P0520 on Toyota: How to Diagnose & Fix
Engine Oil Pressure Sensor/Switch Circuit Malfunction
2 Toyota models · 2 documented issues
P0520 on Toyota by model: symptoms, diagnosis and fix
Toyota bulletin T-SB-0104-21 / TSB010421 covers vehicles built with the A25A-FKS, A25A-FXS, M20A-FKS or M20A-FXS engines, which includes the Crown's 2.5-liter A25A-FXS hybrid engine, and is listed by NHTSA against the 2023 and 2024 Crown. Repeated short trips in extreme cold prevent the oil from reaching full temperature, so moisture from blow-by gas condenses and accumulates in the crankcase. The emulsified oil looks milky or coffee-coloured, deposits form under the oil filler cap, and when the moisture in the oil freezes the oil pressure may drop and trigger the low oil pressure warning. Owners frequently mistake the milky oil for a head gasket failure. The Hybrid MAX 2.4-liter T24A-FTS is a different engine family and is not named in this bulletin.
Common Symptoms
- Milky, tan or coffee-coloured engine oil
- White emulsion deposits on the oil filler cap and dipstick
- 'Oil Pressure Low' message on the multi-information display
- Check engine light with low oil pressure DTCs
- Occurs after repeated short trips in freezing temperatures
How to Fix
Toyota's bulletin directs technicians to first pressure-test the cooling system to rule out an actual internal coolant leak, which would take the vehicle outside the bulletin. If no coolant leak exists, the remedy is an engine oil and filter change, after which the technician idles the engine to 122F and confirms the low-oil-pressure warning and DTCs do not return; the bulletin contains no ECM calibration update. Owners in cold climates should also avoid a pattern of only very short drives and should follow the normal 10,000-mile/12-month oil interval or shorter under severe service. The bulletin lists the procedure as not applicable to warranty, so the oil change is normally an owner expense.
Sources for this issue (4)
- Toyota T-SB-0104-21 Rev2 - MIL ON With Low Oil Pressure DTCs P05202A/P052477 and Milky/Discolored Engine Oil in Freezing Temperatures (NHTSA-hosted PDF)tsb
- Toyota TSB TSB010421 / T-SB-0104-21 — Milky/Discolored Engine Oil, listed for 2024 Toyota Crowntsb
- [Updated] T-SB-0104-21 — MIL ON with Low Oil Pressure DTCs P05202A and/or P052477 and Milky/Discolored Engine Oil in Freezing Temperaturesforum
- New Oil Contamination TSB: Milky Oil, Cap deposits, DTC's & Low Oil Pressure — ToyotaNationforum
Toyota bulletin T-SB-0104-21 Rev2 covers 2018-2024 model year vehicles with the A25A-FKS/FXS or M20A-FKS/FXS engine families, and the December 2021/February 2024 revisions bring the Corolla Cross into scope. On repeated short trips in extreme cold, moisture from combustion blow-by gases condenses in the crankcase faster than the engine reaches the temperature needed to boil it off. The water emulsifies with the oil, producing a milky tan sludge visible on the oil cap and dipstick. When that moisture freezes it can block or restrict the oil pickup and pressure circuit, at which point the vehicle displays an Oil Pressure Low warning on the multi-information display and can set MIL-on codes P05202A (oil pressure sensor signal stuck in range) and/or P052477 (engine oil pressure too low, severe). Owners in northern climates who use the vehicle for short commutes are the exposed population. Important caveat from the bulletin itself: a genuine internal coolant leak produces the same milky oil appearance, so a cooling-system leak must be ruled out before blaming cold-weather condensation.
Common Symptoms
- Milky, tan or foamy residue on oil filler cap and dipstick
- Oil Pressure Low warning on multi-information display
- Check engine light in very cold weather
- Oil level appears to rise between changes
- Symptoms appear only after repeated short cold-weather trips
How to Fix
Diagnosis first, then the bulletin procedure. Have the dealer confirm there is no internal coolant leak (which on this engine family often traces to the flow shut-off/coolant bypass valve). If none, the condition is cold-weather moisture condensation: the remedy is an oil and filter change to remove the emulsified oil, followed by driving habits that let the engine reach full operating temperature - trips long enough to boil off condensate, at least 15-20 minutes of running. The bulletin lists this repair as not applicable to warranty, so expect to pay for the oil change unless the dealer finds a covered fault. Do not simply reset the warning and keep driving - genuine low oil pressure will damage bearings.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
Sources for this issue (4)
- Toyota T-SB-0104-21 Rev2 - Milky/Discolored Engine Oil, MIL ON with P05202A and/or P052477 (NHTSA-hosted, 2024 revision)tsb
- Toyota T-SB-0104-21 original issue, December 17 2021 (NHTSA-hosted)tsb
- 2024 Toyota Corolla Cross TSB list showing TSB010421 applied to this modeltsb
- [Updated] T-SB-0104-21 - MIL ON with Low Oil Pressure DTCs and Milky/Discolored Engine Oil in Freezing Temperatures - Toyota owner discussionforum
P0520 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0520 mean on a Toyota?
P0520 stands for "Engine Oil Pressure Sensor/Switch Circuit Malfunction." This code indicates a general electrical fault in the circuit for the engine oil pressure sensor or switch. The computer monitors this circuit to know your oil pressure, and it has detected a signal that is missing, shorted, or otherwise out of the expected electrical range. This is typically a wiring or sensor problem rather than an actual loss of oil pressure, but because oil pressure is critical to engine life, it should never be ignored until confirmed. If oil pressure truly is low, serious engine damage can result. On Toyota it is documented across 2 models: Crown, Corolla Cross.
What are the most common causes of P0520?
The most common causes of P0520 are: Faulty oil pressure sensor or switch, Damaged, corroded, or loose wiring/connector at the sensor, Open or short in the sensor circuit wiring, Poor ground connection, Low engine oil level or genuinely low oil pressure, Failed PCM/ECM (less common). The specific cause varies by vehicle.
How much does it cost to fix P0520 on a Toyota?
Repair costs vary widely with the root cause and Toyota model; each issue on this page carries its own estimate where one is published.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.