Cylinder 3 Misfire Detected
The P0303 code means the vehicle's onboard diagnostic system has detected: Cylinder 3 Misfire Detected. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- medium
- Estimated cost
- $8-$30 per spark plug; $30-$80 per coil
The #1 fix for misfire codes. 15-piece set with 14mm, 16mm, 18mm magnetic sockets, T-handle extension, and spark plug gapper.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Read and clear misfire codes. Shows which cylinder is misfiring so you know exactly what to replace.
Check Price on AmazonAffiliate link -- we earn a commission at no extra cost to you.
Common Symptoms
- Rough idle
- Flashing CEL under load
- Power loss
- Fuel odor from exhaust
Probable Causes (Ranked by Likelihood)
- Faulty spark plug on cylinder 3 Very High
- Failed ignition coil on cylinder 3 High
- Clogged fuel injector on cylinder 3 High
- Low compression on cylinder 3 Moderate
Step-by-Step Diagnostic Procedure
-
Swap the cylinder 3 coil to an adjacent known-good position. If the misfire follows the coil, replace it.
-
Inspect and replace the spark plug on cylinder 3.
-
Perform injector balance test. Low contribution on cylinder 3 indicates an injector fault.
-
Compression test cylinder 3 if other fixes do not resolve the code.
Common Fixes by Vehicle
What techs usually find when diagnosing P0303 on specific vehicles — tap your vehicle for the fix and the exact part:
2009-2019 Dodge Ram/Chrysler 300 3.6L Pentastar Easy DIY
Cylinder 3 misfire on the Pentastar V6. Perform a coil swap test -- move the coil from cylinder 3 to another cylinder. If the misfire follows, replace the coil. If it stays on cylinder 3, check the spark plug and fuel injector. On high-mileage Pentastar engines, rocker arm failures on cylinder 3 are known -- listen for a ticking noise.
Labor: 20-30 min2011-2020 Ford F-150 3.5L EcoBoost Easy DIY
Cylinder 3 misfire on EcoBoost. Swap the ignition coil from cylinder 3 to verify. If coil is good, check for carbon buildup on the intake valve using a borescope -- direct injection engines are prone to carbon fouling. Also check the spark plug gap -- Ford spec is 0.028 inch for EcoBoost. Use Motorcraft SP-534 plugs only.
Labor: 20-30 min2010-2020 Chevrolet Silverado/GMC Sierra 5.3L Easy DIY
Cylinder 3 on the 5.3L is NOT an AFM cylinder, so lifter failure is less likely. Perform a coil swap test first (ACDelco D513A). If the coil and plug are good, check the fuel injector balance rate with a scan tool. Also check for a vacuum leak at the intake manifold gasket near cylinder 3. Compression test if all else checks out.
Labor: 20-30 min2002-2015 Nissan Altima/Maxima 3.5L VQ35DE Easy DIY
Cylinder 3 misfire on the VQ35DE V6. Check the ignition coil (Hitachi IGC0007) and spark plug first. Cylinder 3 is the rear bank center cylinder. If coil and plug are good, check for a clogged fuel injector. Seafoam fuel system cleaner can help if the injector is partially clogged. A compression test will rule out internal engine damage.
Labor: 30 minFrequently Asked Questions
Is cylinder 3 the same location on every engine?
No. Cylinder numbering varies by engine configuration and manufacturer. On V6 engines especially, cylinder 3 may be on either bank. Always consult your vehicle service manual.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0303 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
See All Codes & Fixes for Your Vehicle
Explore More
Was this helpful?
Share carcodefinder.com with a friend who needs to decode their check engine light.