Low fuel turns on an animation reminding you to pit before you run dry. It is enabled per device on that page's Effects tab, and configured once in Universal Low Fuel Settings, where you set the Low Fuel Colour and choose where the warning applies:

• Always Visible
• Low Fuel Warning Deactivated in Hotlap mode
• Low Fuel Warning Deactivated in Qualification
• Low Fuel Warning Deactivated in Hotlap and Qualification

Those exist because on a one lap run you already know you are light on fuel and do not need to be told. There is also a Low Fuel Acknowledge so you can dismiss the warning once you have seen it, and separate switches for Practice, Qualify and Hotlap. A wheel button can be set to the Low Fuel Alarm effect as well.

Engine start is a white needle sweep animation across your RPM and telemetry LEDs that signals the engine firing. It is available on telemetry LEDs, steering wheel buttons, button boxes, eyebrows and matrix flag boxes, each with its own on and off switch, and shares one Engine Start Colour and Engine Start Animation Duration across every device through Universal Engine Start Settings.