Fuel system monitor: Description

The fuel system diagnosis monitors the fuel delivery system for its ability to provide compliance with emission standards.

This diagnosis is continuously performed if enable 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 & one multiplicative term) are within a band.

Out of this band a failure is detected (if cumulated time out of band is above a threshold).

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.