P0520
PowertrainEngine Oil Pressure Sensor/Switch Circuit
The ECU keeps an eye on the voltage coming back from the oil pressure sensor or switch, and it expects that signal to sit within a sensible window. When the reading drifts outside that range, goes dead, or jumps around in a way that doesn't make sense, the ECU logs P0520. For you, that means one of two things: either the sensor and its wiring have gone faulty and your oil pressure is actually fine, or the sensor is telling the truth and you've got a real pressure problem. Until you've checked which, treat it as serious.
ⓘ Information only. This page provides general educational information about fault code P0520. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0520 mean?
P0520 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Engine Oil Pressure Sensor/Switch Circuit.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, and quite often the red oil pressure lamp as well
- • Oil pressure gauge doing odd things, reading pinned high, dropping to zero, or flickering
- • Warning light that comes and goes, often when the oil is hot or at idle
- • Knocking or tapping from the top of the engine if the low pressure reading is genuine
- • Some cars drop into limp mode or cut power to protect the engine
- • Engine that won't restart or shuts itself down when paired with other oil-related codes
Possible causes
Causes commonly associated with P0520, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed oil pressure sensor or switch, the usual suspect. They corrode internally or the diaphragm gives up, especially on higher-mileage cars
- 2. Damaged or oil-soaked wiring at the connector. Oil weeps past a leaking sensor and tracks down into the plug, ruining the contacts
- 3. Low or filthy oil causing a genuine pressure drop. Always rule this out before condemning anything electrical
- 4. Short or open circuit in the harness between the sensor and the ECU, sometimes from chafing against the block
- 5. Clogged oil filter or thinned-out oil reducing real pressure, common when a service is badly overdue
- 6. Worn oil pump or a sticking pressure relief valve, the expensive end of the scale
- 7. Faulty ECU. Rare, and the last thing you should suspect
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull all the codes and read the live oil pressure data while the engine runs. A reading frozen at 0 or stuck at max almost always points at the sensor or its wiring rather than the pump
- 2. Check the oil level and condition on the dipstick. Low or sludgy oil can cause both real low pressure and a confused sensor signal, so sort this before going further
- 3. Get under the car and look at the sensor itself and its plug. If the connector is full of oil or the wiring is corroded or rubbed through, you've likely found it
- 4. Back-probe the sensor connector with a multimeter and compare voltage and resistance to the manufacturer's figures. A reading miles off spec or no signal at all confirms a sensor or wiring fault
- 5. Fit a mechanical oil pressure gauge in place of the sensor and measure actual pressure at idle and at around 2,000 rpm. If the mechanical gauge shows healthy pressure, the engine is fine and the sensor is lying
- 6. If the mechanical gauge confirms low pressure, stop driving and look at the filter, oil pump, and relief valve
Common questions about P0520
Can I keep driving with a P0520 showing? +
Not until you know whether it's the sensor or real low pressure, and that's the whole point. If the red oil lamp is off and the engine sounds normal, a short careful drive to a garage is reasonable. If the red lamp is lit or you can hear any knocking or tapping from the engine, stop and switch off. Running an engine with low oil pressure wrecks the bearings and camshafts in minutes, and that's a four-figure rebuild instead of a cheap sensor.
Will this code stop me passing the MOT? +
The code on its own isn't a direct fail, but if the engine warning light is lit when the car goes on the ramp, the tester has to record it and it can fail you on that basis. The red oil pressure lamp staying on is a separate concern the tester will note. Fix the cause, clear the light, and drive a few cycles to make sure it stays off before booking the test.
What's it going to cost to sort out? +
If it's just the sensor, the part is usually £15 to £60 and an independent garage will have it done for £60 to £150 all in. Where it sits under the intake manifold, labour pushes that toward £250 to £400. A main dealer will charge more again on labour. If the mechanical gauge proves the oil pump or relief valve has failed, you're looking at several hundred pounds and possibly into four figures depending on the engine. Get the cheap sensor and wiring checks done first so you're not paying for guesswork.
How do I tell whether it's the sensor or the actual oil pressure? +
A mechanical oil pressure gauge settles it, and it's the one test worth insisting on. Screw it in where the sensor lives and read the pressure at idle and around 2,000 rpm. Good pressure on the mechanical gauge means the sensor or its wiring is at fault and the engine is healthy. Low pressure on the mechanical gauge means it's real, and then the oil level, filter, and pump are what you chase. Before any of that, pull the dipstick. Cheap, instant, and low oil explains a surprising number of these codes.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →