HIGH System: Ignition & Misfire System SAE J2012 Standard

P0304: Cylinder 4 Misfire Detected

The ECM detects crankshaft speed drop on Cylinder #4. Cylinder 4 is closest to the transmission bellhousing on transverse inline 4-cylinder vehicles.

Driveability & Safety Advisory

Drive short distances only to repair shop. Avoid rapid acceleration.

Nissan NTB13-039 Target: 2007–2013 Nissan Altima / Sentra (2.5L QR25DE)

Factory Condition: Valve cover spark plug tube seal on Cylinder 4 leaks oil into spark plug well, shorting out ignition coil boot.

OEM Service Remedy: Replace engine valve cover assembly with integrated spark plug tube seals, clean well, and install new coil.

Cylinder #4 is located closest to the transmission bellhousing on 4-cylinder engines.

Cylinder 4 Misfires: > 20 counts

Compression: 155 – 180 psi

Coil Resistance: 0.8 – 1.4 Ohms

Injector Resistance: 12.0 – 14.2 Ohms

2010–2016 Toyota Camry / Corolla (1.8L / 2.5L)

Root Cause: Cylinder 4 ignition coil internal capacitor failure.

Verified Fix: Replace Cylinder 4 ignition coil.

Remove Cylinder 4 coil: Check for engine oil in the spark plug well.

Perform coil swap test with Cylinder 1.

Check spark plug gap.

DIY Replacement Parts: $35 – $110

Independent Repair Shop (Parts + Labor): $180 – $420

Standard Diagnostic Time: 1.0 – 2.0 Flat-Rate Hours

Recommended Parts: Ignition coil, Spark plug, Valve cover gasket (if oil present)

Required Test Tools: Spark plug socket, OBD2 scan tool

A leaking spark plug tube seal in the valve cover allows oil to submerge the plug, which grounds the spark voltage and causes misfires.