P0305 on Honda: How to Diagnose & Fix
Cylinder 5 Misfire Detected
3 Honda models · 6 documented issues · 3 critical · $120-$8,000 repair
P0305 on Honda by model: symptoms, diagnosis and fix
Owners of the 2006-2010 Ridgeline's 3.5L J35 V6 have reported spark plugs that loosened and blew out of the aluminum cylinder head while driving. One 2007 owner reported that at 67,442 miles, on the highway at 70 mph, "the spark plug blew out of the engine head in two pieces" and took the ignition coil with it. They said no check engine light came on first, and they were quoted $12,048.85 for the repairs. In another 2007 report, at 124,000 miles, the engine made an abnormal noise at about 55 mph. A technician then found that a spark plug had fractured and fallen into the engine, and the engine had to be replaced. Honda's specified spark plug torque for this engine is 18 N·m (13 lb-ft). We found no Honda service bulletin or recall for this problem.
Common Symptoms
- Misfire codes P0300-P0306 and a check engine light
- Rough idle or hesitation
- Abnormal engine noise while driving
- A plug and its ignition coil are blown out of the cylinder head while driving, sometimes with no warning light beforehand
- Damaged ignition coil after a plug blows out
- Severe engine damage if a broken plug falls into the cylinder
How to Fix
If you get a misfire code (P0300-P0306), the engine runs rough, or you hear a new noise from the engine, have the spark plugs checked before you drive hard again. Remove each ignition coil and check whether any plug is loose. If a plug is loose and the threads are still good, tighten it to Honda's spec of 18 N·m (13 lb-ft) with a torque wrench, not to 18 lb-ft. Use the same torque wrench and spec whenever you replace the plugs. If a plug has already blown out or broken, have a shop inspect the threads in the cylinder head and check the cylinder for pieces of the plug before the engine is run again. We found no recall, bulletin or warranty extension that covers this problem.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Honda / NGK 9807B-5517W IZFR5K11 spark plug, quantity oneOEMHonda 9807B-5517W / NGK IZFR5K11
exact early spark-plug replacement after inspection confirms plug replacement is due or required Fitment/availability: 2006-2008 U.S.
- Genuine Honda / NGK 12290-R70-A01 ILZKR7B11 spark plug, quantity oneOEMHonda 12290-R70-A01 / NGK ILZKR7B11
exact later spark-plug replacement after inspection confirms plug replacement is due or required Fitment/availability: 2009-2010 U.S.
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
- TipUse torque wrench when installing spark plugs - do not over-tighten (18 ft-lbs spec exactly)
- TipAlways work on engine when completely cool - aluminum expands significantly when hot and causes incorrect torque readings
- TipCheck spark plug torque at 60,000 miles and every 30,000 miles thereafter as preventive maintenance
- WarningHave coil packs inspected immediately if misfire codes appear - replacing coils early prevents catastrophic $4,000+ engine damage
Sources for this issue (4)
The 2006-2014 Ridgeline's J35A9 uses a belt-driven cam system with a hydraulic (oil-filled) timing belt tensioner rather than a spring tensioner. The tensioner seal weeps, the damper loses its charge, and belt tension goes slack. Ridgeline Owners Club threads report technicians finding a large share of high-mileage tensioners leaking. A slack belt lets the belt jump a tooth on a cam sprocket - first showing up as a random misfire under load - and if it skips far enough or shears, the J35 is an interference design and bends valves. The water pump is driven off the same belt and is a common co-failure, so a leaking tensioner discovered late often means the whole front of the engine.
Common Symptoms
- Oil weeping from the hydraulic timing belt tensioner / lower timing cover
- Rattle or slap from the timing belt area on cold start
- Random misfire under load
- Check engine light
- Rough running or no-start after belt skip
How to Fix
Replace the timing belt as a complete job at or before 105,000 miles / 7 years, and always replace the hydraulic tensioner, tensioner pulley, idler pulley, water pump, drive belt and cam/crank seals at the same time - never belt-only. Inspect the lower timing cover for oil residue at every oil change; wet residue at the tensioner is a leak, not a drip from above. Dealer pricing for belt + tensioner + water pump has run roughly $900-$1,700; a skipped belt on this interference engine runs $4,000-$5,000+ in valve, head and piston work.
Sources for this issue (3)
The PCM software may misinterpret sensor inputs as a deteriorated catalytic converter, and debris from the high-pressure pump or the injector machining process can cause internal wear or clogging inside one or more fuel injectors. P0420/P0430, P0300-P0306 and P219A/P219B may be stored. 2016-2017 Pilot (bulletin 20-100, with software update) and 2017-2019 Pilot (bulletin 21-010, without software update), all trims, eligibility by VIN.
How to Fix
Have a Honda dealer verify the VIN and stored codes against 20-100 (2016–2017 Pilot, with software update) or 21-010 (2017–2019, without that update); the bulletins require at least 5,000 miles. With only P0420/P0430, perform the cylinder air-fuel test and replace the injectors only if it fails; 20-100 also requires its software update. With the specified misfire or air-fuel imbalance codes, follow the injector-replacement branch and any applicable software update. For a 9-speed automatic under 20-100, also confirm its A/T software is current. Use the complete specified fuel-injector kit (06160-RLV-305 in these bulletin versions), including all must-replace parts, rather than only the six injectors pictured. Honda’s extension is 10 years from original purchase or 150,000 miles, whichever comes first, with eligibility confirmed by the dealer. These sources do not direct automatic catalytic-converter replacement. If none of the listed codes is present, continue normal troubleshooting.
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)
- Honda Service Bulletin 20-100, Warranty Extension: MIL Comes On with DTC P0420/P0430, P030x, and/or P219A/B (With Software Update) (Version 2, February 11, 2021)tsb
- Honda Service Bulletin 21-010, Warranty Extension: MIL Comes On with DTC P0420/P0430, P030x, and/or P219A/B (Without Software Update) (February 11, 2021)tsb
- Honda owner letter: Warranty Extension (Without Software Update) for 2017-19 Pilot fuel injectorstsb
- Honda dealer notice: Warranty Extension: 2016 Pilot V6 Fuel Injectortsb
On the J35 V6, the rubber valve cover gaskets and the integrated spark plug tube seals harden and shrink with age and heat, allowing oil to weep onto the hot exhaust manifolds (burning-oil smell) and, more seriously, to pool down inside the spark plug wells. Oil saturates the ignition coil boots and shorts the spark, producing misfires and a Check Engine Light. The rear (firewall-side) bank is hardest to access, so the leak is often neglected until misfires appear.
Common Symptoms
- Burning oil smell from the engine bay
- Oily residue/grime on top of the valve covers
- Oil pooled in the spark plug wells
- Rough idle, misfire, and Check Engine Light
- Occasional blue smoke / slightly higher oil consumption
How to Fix
Replace both valve cover gaskets and the spark plug tube seals (gasket sets include the tube seals); clean oil from the spark plug wells and inspect/replace any oil-soaked ignition coil boots and fouled spark plugs. Parts are inexpensive ($40-$80 per set) but labor is significant on the rear bank.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Fel-Pro VS50773R complete valve-cover gasket setOEMFel-Pro VS50773R / PartsGeek 29982-05418108
Confirm package contents on arrival.
- Genuine Honda 12030-5G0-000 front head-cover gasket packageOEMHonda 12030-5G0-000
2016-2020 front/radiator-bank gasket and tube-seal branch Fitment/availability: 2016-2020 U.S. Honda Pilot 3.5L V6 front head cover; package includes the front cover gasket, tube seals and sealing washers.
- Genuine Honda 12050-5G0-000 rear head-cover gasket packageOEMHonda 12050-5G0-000
2016-2020 rear/firewall-bank gasket and tube-seal branch Fitment/availability: 2016-2020 U.S. Honda Pilot 3.5L V6 rear head cover; package includes the rear cover gasket, tube seals and screw grommets.
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 (2)
The 3.2L V6 used in the first-generation Passport relies on a timing belt service interval that many used examples miss. When the belt, tensioner, or water pump fails, owners report sudden no-starts, stalling, or catastrophic internal engine damage because the engine is interference-design. Forum history and repair databases repeatedly flag overdue timing-belt service as one of the most important reliability risks on these trucks.
Common Symptoms
- Ticking or chirping from timing cover area
- Coolant seepage from water pump
- Sudden engine stall
- Cranks but will not start
- Misfire after belt jump
- Overheating if water pump fails
How to Fix
Service records should be checked first; if the belt age is unknown, replacement of the timing belt, tensioner, idlers, water pump, and front seals is the standard preventive fix. If the engine suddenly died and now cranks unusually fast, a compression test and borescope inspection are needed to check for bent valves before installing new timing components. Replacing accessory belts and coolant during the same job is common because labor overlap is significant.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- AISIN TKH-012 timing-belt kit with water pumpOEMAISIN TKH-012
Complete preventive timing-drive and water-pump branch after service history and engine condition are established Fitment/availability: 1998-2002 U.S.
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
- TipIf there is no proof of timing-belt service on a newly purchased first-gen Passport, owners generally treat it as overdue and replace it immediately.
- TipDo the water pump, tensioner, idlers, thermostat, and coolant at the same time to avoid paying duplicate labor later.
Sources for this issue (1)
Aging 3.2L V6 Passports commonly develop oil leaks from the valve cover gaskets and spark plug tube seals. Owners report burnt-oil smell, oil on the cylinder head, and in some cases oil filling the plug wells and causing ignition misfires. This is a typical age-related failure on the Isuzu-sourced V6 and becomes more common as rubber seals harden with heat.
Common Symptoms
- burning oil smell
- oil on valve covers
- oil in spark plug wells
- engine misfire
- rough idle
How to Fix
Inspect the valve cover perimeter and plug wells for fresh oil, then replace the valve cover gaskets, tube seals, and grommets as a set. Clean oil from the plug wells, inspect ignition wires/coils and spark plugs for contamination, and replace any damaged ignition components. Verify crankcase ventilation is functioning so excess pressure does not worsen the leak.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- FEL-PRO VS50486R valve-cover gasket setOEMFEL-PRO VS50486R
Confirm the sealed package contains every tube seal/grommet required by the service procedure before st
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 (1)
P0305 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 P0305 mean on a Honda?
P0305 stands for "Cylinder 5 Misfire Detected." This code means the engine control module detected a misfire on cylinder number 5, meaning that cylinder is not burning its air-fuel mixture properly on some combustion cycles. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder fails to fire correctly. A misfire wastes fuel, can make the engine run rough or shake, and dumps unburned fuel into the exhaust, which can overheat and damage the catalytic converter. It generally points to a problem with spark, fuel delivery, or compression specifically affecting cylinder 5. On Honda it is documented across 3 models: Ridgeline, Pilot, Passport.
What are the most common causes of P0305?
The most common causes of P0305 are: Worn or fouled spark plug on cylinder 5, Failed ignition coil or coil pack for cylinder 5, Faulty or clogged fuel injector on cylinder 5, Vacuum or intake air leak affecting that cylinder, Bad spark plug wire or boot (on applicable engines), Low compression from worn rings, valves, or head gasket, Carbon buildup or sticking valve on cylinder 5, Lean or rich fuel condition affecting the cylinder. The specific cause varies by vehicle.
How much does it cost to fix P0305 on a Honda?
Published repair estimates on Honda range from $120 to $8,000 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.