P0301 on Toyota: How to Diagnose & Fix
Cylinder 1 Misfire Detected
12 Toyota models · 18 documented issues · 7 critical · $50-$5,000 repair
P0301 on Toyota by model: symptoms, diagnosis and fix
Gen 3 and Gen 4 Prius models develop heavy carbon buildup in the EGR valve and intake manifold, causing rough idle, misfires, and reduced performance. The Atkinson-cycle engine's low combustion temperatures promote carbon accumulation in the EGR system.
Common Symptoms
- Rough idle
- Engine misfires at low RPM
- Check engine light with P0401 EGR code
- Reduced power
- Poor fuel economy
How to Fix
Clean or replace the EGR valve (Toyota 25620-37120 for 2010-2017). Clean the intake manifold ports of carbon buildup using walnut blasting or manual cleaning. Replace EGR pipe gaskets. Some owners install an EGR cooler bypass as a long-term fix. Clean every 60,000-80,000 miles as maintenance.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota 25620-37120 EGR valve
replace an EGR valve that remains electrically or mechanically faulty after full-system diagnosis and cleaning Fitment/availability: 2010-2015 Prius and Prius Plug-in 2ZR-FXE; also cataloged for Prius v, but not the issue's unsupported 2…
- Toyota 25627-37010 EGR-valve gasket
reseal the EGR valve joint after removal for verified cleaning or replacement Fitment/availability: 2010-2015 Prius 2ZR-FXE EGR-valve joint; confirm VIN and the joints disturbed during service Fitment/availability: Ships in 1-3 business …
- Toyota 25634-37030 EGR-pipe gasket
reseal the EGR pipe joint after removal for verified cleaning or replacement Fitment/availability: 2010-2015 Prius 2ZR-FXE, replacing 25634-37010; verify VIN and joint location Fitment/availability: Ships in 1-2 business days with Add to…
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Sources for this issue (3)
The 1.5L 1NZ-FXE engine can develop head gasket failure allowing coolant and oil mixing, often after overheating or prolonged coolant loss. Typically appears after 150,000+ miles. External coolant leaks may also occur at the head gasket mating surface.
Common Symptoms
- Coolant level dropping with no visible leak
- White smoke from exhaust
- Milky residue on oil filler cap
- Overheating
- Bubbles in coolant reservoir
How to Fix
Replace head gasket with Toyota OEM MLS gasket. Machine the cylinder head for flatness. Replace thermostat, water pump, and timing chain tensioner while engine is apart. Use Toyota Pink SLLC coolant.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota 04112-21213 1NZ-FXE engine valve-grind gasket kit
provide the exact upper-engine gasket set after head-gasket failure is confirmed and sealing surfaces are measured Fitment/availability: 2004-2009 Prius 1.5L 1NZ-FXE; supersedes 04112-21210/-21211/-21212 and still requires VIN confirmati…
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Sources for this issue (2)
The water pump on the 3.5L 2GR-FE fails prematurely between 80,000-120,000 miles, developing a coolant leak from the weep hole or gasket surface. If not addressed, complete pump failure causes overheating and potential head gasket damage.
Common Symptoms
- Coolant leak from front/center of engine
- Coolant level dropping
- Overheating at idle or low speeds
- Whining noise from water pump area
- Sweet coolant smell
How to Fix
Replace water pump (Toyota 16100-09442, which supersedes 16100-39455/16100-39456, or Aisin WPT-803). Replace the thermostat at the same time (confirm the 2GR-FE thermostat part number by VIN). Use Toyota SLLC or equivalent coolant. The pump is driven by the serpentine belt, so inspect the belt and tensioner during replacement.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Aisin WPT-803 mechanical water pump
confirmed mechanical pump leak or bearing-failure branch Fitment/availability: 2005-2018 Toyota Avalon 3.5L 2GR-FE mechanical water-pump application; confirm VIN and production date Fitment/availability: direct product page and cart cont…
- Genuine Toyota 90916-A3002 thermostat
thermostat branch when due, diagnosed or deliberately replaced during overlapping cooling-system service Fitment/availability: 2005-2018 Toyota Avalon 3.5L; replaces 90916-03133, 90916-03140 and 90916-A3001; confirm VIN Fitment/availabil…
- Toyota 00272-SLLC2 50/50 Super Long Life Coolant
correct coolant for refill and bleed after mechanical pump service Fitment/availability: Toyota Super Long Life Coolant maintenance/refill branch; verify total system quantity and never mix incompatible coolant Fitment/availability: Add …
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Sources for this issue (2)
The GR Corolla's 1.6L turbocharged three-cylinder G16E-GTS makes about 300 hp, which is high output for its size. The concern is that sustained high-boost use, such as track days or an aggressive tune, could make the factory head gasket seep coolant. This is not an established failure pattern. We found no Toyota service bulletin, recall or warranty extension for GR Corolla head gaskets, and no documented run of failures on stock cars. The evidence is indirect. Aftermarket makers sell reinforced head gaskets for this engine and market them for high-boost builds. Cometic's multi-layer steel gasket (C14201-035) is pitched for "high compression and turbocharged conditions" to "reduce blowout risks." HKS sells a grommet-type gasket for the G16E-GTS (listed for the GR Yaris, which uses the same engine). It is aimed at drag racing and time attack, and HKS says it still works when boost is raised further. Neither maker says the stock gasket fails. Treat this as something to watch on hard-driven or modified cars, not a known defect.
Common Symptoms
- Coolant level slowly dropping
- White residue near head gasket mating surface
- Slight coolant smell after hard driving
- Combustion gases in coolant (tested with block test kit)
How to Fix
Check first: with the engine cold, look at the coolant reservoir level before and after any track session or hard drive. A falling level with no visible drip is the trigger to investigate. Have a shop pressure-test the cooling system to rule out external leaks from hoses, the radiator, the water pump or the thermostat housing. Then have them run a combustion-gas (block) test on the coolant. Only a positive block test or visible seepage at the head-to-block joint points to the head gasket. Bulletin or recall: none found for this issue. Warranty: on an unmodified car, take confirmed seepage to a Toyota dealer and ask whether the powertrain warranty covers it. Expect them to ask about tuning or other modifications. For tuned or heavily tracked cars, aftermarket gaskets built for higher boost are available, such as the Cometic C14201-035 MLS and the HKS grommet type. They are performance upgrades, not a Toyota fix.
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 (2)
The 1.5L 1NZ-FE engine in the Echo develops oil leaks at the valve cover gasket and the oil filler cap seal. The rubber valve cover gasket hardens with age and heat cycling, allowing oil to seep down the side of the engine onto the exhaust manifold, producing a burning oil smell. The spark plug tube seals (integral to the valve cover gasket) also leak, allowing oil to pool around the spark plugs and cause misfires. The oil filler cap O-ring also dries out and leaks.
Common Symptoms
- Burning oil smell from engine bay
- Oil dripping down side of engine
- Oil pooling around spark plugs (misfires)
- Visible oil around valve cover edges
- Check engine light with misfire codes
How to Fix
Replace the valve cover gasket with a Toyota OEM gasket kit that includes spark plug tube seals. Clean all oil residue from the exhaust manifold after replacing. Replace the oil filler cap O-ring (or the entire cap for $10). Apply a thin bead of RTV sealant only at the cam cap corners where the valve cover gasket doesn't seal perfectly.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota 11213-21011 genuine cylinder-head-cover gasket
replace the molded valve-cover gasket after confirming leakage at the cover joint Fitment/availability: 2000-2005 Toyota Echo 1.5L 1NZ-FE; replaces 11213-21010; confirm VIN/current supersession Fitment/availability: Ships in 1-3 business…
- Toyota 90430-37140 genuine oil-filler-cap gasket
replace the cap seal when cleaned-and-rechecked evidence identifies seepage at the oil filler cap Fitment/availability: 2000-2005 Toyota Echo 1.5L 1NZ-FE; exact filler-cap gasket catalog fitment; confirm VIN/current supersession Fitment/…
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipThis is a 30-minute DIY job — just 4 bolts hold the valve cover on. Apply a tiny bead of RTV at the two front cam cap corners for a perfect seal.
- WarningDon't ignore oil pooling around spark plugs — oil-soaked ignition coils fail prematurely and cost $60+ each
The 2.4L 2TZ mid-mounted four-cylinder is prone to head gasket failure, and the risk climbs on the 1994-1997 supercharged 2TZ-FZE where added boost/heat accelerates wear. Failures cluster around 100,000-150,000 miles and are almost always triggered or worsened by the Previa's marginal, hard-to-service cooling system letting the engine overheat and warp the aluminum head (aluminum head on a cast-iron block expands faster and loses the seal when it overheats). Because the engine sits under the front seats, this is one of the most labor-intensive head gasket jobs of any 1990s vehicle, which is why owners treat cooling-system upkeep as head-gasket insurance.
Common Symptoms
- White smoke from exhaust
- Coolant loss with no visible external leak
- Overheating
- Engine misfire or rough running
- Bubbles/exhaust gas in coolant reservoir
- Milky oil
How to Fix
Address any overheating source first (thermostat, radiator, water pump, air pockets). Replace the head gasket with the OEM multi-layer steel gasket, resurface/pressure-test the head for warpage or cracks, and replace head bolts. Owners strongly recommend refreshing the entire cooling system at the same time given the labor to get in. On high-mileage vans a used/reman JDM 2TZ can be cheaper than the head-gasket labor.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Mizumo Auto MA-4216913516 Previa head-gasket set with bolts
head sealing and bolt set after head-gasket failure, repairable surfaces and cooling root cause are confirmed Fitment/availability: 1991-1995 naturally aspirated 2TZ-FE and 1994-1997 supercharged 2TZ-FZE Toyota Previa per the retailer; c…
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Sources for this issue (3)
P0301 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 P0301 mean on a Toyota?
P0301 stands for "Cylinder 1 Misfire Detected." P0301 means the engine computer detected a misfire specifically in cylinder 1 — the spark didn't ignite the fuel properly, or the fuel/air mix didn't burn as it should. The computer detects this by sensing tiny variations in crankshaft speed each time a cylinder fires. A misfire wastes fuel, raises emissions, and can damage the catalytic converter if it's severe or persistent (a flashing check engine light usually warns of active, converter-damaging misfires). Because the code points to one specific cylinder, the cause is usually an ignition, fuel, or compression problem isolated to that cylinder. On Toyota it is documented across 12 models: Prius, Avalon, GR Corolla, Echo, Previa, Corolla, Tacoma, Venza, Camry, Yaris, Highlander, 86.
What are the most common causes of P0301?
The most common causes of P0301 are: Worn or fouled spark plug in cylinder 1, Failed ignition coil or coil pack for cylinder 1, Faulty or clogged fuel injector for cylinder 1, Vacuum or intake air leak affecting that cylinder, Bad spark plug wire (on applicable engines), Low compression (worn rings, leaking or burnt valve, head gasket), Carbon buildup on intake valves, Wiring or connector fault to the coil or injector. The specific cause varies by vehicle.
How much does it cost to fix P0301 on a Toyota?
Published repair estimates on Toyota range from $50 to $5,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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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.