Patent ID: 7278405

Claim:
A fuel injection system for an internal combustion engine comprising: an accumulator storing therein fuel under a given pressure which is to be injected into an engine; a fuel pump working to pressurize and supply the fuel to said accumulator; a fuel injector working to inject the fuel in said accumulator into the engine; a fuel pressure sensor working to measure a pressure of the fuel in said accumulator to output a signal indicative thereof; a pressure-reducing valve working to drain the fuel from said accumulator to a fuel tank to decrease the pressure of the fuel in said accumulator; and a controller working to monitor the signal outputted from said fuel pressure sensor to control the pressure in said accumulator, said controller including a first diagnostic circuit and a second diagnostic circuit, the first diagnostic circuit working to diagnose said fuel pressure sensor, the second diagnostic circuit working to monitor a behavior of the pressure in said accumulator, as measured by said fuel pressure sensor when activating said pressure-reducing valve to diagnose said pressure-reducing valve, when a first condition in which the monitored behavior of the pressure in said accumulator is different from a behavior of the pressure in said accumulator, as expected when said pressure-reducing valve is operating properly, and a second condition in which said first diagnostic circuit has diagnosed that said fuel pressure sensor is operating properly are both met, said second diagnostic circuit determining that said pressure-reducing valve is failing in operation thereof; and wherein the second diagnostic circuit works to open said pressure-reducing valve upon turning off of an ignition switch of a vehicle in which the engine is mounted and diagnose whether said pressure-reducing valve is operating properly or not based on the behavior of the pressure in said accumulator arising from opening of said pressure-reducing valve and a result of diagnosis of said fuel pressure sensor made by the first diagnostic circuit.