Methods and systems are provided for monitoring corking of a canister vent valve (CVS) in a fuel vapor line during diagnostics of an evaporative emissions control (EVAP) system of a vehicle. In one example, a method includes, after isolating the EVAP system from atmosphere, opening each bypass valve of one or more bypass valves of one or more fuel vapor canisters to couple the EVAP system to a fuel system of the vehicle, and opening a canister vent valve (CVS) responsive to an EVAP system pressure decreasing to a threshold EVAP system pressure.

Systems and methods are presented herein for detecting a degradation condition in a variable volume device of a fuel tank of a vehicle. In one example, the issues described above may be addressed by a diagnostic method for a vehicle with a valve and a fuel tank having a variable volume device internal to the tank, comprising: operating the fuel tank over a diurnal cycle; and differentiating between degradation of the fuel tank and the variable volume device based on a fuel tank pressure at a plurality of different valve conditions; and indicating the differentiated degradation.

A leakage diagnostic device diagnoses leakage of evaporated fuel in an evaporative fuel treatment device. The evaporative fuel treatment device purges evaporated fuel, which is generated in a fuel tank and adsorbed on a canister, to an intake passage. The leakage diagnostic device includes a vent valve that blocks a first atmospheric passage, which connects the canister with an atmospheric opening, and a pump that pressurizes and depressurizes a second atmospheric passage, which is a bypass passage of the first atmospheric passage. The malfunction diagnostic device diagnoses malfunction of the leakage diagnostic device based on an output value of a pressure sensor that detects pressure in a passage connected to the canister.

An evaporated fuel treatment apparatus includes: a canister; a purge passage; a purge pump provided in the purge passage; and an atmosphere passage communicating with the canister. A leakage diagnostic device includes: two bypass passages provided between the purge passage on the upstream side of the purge pump and the atmosphere passage; a reference orifice; two three-way valves; a pressure sensor; and an ECU. When operating the purge pump under a predetermined condition, the ECU controls the two three-way valves to set a mode in which atmospheric air is pressure-fed into an air intake passage through the reference orifice and the purge pump, and a mode in which vapors in the canister are pressure-fed into the air intake passage through the reference orifice and the purge pump, and determines leakage by comparing a reference pressure and a leakage pressure that are measured when these modes are set.

A method for operating an evaporative emissions control system for use with a fuel tank that stores and delivers fuel to an internal combustion engine is provided. A vent shut-off assembly is provided that selectively opens and closes at least one valve to provide overpressure and vacuum relief for the fuel tank. The vent shut-off assembly selectively vents to a purge canister. The at least one valve is closed whereby vapor is precluded from passing from the fuel tank to the purge canister. A purge event is performed wherein dedicated fresh air is drawn into the purge canister and delivered from the purge canister to the engine.

An evaporative fuel processing device for determining a leak of an evaporation piping system also determined pump abnormality by including a pump, a pressure sensor and an abnormality determiner, i.e., by pressuring/de-pressuring the system to a positive/negative value against an atmospheric pressure for leak determination, by detecting a pressure of the system, and by determining a leak hole in a normal leak determination mode based on an absolute value of the detected pressure reaching or not reaching a target value after pump operation and based on an assumption that the pump is normal. Specifically, after lapse of a determination time from a pump stop, the absolute value equal to or less than a normal leak determination threshold value is determined that a leak hole is present in the system. Further, the absolute value not reaching the target value even after pump operation triggers a pump abnormality determination mode.

A leakage detector for a fuel vapor treatment device includes a control unit. The control unit shifts a purge control valve and a shutoff valve to a first state with the purge control valve is an opened position and the shutoff valve in a closed position, and then shifts the purge control valve and the shutoff valve to a second state with the purge control valve is a closed position and the shutoff valve in a closed position. The control unit compares a first purge passage pressure acquired from the purge passage pressure detector when the purge control valve and the shutoff valve were shifted to the second state with a second purge passage pressure acquired from the purge passage pressure detector after a lapse of a first waiting time after being shifting to the second state. This comparison is used to determine leakage in the purge passage.

Methods and systems are provided for determining a source of degradation stemming from a vehicle fuel system during a refueling event. Specifically, in one example a method may include responsive to a refueling lock that enables access to a fuel tank of a fuel system being manually unlocked in order to add fuel to the fuel tank, monitoring a pressure in the fuel system and a fuel level in the fuel tank during refueling the fuel tank, and indicating degradation of the fuel system as a function of both the pressure and the fuel level. In this way, fuel system degradation may be pinpointed during a refueling event that is enabled via manual unlocking of the refueling lock.

The evaporative fuel processing system includes a fuel tank, a canister, a pump, a pressure detection unit, a temperature detection unit, and a leak diagnosis unit a leak diagnosis unit configured to diagnose leak in the diagnostic object based on a first pressure change which is a change in pressure detected by the pressure detection unit when the temperature in the diagnostic object changes, a second pressure change which is a change in pressure detected by the pressure detection unit when the inside of the diagnostic object is pressurized or depressurized by the pump, a detected temperature by the temperature detection unit, a first preparation information and a second preparation information.

An active dual purge system includes: an intake pipe, a compressor to compress air, a canister to collect an evaporation gas, a purge line extending from the canister to a front end of the compressor, a branch line branching off from the purge line and extending to a rear end of a throttle valve body, a purge pump installed in the purge line, a purge valve installed in the purge line, a vent valve installed in a vent line extending from the canister toward the atmosphere, a first sensor installed in the purge line, and a second sensor installed in the purge line, and a controller to perform different tests on the purge pump, the purge valve and the vent valve in different operating states, and diagnose whether at least one of the purge line, the branch line, or the vent line are abnormal using on-board diagnosis (OBD).