fault code guide
P0520: Engine Oil Pressure Sensor / Switch Circuit Malfunction
Fault code P0520 means the engine computer has detected an electrical fault in the oil pressure sensor circuit. You must pull over safely and check your oil immediately, as running an engine without proper oil pressure will ruin it.
How it shows up: You will usually see the amber engine management light, and on some cars the red oil pressure warning light or an oil gauge reading zero. The P0520 code itself will be confirmed using an OBD scanner plugged into the diagnostic port.
Updated 9 November 2026
Can I keep driving?
Stop driving
Stop driving immediately until you verify oil levels, because if the engine truly has low oil pressure rather than just a broken sensor, running it will cause catastrophic internal failure.
What to do right now
- 1Pull over as soon as it is safe to do so and switch off the engine immediately.
- 2Listen for any loud ticking, tapping, or metallic knocking sounds from under the bonnet before you cut the ignition.
- 3Leave the car parked on level ground for ten minutes so the engine oil can settle before inspecting anything.
- 4Call roadside assistance if the red oil warning light illuminated alongside the engine light.
Likely causes
Most likely first.
- Likely
Failed oil pressure sensor
The internal diaphragm or electrical switch inside the sensor breaks down from years of heat cycles and vibration, sending an impossible voltage signal to the engine computer.
- Possible
Corroded or loose electrical connector
Road dirt, water ingress, or leaking oil can get past the weather seal into the sensor plug, breaking the electrical circuit or shorting the pins.
- Possible
Damaged sensor wiring harness
The wiring loom running near hot exhaust components or moving belts can chafe through its protective sleeve, creating an open circuit or grounding against the engine block.
- Rare
Severely contaminated or incorrect engine oil
Heavy sludge or using the wrong oil viscosity can block the tiny intake orifice of the pressure switch, preventing the sensor from registering normal circuit transitions.
What you can check yourself
Park somewhere safe and level, engine off, before you start.
- 1
Check the engine oil level
Wait ten minutes after parking on flat ground, pull the dipstick, wipe it clean on a cloth, reinsert it fully, and pull it again. If the level is below the minimum mark, top up with the correct specification oil before restarting.
- 2
Look under the car for fresh oil puddles
Check the ground directly beneath the engine for wet patches. A sudden, massive oil leak can drop pressure rapidly and trigger switch circuit errors.
- 3
Inspect the sensor body and plug
Find the oil pressure sensor on the engine block or filter housing using your handbook. Ensure the plastic plug is clipped tight and that oil is not leaking out through the electrical pins.
- 4
Inspect visible wiring
Trace the thin wiring harness from the sensor back towards the main loom. Look for cracked insulation, melted sections touching the exhaust, or wires snapped by road debris.
Rough cost to fix
Rough estimateTypical prices in Ireland (€) and the UK (£), from an independent garage up to a main dealer. The total cost varies depending on how easily the mechanic can reach the sensor, as some engines require removing the intake manifold or alternator to access it.
Replace engine oil pressure sensor
- Do it yourself
- €25–80£20–70 in the UK
- At a garage
- €110–240£95–210 in the UK
Repair sensor wiring connector or loom
- Do it yourself
- €15–45£12–40 in the UK
- At a garage
- €90–200£80–180 in the UK
Engine oil flush, oil change, and filter replacement
- Do it yourself
- €50–120£45–105 in the UK
- At a garage
- €130–260£110–230 in the UK
When to go to a garage
- The red oil pressure warning light stays illuminated or flashes while the engine is running.
- You hear loud metallic tapping, clicking, or grinding sounds coming from the engine.
- The oil dipstick reads completely dry even after adding a litre of fresh oil.
- You replace the sensor yourself but the fault code returns immediately upon starting.
Questions drivers ask
Can I drive my car with fault code P0520 showing?
You should not drive until you have confirmed your oil level is correct and your engine sounds completely normal. Even though P0520 specifically refers to an electrical circuit fault, you cannot know for certain whether the engine has actual oil pressure without a mechanical gauge test. Driving with no oil pressure will destroy the engine bearings in seconds.
Will my car pass the NCT or MOT with code P0520?
In the UK, an active engine management light on the dashboard is an automatic MOT fail for petrol cars first used from July 2003 and diesels from July 2008. On the Irish NCT, an engine warning light or an OBD code alone yields an Advisory Pass under current rules, provided tailpipe emissions remain within legal limits. However, if the red oil warning light is illuminated, any tester will abort the test immediately.
Will clearing the P0520 code fix the problem?
No, clearing the code with a scanner only wipes the computer memory temporarily. As soon as the engine control module runs its diagnostic check and fails to see the expected voltage return from the sensor, the fault code and warning light will return. The underlying electrical fault or broken switch must be physically repaired.
How does P0520 differ from P0521, P0522, and P0523?
P0520 is a general circuit malfunction where the engine computer detects an open circuit or erratic signal. Codes P0522 and P0523 specify that the circuit voltage is stuck permanently too low or too high, respectively. Code P0521 indicates a range or performance problem, meaning the sensor is communicating but the pressure value does not match what the engine expects for its current speed.
Test rules here are for the National Car Test in Ireland (NCT) and the MOT in the UK. Elsewhere, check the regulations of your own country or state before going for a vehicle test.
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General guidance for most cars, not a diagnosis of yours. Details differ by make, model and year - check your handbook, and if in doubt, don't drive.