Fuel System Monitor

PURPOSE
The Fuel System Monitor is an on-board strategy designed to monitor the adaptive fuel control system, using adaptive fuel tables stored in Keep Alive Memory (KAM) to compensate for variability in fuel system components due to normal wear and aging.

OPERATION
During closed-loop vehicle operation, the adaptive fuel strategy learns the corrections needed to correct a "biased" rich or lean fuel system. The correction is stored in the adaptive tables. The fuel adaptive system has two means of adapting; a Long Term Fuel Trim (LONGFT) and a Short Term Fuel Trim (SHRTFT). LONGFT relies on the adaptive fuel tables and SHRTFT refers to the desired air/fuel ratio parameter "LAMBSE". Both are described in greater detail in EEC-V Software and Hardware / Software - PCM Related / Adaptive Strategy /Fuel Control. Input from the Engine Coolant Temperature (ECT), Intake Air Temperature (IAT), and Mass Air Flow (MAF) sensors is required to activate the adaptive fuel control system, which in turn activates the Fuel System Monitor. Once activated, the Fuel System Monitor looks for the adaptive tables to reach the adaptive clip and LAMBSE to exceed a calibrated limit. The Fuel System Monitor will store the appropriate DTC when a fault is detected.

DTCs and MIL Operation






1 The Heated Oxygen Sensor (HO2S) detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating air/fuel ratio.

2 A correction factor is added to the fuel injector pulse width calculation according to the Long and Short Term Fuel Trims as needed to compensate for variations in the fuel system.

3 When deviation in the parameter LAMBSE gets larger and larger air/fuel control suffers and emissions increase. When LAMBSE exceeds a calibrated limit and the adaptive fuel table has clipped, the Fuel System Monitor sets a Diagnostic Trouble Code (DTC) as follows:

The DTCs associated with the monitor detecting a lean shift in fuel system operation are DTCs P0171 and P0174.

The DTCs associated with the monitor detecting a rich shift in fuel system operation are DTCs P0172 and P0175.

4 The MIL is activated after a fault is detected on two consecutive drive cycles.