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What P0304 means for your Honda Accord
Your Accord's ECM detected that cylinder 4 isn't firing properly - the crankshaft position sensor saw the rotational speed dip slightly each time cylinder 4 was supposed to combust. On the K24 Accord, P0304 is usually a worn cyl-4 ignition coil or plug. On the V6, cyl 4 is the rear-bank passenger end and tied directly to VCM-related wear. On the 1.5T, suspect fuel dilution.
🎯 Top Causes on the Honda Accord
50%
#1 CAUSE
VCM Rear-Bank Damage (3.5L V6)
Honda VCM deactivates rear-bank cylinders during cruise. On the 2008-2017 V6 Accord, cyls 4, 5, 6 are the rear bank and rotate through deactivation - all three develop ring/cylinder wear from one-sided seating. Cyl 4 commonly shows compression loss first because it cools fastest when deactivated. The result: oil consumption + P0304. Permanent fix is VCMTuner II ($300) to disable VCM; if compression is already low, only a short-block restores power.
VCMTuner II
$280-$340
Compression Test
$80-$150
Short-Block (worst)
$3500-$6000
30%
#2 CAUSE
Cylinder 4 Coil or Plug
K24 Accord coils (Hitachi OEM) fail between 90k-140k miles. Cyl-4 is at the transmission end and runs warm. Swap with cyl-2 to confirm. Use NGK U5167. Plugs are NGK ILZKR7B11 spec'd for 105k miles. On the 1.5T, use only Honda-spec NGK or Denso plugs - torque to 13 ft-lbs and never reuse.
OEM Coil
$70-$120
Aftermarket
$45-$70
w/Labor
$120-$260
20%
#3 CAUSE
Fuel Dilution Cyl-4 Wash (1.5T)
2018-2022 Accord 1.5T fuel dilution. Cold-climate cars get gasoline wash on cyl 4 (the cylinder with the longest injector run from the rail) during cold starts, causing soft compression and P0304. Honda TSB 18-114 family includes ECM updates and extended powertrain warranty for affected VINs. Oil change with full synthetic 0W-20 helps short-term.
Oil Change
$60-$90
Software Update
$0 (warranty)
Ring Job (worst)
$3000-$5000
🚗 Most Affected Accord Model Years
| Year | Engine | Primary Cause | Typical Mileage | Notes |
|---|---|---|---|---|
| 2008-2012 | 3.5L J35Z2 (VCM) | VCM rear-bank wear | 80k-140k | VCMTuner II recommended |
| 2013-2017 | 3.5L J35Y1 (Earth Dreams) | VCM-related | 70k-130k | Same VCM family |
| 2008-2017 | 2.4L K24W | Coil + plug | 100k-160k | Very reliable |
| 2018-2022 | 1.5L L15B7 Turbo | Fuel dilution | 30k-90k | Cold-climate worst |
| 2018-2022 | 2.0L K20C4 Turbo | Coil or DI carbon | 40k-90k | DI carbon at 60k+ |
🔧 How to Diagnose P0304 on a Honda Accord
- On a V6 Accord, check oil consumption AND compression. Burning over 1 qt/1000 mi + P0304 + low compression on cyl 4 = VCM damage. Install VCMTuner II to halt further wear; if compression below 130 psi, rebuild or short-block is the only fix.
- On a K24 Accord, swap cyl-4 coil with cyl-2. Clear code, drive. Misfire follows = bad coil. 80% of K24 P0304 cases resolve here.
- On a 1.5T Accord, smell the dipstick and check oil level. Above upper hash + gasoline smell = fuel dilution. Dealer ECM update + oil change under TSB warranty.
Want a step-by-step walkthrough specific to your Honda Accord? Run a $5.99 AI diagnosis report - we narrow the cause to your year, engine, and symptoms.
❓ Frequently Asked Questions
Is the V6 Accord VCM problem covered under warranty?
Honda has not issued a formal warranty extension for VCM oil consumption, despite a class-action settlement (Soto v. American Honda) that covered some VINs in select states. Most owners are out-of-pocket - $300 for a VCMTuner II is the cheapest preventive measure.
How much does P0304 cost to fix on an Accord?
K24 coil/plug: $120-$260. V6 with VCM-only damage: $300 (VCMTuner). V6 with low compression: $3500-$6000 short-block. 1.5T fuel dilution: $0 if under TSB warranty, otherwise an oil change.
Which cylinder is cylinder 4 on an Accord V6?
On the J35 V6, front bank is cyls 1-2-3 (radiator side) and rear bank is cyls 4-5-6 (firewall side). Cyl 4 is the passenger-side cylinder on the rear bank. To access it, you need to remove the upper intake plenum.
Will replacing only one coil fix it long-term?
On a K24 under 80k, yes. Over 100k, the other three coils are usually within 20k miles of failure - many owners replace all four at once for $180-$240 in parts and save labor down the road.
Can I block VCM without buying a VCMTuner?
Technically yes - you can unplug the VCM solenoid and clear codes - but the ECM will throw a check engine light. The VCMTuner II ($300) is the only clean way to disable VCM without triggering a CEL or affecting other systems.
See all P0304 causes (all vehicles) → · Related: Honda VCM V6 Oil Consumption →