Disclosed is a method for diagnosing sealing in a fuel vapor recirculation system for an engine of a motor vehicle. An electronic module is integrated into the engine control unit that is woken up and placed on standby periodically while the engine is off, at the start and end of time intervals in order to perform a respective leak diagnosis, the fuel vapor temperature Tsys being estimated as a function of a time t ending at the start of each interval and starting when the engine is switched off according to the following equation, in which Tamb is the ambient temperature measured, Tsys0 is the fuel vapor temperature when the vehicle is switched off, and tsys is a system response time:
Tsys(t)=Tamb+(Tsys0−Tamb)e.sup.−t/tsys.

A method and a device for diagnosing a ventilation line of a motor vehicle are provided. The ventilation line is arranged between a fuel tank and an activated carbon filter. The motor vehicle has a control unit (ECU) and is powered by an internal combustion engine. The state of a vacuum switch is evaluated for the diagnosis.

Methods and systems are provided for diagnosing a restriction of a fuel vapor canister. In one example, a method may include diagnosing restriction of a canister filter responsive to a first rate of decay of pressure of the canister to a target pressure being less than a first threshold rate of decay, when evacuating the canister to the atmosphere, and a second rate of decay of a pressure of the evaporative emissions control system to a target pressure being greater than a second threshold rate of decay, when evacuating the canister to a fuel tank.

Methods and systems are provided for diagnosing degradation in a variable volume device included within a pressure-less fuel tank. In one example, a method may include, upon conditions being met, operating a pump of an evaporative emissions control (EVAP) system leak detection module (ELCM) to evacuate the variable volume device. A degradation of the variable volume device may be indicated based on a change in pressure at the variable volume device.

An evaporated fuel processing device that includes a pressurizing pump configured to pressurize gas in the vapor passage downstream of the closing valve toward the closing valve; a first pressure sensor configured to detect a pressure in the fuel tank directly or indirectly, and/or a second pressure sensor configured to detect a pressure in the vapor passage downstream of the closing valve directly or indirectly. When the closing valve moves toward an open side in the closed state with the pressurizing pump pressurizing the gas in the vapor passage downstream of the closing valve toward the closing valve, the controller may specify a valve-opening-start position based on the pressure detected by the first pressure sensor and/or the pressure detected by the second pressure sensor, wherein the valve-opening-start position is a position where the closing valve transitions from the closed state to the opened state.

A failure diagnostic device is configured to determine saturated vapor pressures of a fuel within a fuel tank. In a fuel vapor processing apparatus, some or all of the passages and spaces into which the fuel vapor flows into the fuel vapor processing apparatus are closed to the atmosphere. In this condition, the failure diagnostic device determines a plurality of saturated vapor pressure characteristics over time. The failure diagnostic device is configured to diagnose whether or not a leakage or a blockage failure in the fuel vapor processing apparatus is present. The failure diagnostic device determines a Reid vapor pressure (RVP) based on each of the plurality of determined saturated fuel vapor pressure characteristic and diagnoses whether or not a failure is present in accordance with a change in these RVPs over time.

A leakage detector for a fuel vapor treatment device includes a fuel vapor treatment device that maintains the interior of a treatment system of the fuel vapor treatment device in a sealed state. In addition, the leakage detector includes; a closing valve and shutoff valve that can shut off fluid communication between the fuel tank and the canister to section the interior of the treatment system into a first region including the fuel tank and a second region including the canister. Further, the leakage detector includes an aspirator that applies a negative pressure to the second region. The leakage detector for the fuel vapor treatment device determines the presence and/or absence of leakage in the first region on the basis of a change in the pressure in the first region while an engine is stopped and determines the presence and/or absence of leakage in the second region on the basis of a change in the pressure in the second region by applying a negative pressure to the second region while the engine is operated.

Methods and systems for performing diagnostics on an evaporative emission are described. The methods and systems may include evaluating pressure or vacuum development within an evaporative emissions system over time to determine the presence or absence of a breach in the evaporative emissions system. If a breach is identified, mitigating actions may be performed.

In a fuel tank system, a control unit diagnoses a failure of a fuel storage unit and a processing unit. The fuel storage unit includes a vapor passage through which a fuel tank and a sealing valve are communicated with each other, a first pressure detection unit, and a second pressure detection unit disposed at a position different from the first pressure detection unit. The control unit specifies a presence or an absence of a clogging of the vapor passage based on a first pressure value detected by the first pressure detection unit and a second pressure value detected by the second pressure detection unit when the pressure in the fuel tank is changed by the pressure generation unit in a condition that the sealing valve is controlled to be opened.

A leakage diagnosis device for an evaporative fuel treatment device includes a first vent valve, a second vent valve, and a pump. The first vent valve is configured to block a first atmospheric passage, which is a main passage of an atmospheric passage and connects a canister with an atmospheric opening. The second vent valve is configured to block a second atmospheric passage, which is a bypass passage of the first atmospheric passage and connects the canister with the atmospheric opening. The pump is provided on a side of the atmospheric opening relative to the second vent valve in the second atmospheric passage, and is configured to pressurize or depressurize the second atmospheric passage. A malfunction diagnosis device performs a malfunction diagnosis based on an output value of a pressure sensor, a current value of the pump, or an output value of an air-fuel ratio sensor.