Fuel System Monitor

PURPOSE
The fuel system monitor is a self-test strategy within the Powertrain Control Module (PCM) that monitors the adaptive fuel table. The fuel control system uses the adaptive fuel table to compensate for normal variability of the fuel system components caused by wear or aging. During normal vehicle operation, if the fuel system appears "biased" lean or rich, the adaptive fuel table will shift the fuel delivery calculations to remove the bias.





OPERATION
As the fuel control and air metering components age or vary from nominal value, the adaptive fuel strategy learns corrections while in closed loop fuel. These corrections are stored in a table that is a function of engine speed and load. It is called "long term fuel trim." The table resides in Keep Alive Memory (KAM) and is used to correct fuel delivery while in open or closed loop. As the components continue to change and the table learns the corrections, some values in the table may reach the calibrated clip or limit. This means that the adaptive fuel table can no longer compensate for additional changes in the fuel system. Further changes in the fuel system will cause deviation in the closed loop fuel parameter, called "short term fuel trim." As this trim gets larger and larger, fuel/air control suffers and emissions increase and a fault code is stored.

Entry conditions for the fuel system test are that engine rpm is within calibrated limit, air mass into the engine is within a calibrated limit, engine is at operating temperature and closed loop. Idle and decelerations are excluded from fuel system testing.


Malfunction Indicator Lamp (MIL) and Diagnostic Trouble Codes (DTC's)
After the malfunction has been present for two drive cycles, the MIL will come on and a DTC is stored. The MIL is turned off after three consecutive drive cycles without the same malfunction being detected. The DTC will be erased from memory after 40 warm-up cycles without the malfunction being detected after the MIL is turned off. Another method of erasing the DTC is by initiating a PCM Reset.

COMPONENTS
The fuel control system uses the heated oxygen sensor. Other Electronic Engine Control-V (EEC-V) components that provide input to the adaptive fuel table are Intake Air Temperature (IAT), Engine Coolant Temperature (ECT), and Mass Air Flow (MAF). The HO2S senses the amount of oxygen in the exhaust and as a result, fuel will be adjusted rich/lean. The IAT and ECT sense ambient and engine coolant temperature. The MAF measures the mass flow rate of incoming air.