P0308

OBD2 code P0308 indicates that your vehicle's engine control module (ECM) has detected a misfire in cylinder 8. A misfire occurs when the air-fuel mixture in a cylinder fails to ignite properly or at the correct time, resulting in incomplete combustion. Cylinder 8 is typically found in V6, V8, or larger engines, and this specific diagnostic code pinpoints the problem to that individual cylinder. The ECM monitors engine performance through the crankshaft position sensor, and when it detects that cylinder 8 is not contributing its expected power, it triggers the P0308 code and illuminates the Check Engine Light.

This code matters because continued driving with a cylinder misfire can lead to several problems. First, unburned fuel can pass into the exhaust system and damage the catalytic converter, an expensive component that can cost $1,000-2,500 to replace. Second, misfires cause rough running that puts additional strain on engine mounts and other components. Third, you'll experience reduced fuel economy, diminished performance, and increased emissions that may cause your vehicle to fail emissions testing. If the Check Engine Light is flashing rather than steady, this indicates a severe misfire that can cause immediate catalytic converter damage.

When you encounter code P0308, the best course of action is to address it within 1-2 weeks, though you can continue driving carefully in the meantime. Start with the simplest and most common fixes: inspect and replace the spark plug for cylinder 8, check the ignition coil, and look for obvious vacuum leaks. Many car owners with basic mechanical skills can handle spark plug and coil replacement themselves. If these simple fixes don't resolve the issue, or if a compression test reveals low compression in cylinder 8, you may need professional diagnosis to determine whether fuel injector problems, valve issues, or more serious internal engine damage is to blame. Early diagnosis and repair will save you money and prevent more extensive engine damage down the road.

Severity

Symptoms

• •Rough idle or noticeable engine vibration
• •Check Engine Light (CEL) illuminated and possibly flashing
• •Reduced engine power and acceleration
• •Poor fuel economy and increased emissions
• •Engine hesitation or stumbling during acceleration
• •Strong smell of unburned gasoline from exhaust

Likely Causes

Estimated Cost

Common Fixes

1. Replace spark plug on cylinder 8 ($15-50 DIY, $100-200 professional)
2. Replace ignition coil for cylinder 8 ($50-150 DIY, $150-350 professional)
3. Clean or replace fuel injector on cylinder 8 ($20-80 for cleaner DIY, $200-500 professional replacement)
4. Repair vacuum leak or replace intake manifold gasket ($30-150 DIY, $300-800 professional)
5. Compression test and engine repair if mechanical failure detected ($50 for DIY gauge, $800-2500+ professional)

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