The P0304 code in your 2018 Nissan Altima indicates the engine control module has detected persistent misfires in cylinder 4. As a vehicle potentially carrying significant accumulated mileage, understanding both the standard causes and wear-related factors helps target diagnosis effectively.
Understanding P0304 in the 2018 Altima
The 2018 Altima offers the 2.5L four-cylinder and 3.5L V6 engine options. On the inline-four, cylinder 4 sits at the rear position. On the V6, cylinder numbering follows Nissan convention with cylinder 4 on the rear bank. Both engines have proven reliable but experience standard wear over the years since production.
Mileage-Related Misfire Causes
Vehicles of this age may approach or exceed spark plug replacement intervals. Ignition coils degrade from years of heat cycling. Direct injection (on the 2.5L) allows carbon accumulation over time. Fuel injector spray patterns may deteriorate with age and fuel quality variations. Consider the comprehensive maintenance history when diagnosing.
Diagnostic Approach
Identify your engine type and review maintenance records. Retrieve all codes and note the vehicle's current mileage context. Inspect spark plug condition—if original, replacement is overdue regardless of appearance. Test ignition coil output comparing cylinder 4 to others. Evaluate fuel system operation.
Repair Recommendations
Replace spark plugs with Nissan-specified components appropriate for your engine. Test and replace degraded ignition coils. Address fuel injector issues through cleaning or replacement. Consider comprehensive ignition system refresh if maintenance history is unknown.