What does it mean?
Despite the fact that the internal combustion engine is essentially the same as it was a century ago, in the ever-onward pursuit of better fuel economy and performance, automakers have discovered a number of ways to extract more power and fuel economy out of it. Direct fuel injection is nothing new, also having been invented more than a century ago.
Today, all diesel engines and many gasoline engines are taking advantage of the benefits of high-pressure fuel injection, directly into the cylinder on compression. Direct fuel injection delivers more power, better fuel economy, and lower emissions. On some modern cars, those equipped with high-pressure fuel injections systems, there are two fuel pumps. The low pressure (LP) pump is located in or near the fuel tank, while the high pressure (HP) pump is located on the engine.
The LP pump usually runs between 35 and 75 psi, which is used to feed port fuel injectors, if equipped, and the HP pump. The HP pump uses mechanical energy, usually from a camshaft, to ramp up fuel pressure to feed the direct fuel injectors. The HP fuel pressure can range from 500 to 5,000 psi, depending on application. Diesel engines may or may not use an LP pump, which may put out something like 5 to 15 psi. The HP pump ramps up fuel pressure as high as 23,000 psi, depending on application.
The ECM (engine control module) monitors fuel pressure for at least a couple of reasons. First, fuel pressure is important to modulate fuel injector pulse width. Generally speaking, higher fuel pressure requires less pulse width to get the same amount of fuel. Second, fuel pressure readings are used to modulate the fuel pressure regulator, which the ECM controls depending on driver demand and engine loading conditions.
Finally, fuel pressure needs to be finely controlled to keep from damaging anything. With HP fuel rail pressures ranging from 5,000 to 23,000 psi maximum, overpressure conditions could easily lead to component failure and leaks, such as from ruptured fuel lines or fittings. If the ECM detects a problem with the fuel rail pressure sensor (RPS), such as insufficient or excessive voltage feedback, or an open or short circuit, it will lock out the HP pump and put the engine into limp-home mode.
The MIL (malfunction indicator lamp) will be illuminated, and a DTC (diagnostic trouble code) will be set in ECM memory. DTC P0190 is defined as Fuel Rail Pressure Sensor Circuit Malfunction.