What does code P0304 mean on a Subaru and is it safe to drive?
P0304: Cylinder 4 Misfire Detected. Here's what it means on your Subaru, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
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What this code means
Misfire confirmed on cylinder 4. On 4-cylinder engines, this is the last cylinder—check coil and plug first, then injector, then compression.
Common causes for your Subaru
- Worn spark plug on cylinder 4
- Failed ignition coil on cylinder 4
- Faulty or clogged fuel injector
- Low compression or valve issue
Symptoms
- Check Engine Light
- Rough idle and shaking
- Poor acceleration or power loss
Typical fixes
- Replace spark plug and COP coil on cylinder 4
- Clean or replace fuel injector
- Compression and leak-down test if basic parts check out
Repair cost range
For a Subaru, repairs for P0304 often fall between $150 and $900, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Subaru
On Subaru's flat-four, cylinder 4 is the rear cylinder on the left bank. Head gasket leaks at this location are well documented on EJ25. A compression test and coolant system pressure check should precede ignition diagnosis on any P0304.
Most commonly affected models
Impreza EJ204 2002–2007Outback EJ25 2000–2009Forester EJ25 2006–2010