P0520 on Toyota: How to Diagnose & Fix
Engine Oil Pressure Sensor/Switch Circuit Malfunction
3 Toyota models · 3 documented issues · 1 critical
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 water content freezes the oil pickup can be restricted enough to drop indicated oil pressure. 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 plus an ECM calibration update that raises engine operating temperature and improves crankcase ventilation warm-up under cold, short-trip conditions. 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. Covered under the 5-year/60,000-mile powertrain warranty when the vehicle qualifies.
Sources for this issue (3)
- 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's inspection and repair are covered under Toyota's 5 year/60,000 mile powertrain warranty when the DTCs are present. Do not simply reset the warning and keep driving - genuine low oil pressure will damage bearings.
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
Toyota says moisture from blow-by gases may condense and accumulate in the A25A-FXS engine oil during short trips in extreme cold weather. The oil may appear milky or discolored; if the moisture freezes, oil pressure may drop and the Oil Pressure Low warning or MIL may appear with P05202A and/or P052477. This exact bulletin condition is not evidence of the previous card's gasoline-dilution defect, damaging fuel-percent threshold or permanent thicker-oil remedy.
Common Symptoms
- Milky or discolored engine oil after short trips in extreme cold
- Oil Pressure Low warning on the multi-information display
- MIL illuminated with P05202A and/or P052477
How to Fix
Treat an Oil Pressure Low warning as a stop-and-diagnose condition. For milky/discolored oil, Toyota first requires inspection and a cooling-system pressure check; any internal coolant leak takes the vehicle outside this bulletin and must be diagnosed separately. If the cooling system holds pressure, a technician follows T-SB-0104-21 Rev2's DTC/warning gate, hybrid maintenance-mode warm-up checks and specified oil-and-filter procedure. Use the oil grade on the under-hood label and applicable manual; do not use a highway drive, owner-UOA threshold or permanent 0W-20 substitution as a repair.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Mobil 1 Advanced Fuel Economy full-synthetic 0W-16 motor oil, 5 qt
replace moisture-contaminated oil after the bulletin's coolant-leak and warning/DTC gates Fitment/availability: Five-quart container covers the bulletin's 4.8-quart A25 service quantity; use only where the under-hood label/repair manual …
- Toyota 90915-YZZN1 genuine oil filter
complete the bulletin oil-and-filter service Fitment/availability: Exact service filter named by T-SB-0104-21 Rev2 for the covered A25 engine procedure; confirm product number and pack size at checkout Fitment/availability: Add to Cart a…
- Toyota 90430-12031 oil-pan drain-plug gasket
reseal the drain plug during the bulletin oil service Fitment/availability: Exact single-use drain gasket specified by T-SB-0104-21 Rev2; confirm cart quantity and applicable repair-manual torque Fitment/availability: Ships in 1-3 busine…
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Sources for this issue (2)
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 3 models: Crown, Corolla Cross, RAV4.
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.
Looking for P0520 on a different make?
View P0520 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.