P0306 on Toyota: How to Diagnose & Fix
Cylinder 6 Misfire Detected
2 Toyota models · 3 documented issues · 2 critical · $100-$3,500 repair
P0306 on Toyota by model: symptoms, diagnosis and fix
Toyota/Subaru recalled early 2022-2023 GR86 and BRZ models for improperly manufactured valve springs in the FA24 engine. Defective springs can fracture, causing engine misfires, rough running, and potential engine stalling while driving. Recall 22V-879.
Common Symptoms
- Engine misfires
- Check engine light
- Rough idle or running
- Loss of power
- Engine stall while driving
How to Fix
This is covered under recall 22V-879 (Toyota) / WRJ-23 (Subaru). Contact Toyota dealer to check VIN eligibility. The repair involves replacing all 16 intake and exhaust valve springs at no cost. Do not ignore this recall - a fractured valve spring can cause catastrophic engine damage.
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Sources for this issue (1)
The first model years of the 4.0L 1GR-FE V6 used an early head gasket design whose sealing material between the cylinder and the coolant jacket degrades over time, allowing a small coolant leak into a cylinder. The classic signature is a cold-start misfire on cylinder 4 (and sometimes cylinder 6) that 'steam-cleans' the spark plug, throwing P0304/P0306, together with slow coolant loss from the reservoir (owners report topping off every few weeks) and a gurgling sound from the heater core on startup. Because the leak is small early on, it is frequently misdiagnosed as a bad coil or plug before the head gasket is identified. Left unaddressed it progresses to overheating and possible head/block damage.
Common Symptoms
- Cold-start misfire on cylinder 4 or 6
- Slowly disappearing coolant with no visible external leak
- Need to add coolant every few weeks
- Gurgling from heater core on startup
- Check Engine Light with P0304/P0306
- White exhaust vapor on cold start
- Eventual overheating
How to Fix
Diagnose with a cylinder leak-down/compression test, a combustion-gas (block) test of the coolant, and cooling-system pressure testing to confirm internal coolant loss before replacing parts. The repair is to remove the heads and replace both head gaskets with the updated/superseded gasket, resurface and inspect the heads, and refill with the correct coolant. Replace head bolts per spec if torque-to-yield. Verify no oil-in-coolant or coolant-in-oil contamination that would indicate further damage.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota 04112-0P061 genuine 1GR-FE valve-grind gasket kit
supply the coordinated top-end seals for a confirmed head-gasket repair after inspection and machine work Fitment/availability: 2005-2012 Toyota Tacoma 4.0L 1GR-FE top-end gasket kit; supersedes 04112-31080 and 04112-0P060, with VIN conf…
- Toyota 90910-02162 / 90910-A2006 genuine cylinder-head bolt
replace each head fastener that the factory procedure identifies as non-reusable or out of specification Fitment/availability: Individual 1GR-FE cylinder-head fastener application; 90910-02162 is superseded by 90910-A2006 and the repair …
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Sources for this issue (3)
P0303 indicates a misfire on cylinder 3. On the 3rd-gen Tacoma 3.5L 2GR-FKS V6, owners commonly trace this to a failed coil-on-plug ignition coil or spark plugs that are worn or past their ~60k-mile service window. Toyota has acknowledged coil-related P0301-P0306 misfires on its 2GR family and issued a technical service bulletin (L-SB-0044-19 / NHTSA MC-10169331) updating the older ignition coil part number (90919-02280) to a revised coil (90919-A2013). Off-brand spark plugs of the wrong heat range can also induce misfires on these engines even when new, because Toyota's ignition system is tuned to specific Denso/NGK plugs. The COP layout makes cylinder 3 easy to isolate by coil swap.
Common Symptoms
- Rough idle / vibration
- Flashing or steady check engine light
- Stumble or hesitation under load
- Reduced power and fuel economy
- Occasional hard start
How to Fix
Swap the cylinder 3 coil to an adjacent cylinder and re-scan; if the misfire follows, replace the coil (use the updated Toyota coil per TSB L-SB-0044-19 / MC-10169331 where applicable). Replace spark plugs as a set with OEM-spec Denso/NGK iridium plugs at the correct gap/heat range if they are worn or aftermarket. Verify the coil connector and check the injector/compression on cylinder 3 only if coil and plug are confirmed good.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Toyota 90919-A2008 genuine 2GR-FKS ignition coil
replace the cylinder 3 coil only when the misfire follows it or testing proves it failed Fitment/availability: 2016-2023 Tacoma 3.5L 2GR-FKS Type A ignition-coil branch; one per cylinder, six engine-wide, with VIN confirmation required F…
- Toyota 90919-01263 genuine FK20HBR8 iridium spark plug
replace a fouled or damaged cylinder 3 plug, or all six as a matched set when wear or service interval supports replacement Fitment/availability: 2016-2023 Tacoma 3.5L 2GR-FKS FK20HBR8 branch; six required for a complete set and VIN conf…
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Sources for this issue (4)
- Toyota TSB L-SB-0044-19 (NHTSA MC-10169331) — MIL ON with misfire DTCs P0301-P0306, ignition coil update 90919-02280 → 90919-A2013 (2GR engines)tsb
- Ignition coil problems — 3rd Generation Toyota Tacoma Forum (Tacoma3G)forum
- Still have P0303 code after plugs, wires and coil — Tacoma Forumforum
- P0303 Engine Code | Cylinder 3 Misfire Detected (Toyota Tacoma) — FIXDarticle
P0306 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 P0306 mean on a Toyota?
P0306 stands for "Cylinder 6 Misfire Detected." This code means the engine computer detected a misfire on cylinder 6 — that cylinder isn't burning its fuel-air mixture properly. The computer senses misfires by watching for tiny variations in crankshaft speed each time a cylinder should fire, and when cylinder 6 repeatedly fails to contribute, this code sets. You may feel a shake or stumble, especially at idle or under load, along with reduced power and possibly a flashing check-engine light, which signals a misfire severe enough to damage the catalytic converter. A misfire comes down to a problem with spark, fuel, or compression in that cylinder. On Toyota it is documented across 2 models: GR86, Tacoma.
What are the most common causes of P0306?
The most common causes of P0306 are: Worn or fouled spark plug on cylinder 6, Failed ignition coil for cylinder 6, Clogged, leaking, or failed fuel injector, Vacuum or intake air leak affecting that cylinder, Low compression (worn rings, burnt valve, head gasket), Damaged plug wire or coil connector, Carbon buildup or worn valvetrain components. The specific cause varies by vehicle.
How much does it cost to fix P0306 on a Toyota?
Published repair estimates on Toyota range from $100 to $3,500 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.
Looking for P0306 on a different make?
View P0306 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.