future pressure measurement crossing the dynamically established threshold.

A vehicle comprising:

• a fuel system having a canister;
• a diagnostic module having an orifice, a pressure sensor, a changeover valve, and a pump, wherein the valve and the orifice selectively provide a vapor flow path between the canister and atmosphere;
• and
• a controller configured to, in response to comparing a series of pressure measurements from the fuel in a low pressure state to a variable reference pressure measured across the orifice, provide a code.