ServiceNomad RV · Knowledge
Onan Generator Fault Code 14
Fault Code 14 on Onan RV generators indicates a low oil pressure shutdown. This fault is triggered when the generator's oil pressure sensor detects insufficient oil pressure during operation, causing the generator to shut down to prevent engine damage. Understanding what causes Fault 14 helps you determine whether the issue is actually low oil, a failed sensor, or a problem with the oil pump or lubrication system.
What Fault Code 14 Means
Onan generators have an oil pressure safety switch that monitors engine oil pressure. If pressure drops below the safe threshold (typically 4-6 PSI depending on model) for more than a few seconds, the generator control board assumes a lubrication failure and immediately shuts down the generator to prevent catastrophic engine damage. Fault Code 14 is stored in the controller and displayed on the control panel or remote start switch. This fault is a critical safety feature—running a generator with low oil pressure will quickly destroy the engine due to lack of lubrication on bearings, cylinder walls, and other moving parts. However, Fault 14 can also be triggered by a faulty oil pressure sensor, wiring issues, or even incorrect oil viscosity in extreme temperatures.
Actual Low Oil Pressure Causes
If the generator truly has low oil pressure, the most common causes are low oil level (due to consumption, leaks, or failure to check), a failing oil pump, or sludge/debris blocking oil passages. Onan generators consume some oil during normal operation, and if you don't check and top off regularly, the level can drop below the safe operating point. A technician will check the oil level (generator must be on level ground), inspect for external oil leaks, and verify oil quality (clean, proper viscosity, not contaminated with fuel). If oil level is adequate but pressure is still low, they'll test the oil pressure switch with a mechanical gauge to determine if pressure is actually low or if the switch is faulty. Low actual pressure usually indicates an oil pump problem, which requires generator teardown and repair.
Oil Pressure Switch and Sensor Faults
The oil pressure switch is a simple mechanical device that closes a circuit when oil pressure is adequate and opens when pressure is low. Over time, these switches can fail, stick, or become contaminated with carbon and sludge. A failed switch may indicate low pressure even when actual pressure is normal, triggering false Fault 14 shutdowns. A technician will remove the oil pressure switch and test it directly with compressed air or a manual pressure source. If the switch doesn't operate correctly at the specified pressure (typically 4-6 PSI), it needs replacement. They'll also inspect the wiring from the switch to the control board for damage, corrosion, or loose connections that could cause false fault signals.
Oil Viscosity and Cold Weather Issues
Using the wrong oil viscosity or operating the generator in very cold temperatures can cause temporary Fault 14 shutdowns. If the oil is too thick (high viscosity in cold weather), it may not flow quickly enough during startup, causing a momentary low-pressure condition that triggers the fault. This is especially common if you use straight-weight oil instead of multi-grade oil in cold climates. Onan recommends 15W-40 oil for most operating conditions and 5W-30 for extreme cold. A technician will verify you're using the correct oil type and may recommend switching to synthetic oil for better cold-weather performance. They'll also check that the oil is changed regularly—dirty or contaminated oil can sludge up and restrict flow, causing pressure issues.
⚠️ Safety Notes
- Never bypass or disconnect the oil pressure safety switch—this critical protection prevents engine destruction.
- If you suspect an actual oil pressure problem (not just a sensor fault), do not run the generator until the issue is resolved.
💡 Prevention Tips
- Check generator oil level before every use and top off as needed.
- Change generator oil and filter according to the maintenance schedule (typically every 100 hours or annually).
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