Code P0521: oil pressure: sensor signal out of range

Original definition (SAE J2012): Engine Oil Pressure Sensor/Switch Circuit Range/Performance^[1][2][3]

• P0521Engine oil pressure sensor or switch circuit: range or performance outside what is expected.
• P0520Engine oil pressure sensor or switch circuit: malfunction.^[2][6][10]
• P0522Engine oil pressure sensor or switch circuit: low voltage.^[2][11]
• P0523Engine oil pressure sensor or switch circuit: high voltage.^[2][12]

1. 1Low oil level, through consumption or a leak: it is the first cause given by most sources and the first thing to check.^{[1][2][4][5][7]}
2. 2Faulty oil pressure sensor or switch. Autodoc Club puts it first; other sources place it after the oil level.^{[1][2][4][5][7][13]}
3. 3Degraded, contaminated or incorrect-viscosity oil, or oil with sludge.^{[1][2][4][5][7]}
4. 4Blocked oil filter, or one that is wrong for that engine.^{[1][2][4][13]}
5. 5Worn or faulty oil pump, or blocked passages and pump strainer.^{[1][2][4][5][7][13]}
6. 6Internal engine wear that lowers the pressure.^[1][4][5]
7. 7Sensor wiring or connectors damaged by heat, corroded or with excessive resistance in the signal, 5 V supply or earth circuit.^{[1][2][4][5][7]}
8. 8Faulty control unit or software problems: an uncommon cause.^[1][4]

• Oil pressure warning light on in the instrument cluster, although AutoDTCs notes that it may or may not come on. RACE explains that red indicates a pressure problem that means you must stop, and that a flashing light can point to an electrical or sensor fault as well as to irregular pressure.^[1][5][8]Oil warning light: faults that cause it
• Engine warning light on. If it flashes, TroubleCodes.net interprets it as a condition that can damage the engine.^[1][5][7]Engine warning light: faults that cause it
• Knocking or other engine noises, typical of genuinely low oil pressure; TroubleCodes.net also mentions abnormal valvetrain noise in some cases.^[1][5][7]Engine knock: faults that cause it
• Loss of power as an engine protection measure.^[1]Less power: faults that cause it
• Limp-home mode (reduced-performance mode).^[1]Limp mode: faults that cause it
• Difficulty starting.^[1]Hard to start: faults that cause it
• The engine may stall.^[4]Engine stalls: faults that cause it
• Abnormally high or low reading on the oil pressure gauge or cluster display.^[4]
• No other driving symptoms when the fault is only in the sensor, according to AutoDTCs; so you cannot deduce from how the car behaves that the sensor is the culprit.^[5]

1. 1First of all, check the oil level with the dipstick and the condition of the oil, and look for leaks under the engine. It is the cheapest check and the most likely cause.^[1][2][7][8]
2. 2Note how the fault presents itself. If the red oil warning light comes on, the engine warning light flashes or the engine makes abnormal noises, stop the engine and call for recovery: do not treat it as a simple sensor fault.^[4][7][8]
3. 3Read all the stored codes and the scan tool data: check whether the code is active with the engine warm and whether there are others from the same circuit (P0520, P0522 or P0523). As an example from one manufacturer, AutoDTCs describes a code that sets when the reading drops below the calibrated minimum at 1,250 rpm with the engine warm.^[1][5]
4. 4Check that the oil is of the viscosity the manufacturer specifies and that the filter is the correct one and properly fitted.^[2][7]
5. 5Do the test that settles it: fit a mechanical oil pressure gauge and compare the actual pressure with the manufacturer's figure, at idle and at around 3,000 rpm. If the pressure is good, the fault is in the sensor or the wiring; if it is low, there is a real lubrication problem (level, pump, wear) and the car must not be driven. TroubleCodes.net warns that a pressure that barely meets the minimum is a sign of engine wear, not of a faulty sensor.^[2][6][7]
6. 6Only if the actual pressure is correct, check the sensor wiring and connector (heat, deterioration, corrosion) and measure the resistance and voltage of the signal, 5 V and earth circuits. In the P0522, Autodoc Club gives 0.5 to 4.5 V as the normal range for the sensor signal.^[5][7][11]
7. 7Replace the sensor only when the actual pressure is correct and its readings are out of specification; then clear the code and check that it does not return.^[2][6][7]

• P0521 on Seat8
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• P0521 on BMW6
• P0521 on Citroën6
• P0521 on Nissan6
• P0521 on Peugeot6
• P0521 on Renault6
• P0521 on Audi5
• P0521 on Dacia5
• P0521 on Mazda5
• P0521 on Toyota5
• P0521 on Fiat4
• P0521 on Hyundai4
• P0521 on Kia4
• P0521 on Opel4