Check engine

CHECK FUEL PRESSURE AND FUEL FLOW
CHECK FOR VACUUM LEAKS
CHECK IT FOR TUNE UP

Fuel System Monitor
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 Keep Alive Random Access Memory (RAM) to compensate for variability in fuel system components due to normal wear and aging. 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 system has two means of adapting; a Long Term Fuel Trim and a Short Term Fuel Trim. Long Term relies on the fuel trim tables and Short Term refers to the desired air/fuel ratio parameter "LAMBSE". Both are described in greater detail in this section in Powertrain Control Software, Fuel Trim under Electronic Engine Control System, Powertrain Control Software. Input from the ECT, IAT, and MAF, MC-VAF 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 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 Heated Oxygen Sensor (HO2S) detects the presence of oxygen in the exhaust and provides the PCM with feedback indicating air/fuel ratio.
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 gets larger and larger, air/fuel control suffers and emissions increase. When LAMBSE exceeds a calibrated limit and the fuel trim 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.

The Fuel Trim DTCs are P0170 for Bank 1 and P0173 for Bank 2.
The MIL is activated after a fault is detected on two consecutive drive cycles.

The Misfire Detection Monitor is an on-board strategy designed to monitor engine misfire and identify the specific cylinder in which the misfire has occurred. Misfire is defined as lack of combustion in a cylinder due to absence of spark, poor fuel metering, poor compression, or any other cause. The Misfire Detection Monitor will be enabled only when certain base engine conditions are first satisfied. Input from the ECT, MC-VAF or MAF, CKP sensors, and Misfire Detection sensor on distributor ignition applications is required to enable the monitor.