Cylinder 1 Misfire Detected
What does P0301 mean?
The P0301 code means the vehicle's onboard diagnostic system has detected: Cylinder 1 Misfire Detected. This is a serious severity code.
Common Symptoms
- Rough idle with a rhythmic shudder
- Flashing Check Engine Light under load
- Power loss on acceleration
- Smell of unburned fuel from exhaust
Probable Causes (Ranked by Likelihood)
- Fouled or worn spark plug on cylinder 1 Very High
- Faulty ignition coil on cylinder 1 High
- Clogged or failed fuel injector on cylinder 1 High
- Low compression on cylinder 1 Moderate
- Burnt or damaged valve on cylinder 1 Low
Step-by-Step Diagnostic Procedure
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Confirm cylinder 1 location in your specific engine (front-left on most inline engines, front-right passenger-side on common V8s -- consult your service manual).
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Swap the spark plug from cylinder 1 to a known-good cylinder. If the misfire follows the plug, replace all plugs.
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Swap the ignition coil from cylinder 1 with an adjacent coil. If the misfire code changes to the other cylinder number, replace the coil.
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Perform an injector balance test with a scan tool. A low or no contribution cylinder indicates a bad injector.
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Test compression on cylinder 1. Below 120 psi or more than 15% difference from other cylinders requires further investigation.
Frequently Asked Questions
How do I know which cylinder is cylinder 1?
On inline 4-cylinder engines, cylinder 1 is typically the frontmost cylinder (closest to the drive belt). On V6 and V8 engines the location varies by manufacturer. Always verify with a service manual or diagram before swapping components.
Will a misfire on cylinder 1 damage my engine?
A sustained misfire sends raw fuel into the exhaust, which can overheat and destroy the catalytic converter. A flashing CEL is a warning that damage is imminent. Address the misfire promptly.