Method to Diagnose a Failure of a Piston Oil-Cooling-Jet Valve of an Engine by Oil Pressure Monitoring

The invention provides a method to diagnose a failure of an oil piston cooling jet (OPCJ) valve 21 of an internal combustion engine. The OPCJ valve is located in an auxiliary line 20 connecting an engine lubrication line 12 to at least an oil jet for squirting lubricating oil from the engine lubrication line towards a piston surface. The method provides for monitoring the pressure variation in the engine lubrication line due to a switching signal sent to the OPCJ valve. The pressure variation may be compared to a determined pressure target value, and the target value may be determined by one or more parameters of the lubricant in the engine lubrication line, such as pressure and temperature, or from an empirically determined map correlating the target value to one or more operating parameters. The pressure variation may be determined by a pressure sensor 18, and the diagnosis may be executed by a computer program stored on a data carrier 22 associated with an ECU connected to the pressure sensor.