Theory Of Operation

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The fuel injectors spray a calibrated amount of fuel when energized. When the fuel injectors are new, this value is learned in the Powertrain Control Module (PCM). Over time, as fuel injectors age, the amount of fuel can vary (increase or decrease). The PCM will adjust the energizing time of the fuel injectors as needed to compensate for the drift in the fuel injector spray volume. There is a maximum amount of variance allowed for each fuel injector. The PCM monitors the amount of correction to the energizing time for each fuel injector. The energizing time is calculated during Decel Fuel Shut-Off (DFSO). The fuel injectors are monitored individually by energizing a single fuel injector during DFSO and monitoring for a calculated increase in engine speed. Based on this, the PCM will adjust the energizing time as needed. The PCM will fail a fuel injector if the energizing time exceeds the calibrated limit for a given fuel injector. This is performed for each fuel injector. While one injector is monitored at a time, multiple injectors may be monitored during a single DFSO.

It is possible for an engine issue such as contaminated fuel or a small leak in the intake air system can to cause a fuel injector calibration fault before other fuel or intake handling diagnostics will exceed a calibrated threshold and set a DTC.