P0521: OBD-II code P0521 flags an implausible oil pressure sensor signal — the value doesn't correlate with engine RPM and oil temperature as expected.

Symptoms

• Check engine light is on; the oil pressure gauge may read erratically or jump around.
• On some vehicles, the low oil pressure warning may flash on and off unpredictably.
• No immediate engine damage — but a real low-pressure event could be masked by the bad sensor.

Common causes

• A failed oil pressure sensor drifting outside spec after years of exposure to hot oil and thermal cycling.
• Damaged wiring or a corroded connector at the sensor, common near the engine block.
• Genuinely low oil pressure from a worn pump or excessive engine wear — rule this out with a mechanical gauge first!

What to do?

Verify real oil pressure with a mechanical gauge FIRST — if actual pressure is low, do not drive the vehicle. If real pressure is normal, replace the electronic oil pressure sensor. Inspect the connector for damage during replacement.