* Faulty Oil Pressure Relief Valve: This valve regulates oil pressure. If it's stuck open, it releases too much oil pressure, causing the light to illuminate even if there's sufficient oil. This is a likely culprit if there's no knocking. Knocking usually means low oil pressure damaging engine components.
* Worn Oil Pump: The oil pump is responsible for circulating the oil. If it's worn out or failing, it may not be generating sufficient pressure. This is more serious and requires repair or replacement.
* Clogged Oil Pick-Up Tube or Screen: The oil pick-up tube draws oil from the bottom of the oil pan. If the tube is clogged with sludge or the screen is blocked, the pump can't get enough oil.
* Low Oil Level (despite recent check): Even if you recently checked the oil, there might be other issues, such as a leak you haven't noticed or the oil level sensor isn't working correctly. Double check the level. A low level *can* trigger the light even if the pump is working.
* Wiring Issue (despite replacing sending unit): While unlikely after replacing the sending unit, there's a small chance of a wiring problem between the sending unit and the light itself, such as a short or loose connection.
* Gauge Issues (less likely): Though you replaced the sending unit, the gauge itself might be faulty, though this is less likely if the light is coming on and not just a gauge reading.
What to do next:
1. Verify Oil Level: Check your oil level again. Use a dipstick and ensure it's within the correct range.
2. Check for Leaks: Inspect the engine for any oil leaks. Look around the oil pan, filter, and seals.
3. Measure Oil Pressure (most important): The only definitive way to know if you have sufficient oil pressure is to use a mechanical oil pressure gauge. This gauge temporarily connects to the oil system and provides an accurate reading. This is crucial because your existing light is only an indicator, and not an accurate measurement tool. Auto parts stores often rent or loan these gauges.
4. Investigate Oil Pump and Relief Valve (if mechanical gauge shows low pressure): If the oil pressure is low, it's time to look at the oil pump and relief valve. This often requires professional attention. The pump might be a relatively inexpensive fix.
Caution: Continuing to drive with a potential oil pressure problem could severely damage your engine. It's best to avoid driving the car until you've diagnosed and fixed the issue.
