E. Fuel System Monitor

E1.) Fuel System Monitor - Information

The Fuel System Monitor is an on-board strategy designed to monitor the fuel trim system. The fuel control system uses fuel trim tables stored in the PCM's KAM to compensate for variability in fuel system components due to normal wear and aging. Fuel trim tables are based on vehicle speed and engine load. During closed loop vehicle operation, the fuel trim strategy learns the corrections needed to correct a "biased" rich or lean fuel system. The correction is stored in the fuel trim tables. The fuel trim has two means of adapting; a LONGFT and a SHRTFT. LONGFT relies on the fuel trim tables and SHRTFT refers to the desired air/fuel ratio parameter "LAMBSE". LAMBSE is calculated by the PCM from HO2S inputs and helps maintain a 14.7:1 air/fuel ratio during closed loop operation. SHRTFT and LONGFT work together. If the HO2S indicates the engine is running rich, the PCM will correct the rich condition by moving SHRTFT in the negative range (less fuel to correct for a rich combustion). If after a certain amount of time SHRTFT is still compensating for a rich condition, the PCM "learns" this and moves LONGFT into the negative range to compensate and allows SHRTFT to return to a value near 0%. Input from the ECT or CHT, IAT, and MAF sensors is required to activate the fuel trim system, which in turn activates the Fuel System Monitor. Once activated, the Fuel System Monitor looks for the fuel trim tables to reach the adaptive clip (adaptive limit) and LAMBSE to exceed a calibrated limit. The Fuel System Monitor will store the appropriate DTC when a fault is detected as described below.

^ The H025 detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating a rich or lean condition.

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

^ When deviation in the parameter LAMBSE increases, air/fuel control suffers and emissions increase. When LAMBSE exceeds a calibrated limit and the fuel trim table has clipped (reached adaptive limit), the Fuel System Monitor sets a DTC.

^ The MIL is activated after a fault is detected on two consecutive OBD II drive cycles.

The Fuel System Monitor DTCs can be categorized as follows:

^ Fuel Delivery Error - P0148

^ Lean shift in fuel system operation - P0171 (Bank 1) and P0174 (Bank 2)

^ Rich shift in fuel system operation - P0172 (Bank 1) and P0175 (Bank 2)








E2.) Fuel System Monitor - Diagnostic Trouble Codes