Rail pressure monitoring

The rail pressure is monitored during engine start and engine operation by way of setpoint/actual value comparison. The rail pressure sensor supplies the actual value to the DDE. The target value is calculated by the DDE depending on the operating status. If the DDE detects a discrepancy between the specified and actual level that is outside the permissible limits, a fault is saved in the fault memory.

An impermissible deviation of the rail pressure from the setpoint can be caused by the following:

• External leaks at components in the common rail system
• Flow regulating valve not opening
• Internal leaks in common rail system, e.g.
  • In the high-pressure pump (e.g. worn piston)
  • on rail pressure control valve (diverting too little or too much fuel into the return line)
  • At the fuel injectors (too much volume in the return flow)
• External influences such as defective fuel supply system, clogged fuel return system, air in fuel system