1.6.6.1 Monitoring Function - High Pressure System
High pressure system diagnosis: P302A/P302B, P302C/P302D,
Fuel mass plausibility check: P3283/P3285, P3284/P3286
For gasoline direct fuel injection, a high pressure fuel control system is needed for fuel preparation and metering. The low fuel pressure from the fuel pump module within the tank is increased by the high pressure fuel pump and adjusted to a desired set-point fuel pressure.
The high pressure fuel system consists of a common fuel rail for all high pressure piezo injection valves, a fuel rail pressure sensor, a high pressure fuel pump with a built-in fuel volume control valve, and an overpressure valve.
High pressure has to be adjusted to values between 5 MPa and 20 MPa, depending on the engine load and on the engine speed. Therefore, the fuel pressure in the rail is measured and controlled with the help of the fuel volume control valve. The pre-control, determined by the desired fuel-mass and the fuel pressure set-point value, calculates the driver-signal for the fuel volume control valve. This calculated driver-signal is additionally controlled by a closed loop control, using the measured fuel pressure and the desired set-point value as input.
The high pressure system diagnosis consists of a rationality test and, in principle, analyses the difference between the measured fuel pressure, the set-point fuel pressure, and the output of the pressure controller. When the adjustable limit is reached, the output of the long term fuel trim and the lambda controller is also taken into account.
The pressure deviation is defined as the difference between the set-point and the measured value. This means that a pressure higher than the set-point leads to a negative deviation, and vice versa.
A not adjustable fuel rail pressure (too high) is detected when the pressure deviation or the output of the pressure controller is below a calibrated (negative) threshold and one of the output values of the lambda control (lambda controller and long term fuel trim) is below a calibrated (negative) threshold. This means that the air fuel ratio tends to be too rich when left uncorrected. When these conditions are fulfilled for a calibrated period of time, a malfunction is detected and a maximum fault high pressure system fault is set.
A not adjustable fuel rail pressure (too low) is detected when the pressure deviation or the output of the pressure controller is above a calibrated threshold and one of the output values of the lambda control is above a calibrated threshold. This means that the air fuel ratio tends to be too lean when left uncorrected. When these conditions are fulfilled for a calibrated period of time, a malfunction is detected and a minimum fault high pressure system monitoring is set.
The fuel mass plausibility diagnosis monitors the high pressure sensor signal plausibility.
A too high pressure sensor signal is detected when the pressure deviation or the output of the pressure controller is below a calibrated (negative) threshold and one of the output values of the lambda control (lambda controller and long term fuel trim) is above a calibrated threshold. This means that the air fuel ratio tends to be too lean when left uncorrected. When these conditions are fulfilled for a calibrated period of time, a malfunction is detected and a maximum fault high pressure sensor monitoring is set.
A too low pressure sensor signal is detected when the pressure deviation or the output of the pressure controller is above a calibrated threshold and one of the output values of the lambda control (lambda controller and long term fuel trim) is below a (negative) calibrated threshold. This means that the air fuel ratio tends to be too rich when left uncorrected. When these conditions are fulfilled for a calibrated period of time, a malfunction is detected and a minimum fault high pressure sensor monitoring is set.