P0520 Engine Oil Pressure Sensor/Switch Circuit Malfunction

The P0520 trouble code means the engine control module (ECM/PCM) has detected a malfunction in the engine oil pressure sensor or oil pressure switch circuit.

This is a general oil-pressure circuit code. Unlike P0522, which specifically indicates a low electrical signal, or P0523, which indicates a high electrical signal, P0520 does not identify the exact electrical direction of the problem.

The important point is that P0520 does not automatically mean the engine has low oil pressure.

The fault may be caused by the oil pressure sensor itself, its wiring, connector, power or ground circuit, or a problem with the actual oil-pressure system that is causing the sensor to report an implausible condition.

Because engine oil pressure is critical to lubrication, however, a mechanical oil-pressure problem should always be ruled out when the symptoms or warning lights suggest one.

What does the oil pressure sensor do?

The engine oil pressure sensor or switch monitors pressure within the engine's lubrication system.

Depending on the vehicle, it may provide the ECM with a continuously changing electrical signal corresponding to oil pressure, or it may function as a pressure switch that changes state when pressure crosses a predetermined threshold.

The information can be used for:

• Engine protection

• Oil-pressure warning strategies

• Variable valve timing control

• Diagnostic monitoring

• Hydraulic engine systems

• Turbocharger protection on some applications

The exact design varies considerably between manufacturers.

Some vehicles have a relatively simple oil pressure switch, while others use an electronic pressure sensor that allows the ECM to monitor pressure over a much wider range.

What does “Circuit Malfunction” mean?

The word “Malfunction” makes P0520 broader than codes such as P0522 or P0523.

The ECM has detected that the oil pressure sensor/switch circuit is not behaving as expected, but the code itself does not tell you whether the problem is:

• Low voltage

• High voltage

• An open circuit

• A short circuit

• An implausible signal

• An intermittent electrical problem

• A defective sensor

• A genuine oil-pressure problem

This is why P0520 should be treated as a starting point for diagnosis, rather than a direct instruction to replace the oil pressure sensor.

Common causes of P0520

Faulty oil pressure sensor or switch

The sensor is one of the first components to inspect.

Age, heat, oil contamination, and internal electrical failure can cause the sensor to produce an incorrect signal.

A pressure switch can also become stuck internally or fail to change state correctly.

Damaged wiring

The wiring between the sensor and ECM can become damaged by heat, vibration, oil, or physical contact with other engine components.

A wire may be:

• Broken

• Chafed

• Melted

• Corroded

• Shorted to ground

• Shorted to voltage

• Internally damaged

Poor connector contact

A loose or corroded terminal can interrupt the sensor signal.

Oil pressure sensors are often installed directly into the engine, so their connectors can operate in a harsh environment.

Reference voltage problem

On pressure sensors that use a reference voltage, a problem with the reference circuit can affect the sensor output.

The fault may not be inside the pressure sensor itself.

Ground problem

A poor sensor ground can cause an incorrect signal and trigger a circuit malfunction.

Actual low oil pressure

This possibility should never be ignored.

A low oil level, worn oil pump, blocked oil pickup, excessive bearing clearance, or another lubrication-system problem can cause the oil pressure sensor to report an abnormal condition.

P0520 does not necessarily mean low oil pressure

This is one of the most important points when interpreting the code.

Imagine that the engine has perfectly normal oil pressure but the signal wire from the sensor is damaged.

The ECM may receive an abnormal signal and store P0520.

In this situation:

P0520 = yes

Actual oil pressure problem = no

Now consider an engine with a failing oil pump.

The sensor may correctly report an abnormal pressure condition, and the ECM can store P0520.

In that situation:

P0520 = yes

Actual oil pressure problem = yes

The code alone cannot distinguish these situations.

Symptoms of P0520

The symptoms vary depending on the vehicle and the cause of the fault.

Possible symptoms include:

• Check Engine Light

• Oil pressure warning light

• Oil pressure warning message

• Incorrect oil pressure displayed on the instrument cluster

• Engine protection mode

• Reduced engine performance

• Variable valve timing problems

• Rough running in some applications

• Ticking or tapping noises if actual oil pressure is low

• Engine noise that becomes worse as the engine warms up

Some vehicles may store P0520 without any noticeable drivability problem.

That is especially possible when the fault is limited to the electrical monitoring circuit.

What if the oil pressure warning light is on?

If P0520 is accompanied by a red oil pressure warning light, the situation should be treated more seriously.

Do not assume that the warning is caused by a defective sensor.

If actual oil pressure is too low, continued engine operation can cause severe damage to:

• Crankshaft bearings

• Connecting-rod bearings

• Camshafts

• Valve-train components

• Hydraulic tensioners

• Variable valve timing components

• Turbocharger bearings

If the warning remains illuminated while the engine is running, actual oil pressure should be verified as soon as possible.

Check the oil level first

Before concentrating on electrical diagnosis, check the engine oil level using the vehicle manufacturer's recommended procedure.

A low oil level can result from:

• External leaks

• Excessive oil consumption

• Damaged oil pan

• Oil filter leakage

• Drain plug leakage

• Turbocharger oil leakage

• Internal engine problems

If the oil level is low, it should be corrected with the correct oil specification.

But adding oil and clearing the code should not be considered a complete diagnosis if the engine has lost oil or the warning returns.

Oil quality and viscosity matter

Engine oil viscosity has a direct effect on lubrication-system behavior.

Using oil that is substantially thinner than the specified grade can affect pressure, particularly when the engine reaches operating temperature.

Using oil that is excessively thick can affect circulation during cold operation.

The correct oil should therefore meet the manufacturer's specified viscosity and performance requirements.

If P0520 appeared shortly after an oil change, the oil specification, level, filter, and installation should be checked carefully.

How P0520 should be diagnosed

A proper diagnosis begins with a complete scan of the ECM/PCM.

Do not immediately clear P0520.

First record:

• Stored codes

• Pending codes

• Freeze-frame data

• Engine RPM

• Coolant temperature

• Engine load

• Reported oil pressure, if available

Other codes can provide important clues.

For example, additional sensor voltage, communication, variable valve timing, or engine lubrication-related codes may help identify whether the problem is electrical or mechanical.

Inspect the oil pressure sensor and connector

The sensor should be inspected carefully.

Look for:

• Oil contamination

• Damaged connector

• Corrosion

• Loose terminals

• Bent pins

• Broken locking tabs

• Damaged insulation

• Wiring pulled tightly against the connector

Oil leaking around the sensor can also be significant.

A sensor that has developed an oil leak may need to be replaced even if the electrical fault is not immediately obvious.

Test the electrical circuit

The sensor circuit should be tested according to the vehicle manufacturer's wiring diagram.

Depending on the design, this may involve checking:

• Reference voltage

• Sensor ground

• Signal voltage

• Continuity

• Short-to-ground conditions

• Short-to-voltage conditions

• Connector terminal integrity

The correct test procedure depends on whether the vehicle uses a pressure sensor or a simple pressure switch.

Do not rely on a generic voltage value

There is no universal oil pressure sensor voltage that applies to every vehicle.

Different sensor designs use different electrical characteristics.

Likewise, the resistance of a pressure switch or sensor can vary depending on the design.

Therefore, the manufacturer's wiring diagram and technical specifications should be used instead of applying a generic internet-sourced voltage or resistance value.

Verify actual oil pressure

When there is any possibility that the engine genuinely has an oil-pressure problem, a mechanical oil-pressure gauge should be used.

This is one of the most important tests for P0520.

The technician can measure actual oil pressure and compare it with the pressure reported by the sensor or ECM.

If the mechanical pressure is normal but the electronic system reports an abnormal condition, the investigation can concentrate on:

• Sensor

• Switch

• Wiring

• Connector

• Reference circuit

• Ground

• ECM input

If the mechanical pressure is genuinely low, the problem moves into the engine's lubrication system.

What can cause genuinely low oil pressure?

If mechanical testing confirms low pressure, possible causes include:

Low oil level

Insufficient oil can prevent the pump from maintaining proper pressure.

Worn oil pump

An internally worn pump may not produce sufficient pressure, especially at hot idle.

Blocked oil pickup

Sludge, debris, or sealant can restrict the oil pickup screen.

Worn engine bearings

Excessive clearance allows oil to escape too easily, reducing system pressure.

Oil sludge

Heavy contamination can restrict oil passages and interfere with the lubrication system.

Pressure relief valve problem

A stuck or damaged pressure-regulating valve can affect oil pressure.

Incorrect oil viscosity

Oil that does not meet the manufacturer's requirements can affect pressure and oil flow.

Why hot-engine behavior is important

Oil pressure often changes significantly as engine temperature increases.

When oil becomes hot, its viscosity decreases.

An engine with marginal lubrication-system performance may therefore show a pattern such as:

Cold start → pressure appears normal

Engine reaches operating temperature → pressure falls

Hot idle → warning appears

This can point toward a mechanical problem such as oil pump wear or excessive bearing clearance.

However, a failing sensor can produce a similar pattern because the sensor itself is also affected by temperature.

That is another reason mechanical pressure measurement is so valuable.

Can P0520 be caused by an oil filter?

Potentially.

If the code appeared immediately after an oil and filter service, the following should be verified:

• Correct oil filter

• Correct filter installation

• Correct oil level

• Correct oil specification

• Oil filter condition

• Drain plug installation

• Any oil leaks

A severely restricted or incorrect filter can interfere with normal lubrication-system operation.

However, an oil filter should not automatically be blamed for P0520 without diagnostic evidence.

Can an oil pressure sensor leak oil?

Yes.

Depending on the sensor design, the component is exposed to engine oil internally.

A damaged sensor or its sealing area can develop an oil leak.

Oil contamination can also reach the electrical connector and potentially contribute to electrical problems.

If oil is present inside the connector, both the source of the leak and the electrical condition should be addressed.

P0520 on a turbocharged engine

P0520 deserves particular attention on turbocharged engines if there are signs of genuine low oil pressure.

Turbocharger bearings depend on proper oil lubrication.

If actual oil pressure is insufficient, turbocharger damage can occur.

Warning signs can include:

• Increased turbo noise

• Oil consumption

• Reduced boost

• Exhaust smoke

• Turbocharger shaft play

• Oil leakage

A turbocharged engine with P0520 and a red oil-pressure warning should not be operated until the lubrication system has been checked.

P0520 vs. P0521, P0522, P0523 and P0524

These codes are closely related but describe different conditions.

P0520 – Engine Oil Pressure Sensor/Switch Circuit Malfunction

General malfunction of the oil pressure monitoring circuit.

P0521 – Engine Oil Pressure Sensor/Switch Circuit Range/Performance

The signal is present but its value or behavior does not correspond correctly to expected conditions.

P0522 – Engine Oil Pressure Sensor/Switch Circuit Low Voltage

The electrical signal is below the expected threshold.

P0523 – Engine Oil Pressure Sensor/Switch Circuit High Voltage

The electrical signal is above the expected threshold.

P0524 – Engine Oil Pressure Too Low

The control system has detected a low engine oil-pressure condition.

The distinction between P0520 and P0524 is particularly important. P0520 primarily describes a problem with the monitoring circuit, while P0524 points more directly toward an insufficient oil-pressure condition.

A practical diagnostic example

Suppose a vehicle starts normally and the engine sounds completely normal.

The Check Engine Light comes on and P0520 is stored.

A scan tool shows an abnormal oil-pressure signal, but there is no oil-pressure warning light.

The technician checks the oil level and finds it correct.

A mechanical pressure gauge then shows that actual oil pressure is within the manufacturer's specification.

At this point, the engine does not appear to have a mechanical oil-pressure problem.

The investigation can move toward the oil pressure sensor, connector, wiring, reference voltage, ground, and ECM input.

Now consider a different vehicle where P0520 is accompanied by a red oil-pressure warning and engine ticking.

A mechanical pressure test confirms that oil pressure is below specification.

In this case, replacing the sensor would be the wrong first repair. The technician must investigate the oil pump, oil pickup, internal engine clearances, pressure-regulating system, and other mechanical causes.

What should be repaired?

The repair depends on the result of the diagnosis.

Possible repairs include:

• Replacing the oil pressure sensor

• Replacing the oil pressure switch

• Repairing damaged wiring

• Repairing a short circuit

• Repairing the sensor ground

• Repairing the reference-voltage circuit

• Repairing or replacing a damaged connector

• Correcting the oil level

• Correcting incorrect oil viscosity

• Replacing an incorrect oil filter

• Repairing the oil pump

• Cleaning a blocked oil pickup

• Repairing internal engine wear

The important point is that P0520 itself does not tell you which of these components has failed.

Final thoughts on P0520

P0520 Engine Oil Pressure Sensor/Switch Circuit Malfunction is a broad diagnostic code indicating that the ECM/PCM has detected an abnormality in the engine oil-pressure monitoring circuit.

It does not automatically mean that the oil pressure sensor is defective, and it does not necessarily mean that the engine has low oil pressure.

The correct diagnosis should separate two possibilities: an electrical monitoring problem and a genuine mechanical oil-pressure problem.

Checking the oil level, inspecting the sensor and connector, testing the electrical circuit, monitoring live data, and—when necessary—measuring actual oil pressure with a mechanical gauge are the most reliable ways to identify the cause.

If P0520 is accompanied by a red oil-pressure warning light, unusual engine noise, or other signs of lubrication failure, the issue should be treated as urgent until actual oil pressure has been verified.