What does it mean?
OBD II fault code P0520 is a generic code that is defined as “Engine oil pressure sensor/switch -circuit malfunction”, and is set when the PCM (Powertrain Control Module) detects either an actual low oil pressure condition, or a malfunction in the oil pressure switch and/or its control circuit. On most applications, the oil pressure switch is a simple pressure switch that is fed with a reference voltage by the PCM.
The pressure-sensing mechanism in the switch is in direct contact with the oil circulating through the engine, and since changes in oil pressure produce either a decrease or increase in the oil pressure switch’s resistance, the PCM is able to “convert” the changes in resistance into a reasonably accurate representation of the actual oil pressure at any given moment and engine speed.
In practice, the PCM in any given application is programmed to recognize a range of signal voltages (that roughly correspond to actual oil pressure(s)) that represent the acceptable oil pressure range for that application. Thus, when the PCM detects either an abnormally high or low signal voltage, that by extension could indicate an abnormal oil pressure, it will set code P0520, and illuminate a warning light.
Non-professional mechanics should also take note that some applications employ more than one oil pressure switch. As a rule, these applications use one sensor to indicate high, or normal, pressure conditions, and another to indicate low-pressure conditions. The two switches are NOT interchangeable, which is why they are always differentiated by color, or some other clearly identifiable characteristic.
Refer to the manual for the application to determine the number, location, appearance [of the oil pressure switches], and the operating principles of lubrication systems that use more than one oil pressure sensor/switch. NOTE: When code P0520 occurs on some applications, the PCM may set also set code P2105 – “Throttle Actuator Control System – Forced Engine Shutdown”, which means that the PCM has initiated a forced shutting down of the engine to protect the engine.
Be aware that when codes P0520 and P2105 appear together, it may not be possible to restart the engine until code P0520 has been resolved. The image below shows a much-simplified schematic of a typical oil pressure switch. Note however, that while this example is a simple ON-OFF switch, other designs employ oil pressure-driven potentiometers to supply a more accurate representation of the actual oil pressure in the lubrication system.
Refer to the manual for the application being worked on for detailed information on the location, and operating principles of the oil pressure switch on that application.