Generator will not start and the controller display shows E01 immediately after a start attempt.

Safety first: Turn the generator to OFF/AUTO-OFF, disconnect the battery negative cable, and ensure utility power is present so the home is not relying on the generator. Allow the engine to cool completely before working near hot parts.

• Check oil level: Remove the service panel on the Ryobi standby generator enclosure. Pull the engine dipstick, wipe it, reinsert fully, then check the level. Add the manufacturer‑specified oil (usually 10W‑30 or as listed in the Ryobi manual) until it reaches the FULL mark. Do not overfill.
• Inspect for leaks: Look around the oil filter, drain plug, and crankcase gasket for fresh oil. Tighten the oil drain plug and oil filter by hand plus a small additional turn if they are seeping. Replace a damaged oil filter or gasket.
• Check the low‑oil pressure switch connection: Locate the low‑oil pressure switch on the engine block (usually near the oil filter). Ensure the single‑wire or two‑wire connector is fully seated and not corroded. Clean contacts with electrical contact cleaner and reconnect firmly.
• Test the switch (advanced DIY): With the battery still disconnected, unplug the low‑oil switch. Using a multimeter set to continuity, check the switch according to the Ryobi service manual (typically closed to ground with no pressure, open with pressure). If readings are out of spec, the switch is likely faulty and should be replaced.
• Reset and test: Reconnect the battery negative cable, clear the E01 code if the controller allows, then attempt a manual start from the control panel. If the code returns with correct oil level and no wiring issues, stop and contact a qualified generator technician to verify actual oil pressure with a mechanical gauge.