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

Safety first: Turn the generator to OFF, disconnect the battery negative cable, and ensure the unit cannot auto-start. Allow the engine to cool completely before working around the crankcase.

• Check oil level: Remove the side service panel on your WEN standby generator. Pull the dipstick, wipe it, reinsert fully, then check the level. Top up with the oil grade specified in your WEN manual (commonly SAE 5W‑30 or 10W‑30 for many WEN air‑cooled units) until it reaches the FULL mark. Do not overfill.
• Inspect for leaks: Look around the oil filter, drain plug, oil pan gasket, and crankcase cover for wet oil. Tighten the drain plug and oil filter by hand plus a small additional turn if they are seeping. Replace any damaged crush washer or filter seal.
• Reset and test: Reconnect the battery negative cable. Clear the E01 code if your controller supports reset (usually by pressing and holding the STOP/RESET button). Attempt a manual start. If the unit starts and runs normally, monitor for further leaks.
• Check low oil pressure switch: If oil level is correct and no leaks are found, locate the low oil pressure switch on the engine block (usually near the oil filter). Disconnect its wire and check continuity to ground with the engine off; it should show continuity (closed). If it reads open or is shorted all the time, replace the low oil pressure switch with a WEN‑compatible part.
• Inspect wiring: Trace the low‑oil switch wire back to the control board harness. Look for pinched, rubbed, or corroded connectors. Repair any damaged wiring and clean terminals.
• Do not bypass safety: Never permanently bypass the low‑oil switch. If the code persists after oil and switch checks, have a qualified technician test actual oil pressure with a mechanical gauge.