Methods and systems are provided for diagnosing an in-range error of a pressure sensor arranged downstream of a lift pump in a fuel system of a vehicle. In one example, a method may include performing feedback control of the lift pump based on output of the pressure sensor, monitoring the pressure sensor output for flattening during the application of the voltage pulses, and adjusting operation of the fuel system depending on whether the pressure sensor output flattens for at least a threshold duration, which is indicative of an in-range error. The method may further include dynamically learning a setpoint pressure of a pressure relief valve of the fuel system and a fuel vapor pressure within the fuel system by monitoring pressure sensor output while adjusting the duty cycle of voltage pulses applied to the lift pump.

Methods and systems are provided for indicating a presence or absence of a source of degradation stemming from one of an intake manifold, exhaust system, or engine of an engine system. In one example, a method comprises rotating the engine unfueled and indicating the source of degradation based on both an intake air flow and an exhaust flow, as compared to baseline intake air flow and baseline exhaust flow. In this way, a source of degradation may be pinpointed, which may increase a lifetime of a vehicle engine system, reduce undesired emissions, and which may increase customer satisfaction resulting from shorter time spent on diagnosing such a source of degradation.

A method for safely capturing an engine RPM threshold in a spark-ignition internal combustion engines which may exceed the maximum safe unloaded RPM for that engine. Typical engines having a safe RPM high speed redline when coupled to a load, and a reduced RPM redline when decoupled and unloaded, can be set to activate ancillary equipment at a high redline, engine loaded RPM by deriving and processing data from the engine at a low, unloaded reduced RPM speed. The method requires operator reference to an existing OEM or after-market tachometer which enables the user to set a low RPM reference point while the engine is unloaded and running at a slow RPM. Raw data from the latter variable RPM threshold selected by a user is safely captured while the engine is operating unloaded, and a higher RPM threshold is calculated and set from the raw data. The higher RPM threshold may exceed the maximum safe unloaded RPM for said engine.

In a limited-current type gas sensor which detects oxygen-containing gas contained in an exhaust gas of an internal combustion engine, the decomposition current value of water (H.sub.2O) may be detected, and existence of an abnormality of output characteristics of the sensor may be diagnosed based on its deviation from a reference decomposition current value of water corresponding to the concentration of water contained in the exhaust gas. A NOx sensor and a SOx sensor can also diagnose remarkable and minute abnormalities of output characteristics. In addition, the reference decomposition current value of water may be acquired based on the concentration of water detected by a separate humidity sensor or the decomposition current value of oxygen detected by the limited-current type gas sensor. The reference decomposition current value of water may be corrected based on a decomposition current value of oxygen detected during a fuel cut.

Systems and methods for diagnosing operation of a sensor of an exhaust system are presented. In one example, the systems and methods may diagnose operation of the sensor when an engine is combusting air and fuel. Further, operation of the sensor may be diagnosed when the engine is not combusting air and fuel so that vehicle occupants may not be disturbed by the diagnostic.

An abnormality diagnosis system of an air-fuel ratio sensor 40 or 41 provided in an exhaust passage of an internal combustion engine and generating a limit current corresponding to an air-fuel ratio, comprises a current detecting part 61 detecting an output current of the air-fuel ratio sensor and an applied voltage control device 60 controlling a voltage applied to the air-fuel ratio sensor. The abnormality diagnosis system applies a voltage inside a limit current region where a limit current is generated and a voltage outside the limit current region to the air-fuel ratio sensor when the air-fuel ratio of the exhaust gas circulating around the air-fuel ratio sensor is made a predetermined constant air-fuel ratio, and judges a type of abnormality occurring at the air-fuel ratio sensor based on an output current of the air-fuel ratio sensor detected by the current detecting part at this time.

Methods and systems are provided for calibrating a vehicle intake humidity sensor positioned in an intake manifold of an engine of the vehicle. In one example, a method is provided, comprising in response to shutdown of the engine, and further responsive to conditions being met for calibrating the intake humidity sensor, requesting a humidity estimate from one or more weather devices, and calibrating the intake humidity sensor based on at least a confidence level in the one or more weather devices. In this way, the intake humidity sensor may be regularly calibrated, under conditions where accurate and robust calibration may be achieved, and where regularly calibrating the intake humidity sensor may improve engine operation and increase fuel economy.

Methods and systems are provided for a diagnostic of a humidity sensor positioned in an intake of an engine and adjusting engine operation responsive to findings of the diagnostic. In one example, the method may include sealing a vehicle exhaust system of an engine, combusting fuel at cylinders of the engine while flowing gases through the engine in a first direction, and then, flowing the combusted exhaust gases through the engine in a reverse, second direction to the humidity sensor positioned in the intake. The method may further include indicating degradation of the humidity sensor based on the output of the humidity sensor while flowing gases in the first and second directions.

To quickly determine whether or not the propulsive force of a vehicle drive source is abnormal. The onboard control device pertaining to the present invention has a drive manipulated variable detection unit for detecting or estimating a drive manipulated variable manipulated by a driver in order to impart a propulsive force to a vehicle, a command value calculation unit for calculating a command value for a drive source of the vehicle on the basis of the drive manipulated variable, a propulsive force control unit for controlling the propulsive force of the drive source on the basis of the command value, operating state detection units for detecting or estimating the operating states of the drive source, a drive manipulation rate of change calculation unit for calculating the rate of change in drive manipulation, an operating state rate of change calculation unit for calculating the rate of change in the operating state, and an abnormality detection unit for detecting abnormalities in at least the drive source on the basis of the rate of change in drive manipulation and the rate of change in the operating state.

Methods and systems are provided for generating a predictive tachometer profile at a tachometer of a vehicle. An engine speed offset can be generated based on an engine acceleration and an accelerator pedal position rate. A predictive tachometer profile displayed at the tachometer can then be generated based on the engine speed offset and an actual engine speed.