General Overview
The fuel system diagnosis shall monitor the fuel delivery system for its ability to provide compliance with emission standards.
This diagnosis is continuously performed if entry conditions are fulfilled.
The fuel system diagnosis checks if the sum of short-term fuel trim (only based on upstream sensor voltage monitoring) and long term fuel trim (one additive and one multiplicative term) are within a band.
Out of this band a failure is detected.
Different fuel system problems may occur:
- Fuel pressure problem: short term fuel trim deviation which induces emissions problem, but no effect on the catalyst window set point because of homogenous mixture, in steady engine conditions.
- Cylinder misdistribution problem due to injector failure: short-term fuel trim deviation with effect on the catalyst window set point because non-homogeneous mixture.