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P0520 on 2012-2024 Mazda SKYACTIV-G Engines: Oil Pressure Switch Circuit Fixes

On Mazda SKYACTIV engines, P0520 almost always means the oil pressure switch itself has failed, often leaking oil into its electrical connector. It's a simple circuit fault, not a sign of low oil pressure. Replacing the switch is a straightforward DIY fix, with the part costing between $20 and $60.

17 minutes to read 2012-2024 Mazda Multiple Models
Most Likely Cause
Faulty Engine Oil Pressure Switch
Difficulty
2/5
Est. Time
0.8 hrs
DIY Doable?
✅ Yes
Shop Labor
$75 – $160
Parts Price
$20 – $60
⚠️ Drivable, but... — You can drive the vehicle, but do so with caution. The main risk is that a faulty switch cannot warn you of a genuine low oil pressure problem, which could lead to severe engine damage. Address the issue promptly.
Key Takeaways
  • P0520 on a SKYACTIV-G engine is an electrical circuit code, not a low oil pressure warning.
  • The most likely cause is a faulty oil pressure switch that is leaking oil into its own connector.
  • This is a relatively easy and inexpensive DIY repair. The switch is located near the oil filter.
  • Always check the connector for oil first; this is a definitive sign of a failed switch.
  • Unlike many trouble codes, P0520 on these Mazdas typically does not turn on the Check Engine Light.
For Mazda SKYACTIV engines, the P0520 code specifically indicates an 'Oil Pressure Switch Circuit Problem'. The Powertrain Control Module (PCM) sets this code when it detects that the oil pressure switch remains in the 'off' state for five continuous seconds even though the engine is stopped. This points directly to an electrical fault in the switch's circuit, not necessarily a problem with the engine's actual oil pressure while running. A key detail for this specific Mazda fault is that it does not typically illuminate the Check Engine Light, but the code is stored in the PCM's memory.

What's Unique About the 2012-2024 Mazda Multiple Models

Unlike many other vehicles where a P0520 code could indicate serious mechanical oil pressure issues, on the Mazda SKYACTIV-G platform, it is almost exclusively an electrical circuit fault. The diagnostic logic is very specific, checking the switch's status when the engine is off. This means the troubleshooting process is much more direct and less alarming, typically leading to a simple, inexpensive component replacement rather than a complex mechanical diagnosis. The code is triggered by an open circuit condition, which is exactly what a leaking, internally failed switch presents to the PCM.

Generation note: This guide covers multiple generations of Mazda3, Mazda6, CX-3, CX-5, and other models equipped with SKYACTIV-G engines from 2012 to 2024. The location and function of the single-pin oil pressure switch are consistent across these generations, making the diagnosis and repair process very similar for all.

Symptoms You May Notice

  • Oil pressure warning light may illuminate intermittently or stay on.
  • No Check Engine Light (for the P0520:00 sub-code).
  • Visible oil leak from the oil pressure switch, often seeping into the electrical connector.
  • Stored P0520 code found during a scan, even with no other symptoms.
⚠️ Don't Waste Money on the Wrong Fix
  • Replacing the oil pump. The P0520 code on this platform is a circuit fault, not a pressure fault. Replacing mechanical parts like the oil pump will not resolve it.
  • Assuming low engine oil level is the direct cause. While you should always check your oil level, a low level would typically trigger a different code (like P0524) or a constant oil light while driving, not the specific P0520 circuit fault which is detected when the engine is off.
  • Using the wrong viscosity oil. While incorrect oil can affect pressure, it is not the root cause for the P0520 circuit-specific code.

Most Likely Causes

  1. Faulty Engine Oil Pressure Switch 🔴 High Probability The internal seal of the sensor can fail over time due to heat and vibration, allowing engine oil to seep past the diaphragm and into the electrical connector housing. This oil contamination creates an open circuit, which the PCM detects when the engine is off, triggering the P0520 code.
    How to confirm: Disconnect the electrical connector from the oil pressure switch. If oil is present inside the connector, the switch has failed internally and must be replaced. This is the most definitive confirmation. If the connector is dry, perform a continuity test between the switch's terminal and body ground; with the engine off, there should be continuity.
    Typical fix: Replace the engine oil pressure switch. The new part typically comes with thread sealant pre-applied. The job requires a deep socket (often 24mm) and access can be tight, sometimes requiring removal of the airbox.
    Est. part cost: $20-$60
  2. Damaged Wiring or Connector 🟡 Medium Probability The wiring is located on the engine block and is exposed to heat and vibration, which can cause insulation to become brittle or pins in the connector to become loose or corroded. Oil leaking from a failed switch can also saturate and degrade the connector's internal seal over time.
    How to confirm: Visually inspect the wiring harness and connector for cracks, corrosion, or pulled-out pins. Perform a continuity test with a multimeter between the switch connector and the PCM connector (specifically PCM terminal 1P on many SKYACTIV models).
    Typical fix: Repair the damaged section of the wiring harness or replace the connector pigtail. If the connector is oil-soaked, cleaning it with electrical contact cleaner is essential, but the switch itself should still be replaced as it is the source of the oil.
    Est. part cost: $10-$30

Rare But Worth Checking

  • Powertrain Control Module (PCM) Malfunction: This is extremely rare. All other possibilities, including the switch and wiring, must be exhaustively ruled out before considering the PCM as the cause.

Diagnosis Steps

  1. Verify the engine oil level and condition on the dipstick to rule out any basic issues. Top up if necessary.
  2. Scan for codes to confirm P0520:00 is present. Note that the CEL will likely be off.
  3. Visually inspect the oil pressure switch. On most SKYACTIV-G engines, it is located on the engine block, often below the intake manifold and near the oil filter housing. Access may require removing the air intake box.
  4. Disconnect the electrical connector from the switch. Check for oil inside the connector. If oil is present, the switch is faulty and needs replacement. This is the most common failure scenario.
  5. If the connector is dry, inspect it and the wiring harness for any visible damage, corrosion, or loose pins.
  6. If no visual faults are found, use a multimeter to check for continuity on the signal wire between the oil pressure switch connector (harness side) and the corresponding pin at the PCM (e.g., terminal 1P). An open circuit here indicates a wiring problem.
  7. If wiring is confirmed to be good and the connector is dry and clean, the fault lies with the oil pressure switch itself. Replace the switch.

Parts You'll Likely Need

  • Engine Oil Pressure Switch (OEM #PE01-18-501B) — This is the most common failure point for the P0520 code on SKYACTIV engines, typically failing by leaking oil into the electrical connector. The part number PE01-18-501B supersedes older versions PE01-18-501 and PE01-18-501A.
    Trusted brands: Mazda (OEM), Standard Motor Products, Beck/Arnley, Denso, Bosch
    OEM price range: $35-$50
    Aftermarket price range: $15-$35

Technical Service Bulletins (TSBs) & Recalls

  • While no specific TSB directly addresses P0520, related TSBs for other oil pressure codes like P0524 (e.g., 01-016/19, 01-004/21) confirm that Mazda's primary focus for oil pressure issues is often on oil contamination, the oil control valve (OCV), or the oil pump, none of which apply to the P0520 circuit fault. This reinforces that P0520 is an isolated electrical issue.

Platform-Specific Known Issues

  • Access Varies by Model: On models like the Mazda3, the switch is relatively easy to access after removing the engine cover and airbox. On the CX-5, access can be tighter due to the engine bay layout, but the process remains the same.

Mechanic-Grade Diagnostic Values

  • Oil Pressure Switch Continuity (Engine Off) — expected: Continuity should be present between the switch's single terminal pin (part-side) and the engine block (body ground).. Failure: No continuity (an open circuit) indicates a faulty switch.
  • Oil Pressure Switch Continuity (Bench Test with Air Pressure) — expected: With no pressure applied, there should be continuity between terminal A and the switch body. When specified air pressure (e.g., 5.8 psi) is applied, there should be no continuity.. Failure: If continuity does not change state when pressure is applied, the switch is faulty.

Scan Tool Commands That Help

  • Mazda M-MDS (or equivalent): KOEO Self Test — After replacing the part and clearing the DTC from memory, this self-test is performed with the Key On, Engine Off to confirm the repair and ensure the P0520:00 code does not immediately return.

Wiring & Ground Locations

  • PCM Terminal 1P — At the Powertrain Control Module (PCM) connector, typically in the engine bay.. This is the specific pin where the signal wire from the oil pressure switch terminates. It is the endpoint for checking the wiring harness for an open circuit.
  • G4 — Right side of engine compartment.. This is a primary engine bay ground point. Since the oil pressure switch grounds through the engine block, a poor engine ground connection at points like this could potentially cause intermittent circuit issues, though it is a very rare cause for this specific code.
  • G1 / G2 — Behind the left headlight assembly.. These are additional chassis ground points in the engine bay. Verifying major grounds are clean and tight is a good practice during any electrical diagnosis.

OEM Part Supersession History

  • PE01-18-501, PE01-18-501A → PE01-18-501B — Standard part revision and improvement by the manufacturer.

Model Year Variations Within This Range

  • 2012-2024: While the diagnostic logic for P0520 is consistent, the specific PCM pin for the oil pressure switch signal is 1P on SKYACTIV-G engines, whereas on some older non-SKYACTIV Mazda engines (like the MZR 1.6), it was 1AR. This is important if using wiring diagrams for diagnosis.

Diagnostic Flowchart

The P0520 code on SKYACTIV-G engines is typically an electrical circuit fault rather than a mechanical oil pressure failure. Start by checking the oil level and the physical state of the pressure switch connector.
→ Top up oil to the correct level and clear codes. If the code was not P0520:00, investigate mechanical issues or TSB 01-004/21 if the vehicle has the 2.5L Cylinder Deactivation system (8th VIN digit 'M').
Locate the oil pressure switch (near the oil filter housing/intake manifold). Disconnect the electrical connector. Is there engine oil inside the connector housing?
→ The internal seal of the sensor has failed, allowing oil to seep into the electronics. Replace the oil pressure switch (approx. $20-$60). Clean the harness connector thoroughly with electrical contact cleaner before reconnecting.
Inspect the wiring harness leading to the switch. Are there signs of heat damage, brittle insulation, or loose pins in the connector?
→ Repair the damaged section of the wiring harness or replace the connector pigtail. Ensure the harness is routed away from high-heat areas of the engine block.
With the engine off and the connector unplugged, use a multimeter to check for continuity between the switch terminal and the switch body (ground). Is there continuity?
→ The switch is faulty internally even without a visible leak. Replace the oil pressure switch using a 24mm deep socket. Ensure the new part has thread sealant applied.
Perform a continuity test on the signal wire between the switch harness connector and PCM terminal 1P. Is the circuit intact?
→ There is a break in the signal wire between the engine block and the PCM. Trace the harness to locate the break, often found near high-vibration mounting points.
→ If the wiring is good and the switch tests OK for continuity while off, the fault may be intermittent. Replace the oil pressure switch as a preventative measure, as heat-induced diaphragm failure is the high-probability cause for this Mazda platform.

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

  • Carbon Buildup on Intake Valves 🟠 Medium — Common on all direct-injection engines. Becomes noticeable after 80,000-120,000 miles, causing rough idle, hesitation, or reduced power.
  • Infotainment 'Ghost Touch' and Malfunctions 🟡 Low — Widespread on 2014-2021 models. The screen registers phantom touches, changes settings, or reboots. Caused by digitizer degradation. (Ref: Customer Service Program (CSP13) extends warranty for the CMU, but often not the screen itself.)
  • SKYACTIV-Drive Automatic Transmission Jerkiness 🟡 Low — A common characteristic complaint, especially at low speeds or when cold. The transmission can feel jerky or hesitant due to its design, which mimics a DCT with a quick-locking torque converter. (Ref: Multiple TSBs exist for specific shifting issues, often resolved with a TCM software update or, in some cases, addressing contamination. (e.g., TSB 05-001/21))
  • Cylinder Deactivation System Faults (2.5L) 🟠 Medium — On 2018+ models with cylinder deactivation (8th VIN digit 'M'), issues can cause CEL for codes like P0524/P055F due to oil contamination affecting the oil solenoid valve. (Ref: TSB 01-004/21 addresses this with a new oil solenoid valve, oil change, and PCM reprogram.)
  • Cracked Cylinder Head (2.5T Engine) 🔴 High — A serious issue affecting the 2.5L Turbo engine in models like the CX-5, CX-9, and Mazda6, leading to coolant leaks into the cylinders. (Ref: Mazda has issued service alerts (e.g., SA-011/23) and established a procedure for cylinder head replacement.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, a used part is never a smart choice. The failure mode is due to internal seal degradation from heat and time, and the part is inexpensive.

What to inspect on the donor part:

  • Not applicable, do not purchase this part used.

OEM-only on this vehicle (don't cheap out):

  • While not strictly 'OEM-only', using a new OEM part or one from a reputable OEM supplier is highly recommended for reliability.

Aftermarket brands forum-validated for this vehicle:

  • Denso
  • Bosch
  • Standard Motor Products (SMP)
  • Beck/Arnley

Brands owners have reported issues with on this vehicle:

  • Unbranded, low-cost sensors from online marketplaces have a high rate of premature failure and are best avoided.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

2016 Mazda3 GX — 67700 miles

Symptoms: A metallic rattle from the car, which was very loud and annoying while at idle and when pressing the gas pedal, was followed by the P0520 code.

What fixed it: The user was waiting for a mechanic appointment; however, they noted that clearing the P0520 code caused a P0421 code to appear immediately after.

Source hint: Reddit r/AskAMechanic thread '2016 Mazda3 GX 109,000kms, Loud rattle from car'

2017 Mazda 3 GT 2.5L Skyactiv — 71500 miles

Symptoms: The Oil Pressure light came on intermittently. After topping up oil, the light went off but returned the next morning.

What fixed it: Initial attempts including changing the oil, filter, and oil pressure sensor did not solve the problem as the light returned shortly after.

Source hint: Reddit r/mazda3

Mazda CX-5

Symptoms: Leaking oil pressure switch.

What fixed it: Replacement of the oil pressure switch.

Source hint: Mazda Forum - CX-5 Oil Pressure Switch Replacement

  • P0524 — Related oil pressure code mentioned in TSB 01-016/19 and 01-004/21; often associated with oil contamination or the cylinder deactivation solenoid rather than a simple circuit fault.
  • P055F — An oil pressure-related code that can appear alongside P0524 on 2018+ 2.5L models with cylinder deactivation due to oil solenoid valve issues.
  • P0421 — Observed by owners appearing immediately after clearing a P0520 code on SKYACTIV-G models.

Frequently Asked Questions

Why is my oil pressure light on even though my oil level is full and there is no Check Engine Light?
On SKYACTIV-G engines, the P0520:00 sub-code often triggers the oil pressure warning light without illuminating the Check Engine Light. This is frequently caused by an internal seal failure in the oil pressure switch, allowing oil to seep into the electrical connector and create an open circuit.
Does TSB 01-004/21 apply to my P0520 code on a 2.5L Mazda?
No. TSB 01-004/21 specifically addresses oil pressure codes P0524 and P055F related to the cylinder deactivation system and oil solenoid valve on 2018+ models. P0520 is considered an isolated electrical circuit fault of the pressure switch itself.
Where is the oil pressure switch located on a Mazda3 vs a CX-5?
On most SKYACTIV-G engines, the switch is on the engine block near the oil filter housing, often below the intake manifold. While the Mazda3 offers relatively easy access after removing the airbox, the CX-5 engine bay layout is tighter, though the replacement process is the same.
Can I just clean the oil out of the connector to fix the P0520 code?
While cleaning the connector with electrical contact cleaner is an essential step if it is oil-soaked, the oil pressure switch must be replaced. The presence of oil in the connector proves the switch's internal diaphragm has failed.
Is the P0520 code related to the 'Ghost Touch' infotainment issue or the jerky transmission I'm experiencing?
No. These are separate known issues for these Mazda models. P0520 is a specific engine electrical circuit fault, whereas 'Ghost Touch' is a digitizer failure (covered by CSP13) and transmission jerkiness is often a characteristic of the SKYACTIV-Drive design or addressed via TCM updates like TSB 05-001/21.
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Wrenchy
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Meet Wrenchy → Updated Jul 21, 2026

The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.

Year Coverage
This article covers the OBD-II Code P0520 (Deep Dive) for:
  • Mazda Multiple Models: 2012201320142015201620172018201920202021202220232024
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