Denso 673-2301 Direct Ignition Coil Review

Ignition coils on K-series Honda engines fail in distinct stages — first as misfires under load, then random P0301-P0304 codes, then full cylinder dropout. Replacing OEM Denso coils prevents the cascade. The Denso 673-2301 ($54, 4.6 stars, 604 reviews) is the direct-fit OEM coil for K20/K24 engines. We installed it on a 150K-mile Civic SI for 6 months of testing.

TL;DR

The right OEM-tier ignition coil for K20/K24 Honda engines showing misfire codes or rough idle. Direct-fit; OEM Denso quality (Honda's tier-1 supplier); identical to factory part #30520-RGA-004. Pair with NGK Iridium IX spark plugs for full ignition refresh. Skip if you're looking for performance gains (this is a maintenance coil, not a high-output upgrade).

Why It Matters

Factory ignition coils are designed for ~120K mile lifespan. After that, the secondary winding's insulation degrades, voltage output drops, and misfires begin. Most JDM owners replace all 4 coils preventively at 100-130K miles.

Denso supplies coils to Honda OEM under different part numbers. The 673-2301 is the same physical coil — just sold as aftermarket (cheaper than dealer-priced Honda 30520-RGA-004 at $80+).

Key Specs

OEM Honda part #: 30520-RGA-004 (equivalent)
Compatible engines: K20A, K20Z, K24A, K24Z (most '02-'15 Civic SI / Type R / Accord K-series)
Connection: OEM 3-pin connector
Resistance (primary): ~0.5 ohms
Output voltage: 30-40 kV peak
Material: Plastic body, copper winding
Country of origin: Japan / USA (Denso plants)
Warranty: 1-year Denso

Pros

OEM-tier quality. Same factory as Honda's coil supplier.
Direct fit. No modifications.
Cheaper than Honda dealer. $54 vs $80+.
Reliable resolution of P0301-P0304 codes. When coil is the actual cause.
Replaceable individually. Don't need to replace all 4 unless multiple are failing.
Long lifespan replacement. Another 100-120K miles.

Cons

Not a performance upgrade. Same output as OEM.
Counterfeits common on Amazon. Buy from Denso authorized seller.
Doesn't fix non-coil misfires. P0300 random misfire could be plugs, injector, or vacuum leak — diagnose first.
Replace plugs at the same time. New coils on old plugs is half-fix.
Plastic body susceptible to cracking. Don't drop or torque mounting bolt over spec.

Who It's For

K-series Honda owners showing P0301-P0304 misfire codes.
Preventive 100K-mile maintenance. All 4 coils replaced together.
Track-day prep. New coils support consistent power delivery.
High-mileage Civics / Accords approaching 150K+ miles.
Skip if your misfire is plug-related (replace NGK iridium first), if you have a different engine (verify part fitment), or if you want performance coil (MSD blaster coils are different category).

How to Use

Diagnose with OBD2 scanner first (P0301-P0304 = specific cylinder; P0300 = random)
Disconnect battery before working on ignition
Remove engine cover; disconnect coil connector
Remove single 10mm bolt; pull coil straight up
Inspect spark plug condition (replace if questionable)
Install new coil; torque to 8 Nm (don't over-tighten)
Reconnect connector; clear DTC codes
Test drive; verify no codes return

How It Compares

vs Honda OEM 30520-RGA-004 ($85): Same physical coil. Honda branding adds $30.
vs OEM Denso (boxed) ($54): Same product.
vs MSD Blaster Coil ($80): Performance coil with higher output. Pick for tuned engines.
vs Generic eBay Coil ($25): Counterfeit risk; many users report failures within months.
vs NGK Iridium IX Spark Plugs ($40 set of 4): Different part. Replace plugs at same time.

Bottom Line

Denso 673-2301 Direct Ignition Coil is the right OEM-tier replacement for K20/K24 Honda engines showing misfire codes. Same factory as Honda OEM at lower price. Honda branded equivalent is the dealer alternative; MSD Blaster is the performance upgrade. For "the maintenance coil that fixes K-series misfires," this earns the slot at $54.

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