DTC P2668: Fuel Indicator Light Command/Actual State Do Not Match: Description
WARNING: This page is about a different car, the 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The Fuel Indicator Light (FIL) is located within the Fuel Gage Select Switch. The FIL indicates which fuel system is utilized to operate the vehicle. The FIL illuminates for a few seconds at start up for a bulb check. The FIL remains illuminated while the vehicle is operating on gasoline. The PCM controls the FIL by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the controlled component. The PCM monitors the status of the driver. If the PCM detects an incorrect voltage for the commanded state of the driver, DTC P2668 sets.