In-range sensor fault diagnostic system and method

A method for diagnosing an in-range fault of a cylinder pressure sensor in an internal combustion engine, comprising:

• monitoring a pressure signal from an engine pressure sensor, which is indicative of a fluid pressure within a combustion chamber of the internal combustion engine;
• monitoring an engine timing signal from an engine timing sensor, which is indicative of a rotation of an output shaft of the internal combustion engine and also indicative of a position of a piston within at least one cylinder;
• receiving the pressure signal from the engine pressure sensor and the engine timing signal from the engine timing sensor in an electronic controller;
• analyzing the pressure signal and the engine timing signal using the electronic controller, to determine, for at least one combustion event in the combustion chamber:
• a theoretical polytropic constant,
• a measured polytropic constant, and
• a difference between the theoretical polytropic constant and the measured polytropic constant;
• and
• calculating an adjusted pressure signal, using the electronic controller, based on the pressure signal and the difference such that the adjusted pressure signal compensates for changes to an accuracy of the engine pressure sensor over time.

A method for diagnosing a fault in a cylinder pressure sensor, comprising:

• calculating a theoretical polytropic relation relative to a combustion event;
• determining a theoretical polytropic constant;
• using a cylinder pressure signal and a position signal of an engine piston within an engine bore to calculate an actual polytropic relation for the combustion event;
• determining a measured polytropic constant;
• comparing the theoretical polytropic constant with the measured polytropic constant to determine an adjustment value;
• and
• using the adjustment value to correct the cylinder pressure signal.