P0305
Cylinder 5 Misfire Detected
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OBD2 trouble code P0305 indicates that your vehicle's powertrain control module (PCM) has detected a misfire in cylinder 5. A misfire occurs when the air-fuel mixture in a cylinder fails to ignite properly or at the correct time, resulting in incomplete combustion. The engine control module monitors this through crankshaft position sensors that detect variations in engine speed. When cylinder 5 consistently fails to fire correctly, the PCM stores code P0305 and illuminates the check engine light to alert you to the problem.
This code is moderately serious and should be addressed within one to two weeks. While you can typically continue driving with a cylinder 5 misfire, doing so risks damaging your catalytic converter (a costly repair), reducing fuel efficiency, and potentially causing damage to other engine components. The unburned fuel from the misfiring cylinder can wash oil from cylinder walls and contaminate your engine oil, leading to accelerated wear. Additionally, raw fuel entering the exhaust system can overheat and destroy the catalytic converter, turning a relatively inexpensive repair into a major expense.
The good news is that P0305 points to a specific cylinder, making diagnosis much easier than a random misfire code. Most causes are relatively simple and affordable to fix, especially if caught early. The most common culprits are worn spark plugs and failing ignition coils, both of which are straightforward repairs for DIY mechanics or professionals. If you notice rough idling, reduced power, or poor fuel economy along with your check engine light, it's time to diagnose and repair the issue before it leads to more expensive problems down the road.
Severity
Symptoms
- •Check Engine Light illuminated
- •Rough idle or engine vibration
- •Loss of power or acceleration
- •Poor fuel economy (10-25% decrease)
- •Engine hesitation or stumbling during acceleration
- •Strong smell of unburned fuel from exhaust
Likely Causes
Spark plugs wear over time and can become fouled with carbon deposits, preventing proper ignition. This is the most common cause of isolated cylinder misfires.
Ignition coils can fail due to heat, vibration, or age, resulting in weak or no spark delivery to the cylinder. This is especially common in high-mileage vehicles.
A clogged, leaking, or electrically failed fuel injector prevents proper fuel delivery to the cylinder, causing a misfire condition.
Worn piston rings, damaged valves, or a blown head gasket can reduce cylinder compression, preventing proper combustion even with good spark and fuel.
An intake manifold gasket leak near cylinder 5 can allow excess air into the cylinder, disrupting the air-fuel mixture and causing a misfire.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace spark plug in cylinder 5 ($15-40 for single plug, $60-200 for full set)
- Replace ignition coil or coil pack for cylinder 5 ($50-250 per coil)
- Clean or replace fuel injector for cylinder 5 ($50-150 for cleaning, $100-300 for replacement)
- Perform compression test and repair as needed (varies widely: $300-2000+ for major engine work)
- Repair vacuum leak or replace intake manifold gasket ($100-500)
Shop Parts
Videos
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