What does P0307 mean?
The engine control module detected repeated misfires specifically in cylinder 7.
Quick Decision Guide
- Worn or fouled spark plug in cylinder 7
- Failing ignition coil on cylinder 7
- Clogged or leaking fuel injector on cylinder 7
When to stop driving
If the check-engine light is flashing, stop driving immediately — active misfires are destroying the catalytic converter in real time. A solid light is less urgent but should be diagnosed within days.
Reviewed by ratchit Automotive Solutions for clarity and inspection-first safety framing. Not a substitute for professional diagnosis.
Repair Decision & Cost Guide
Use this guide to decide what to inspect first, what it may cost, and when to move from DIY checks to professional diagnosis.
P0307 points to a misfire condition, not a guaranteed failed coil or plug. Isolate the failing cylinder before buying parts.
DIY vs. Shop
Can you keep driving?
Best first DIY check
Don't replace this first
When to seek a shop
Recommended next action
Estimated Repair Cost
Inspection cost
$0–$25 DIY scanner
DIY parts cost
$5–$130
Inspect first before replacing parts.
If the vehicle is unsafe to drive, stop driving and seek professional help.
Shop diagnostic cost
$80–$150 (typical shop diagnostic fee)
Shop repair cost
$60–$550
Diagnostic uncertainty: This code points to a system or condition, not a guaranteed failed part. Inspect before replacing.
Cost variation: Costs vary by vehicle, location, part quality, labor rate, and the confirmed root cause.
Inspect Before Replacing
These checks are cheap, fast, and rule out the most common causes before spending money on parts.
- 1Swap the ignition coil from cylinder 7 with another cylinder on the same bank. Clear the code and drive.
- 2Unlatch the coil and injector connectors at cylinder 7 and inspect for spread pins, corrosion, or heat damage before ordering parts.
Track this misfire issue
Save this issue to My Garage, track what you inspect, and build service history for this vehicle.
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ratchit AI Insight
· P0307What this usually means:P0307 narrows the misfire to a specific cylinder, but the cause still needs to be confirmed before replacing parts. Misfire codes do not automatically mean spark plugs or coils are bad — air/fuel, vacuum, fuel delivery, and mechanical issues can all trigger the same code.
Common mistake: Many drivers replace all the spark plugs and coils first. That sometimes fixes it, but if the real cause is a vacuum leak, an injector problem, or low compression, the misfire returns and the parts money is wasted.
Inspect before replacing parts
- 1Check for a flashing check-engine light — a flashing CEL during a misfire is a high-risk condition for the catalytic converter.
- 2Swap the suspect coil/plug to a known-good cylinder and re-scan to see if the misfire follows.
- 3Inspect for obvious vacuum leaks, cracked intake boots, and disconnected PCV hoses.
- 4Review fuel trims and injector behavior before assuming an ignition part is bad.
Confirming the cylinder and the system (ignition vs. air/fuel vs. mechanical) before buying parts usually keeps the repair in the $20–$200 range instead of replacing a full ignition set.
Safety threshold: If the check-engine light is flashing, stop driving as soon as it is safe — continued driving in this state can damage the catalytic converter.
AI-assisted guidance reviewed against ratchit's inspection-first safety rules. Codes are clues, not confirmed diagnoses — always verify before replacing parts.
Understanding P0307 in detail
P0307 flags cylinder 7 as the cylinder repeatedly missing power strokes. Where cylinder 7 sits and how it is fired vary by manufacturer, so this page emphasizes the checks that apply no matter the engine layout. The most under-inspected failure mode on any single-cylinder misfire is not the coil — it is the wiring and connectors that feed it. Heat cycling loosens connector pin tension, harness routing near the exhaust hardens the insulation, and a hairline break in the injector or coil trigger wire can produce an intermittent misfire that a bench-test of the coil or injector will not reproduce. Before ordering a coil for cylinder 7, unlatch the connector, look for green corrosion or spread pins, wiggle-test the harness with the engine running, and confirm continuity from the connector back to the ECM pinout for that cylinder. Only then run the coil-swap test, plug read, and fuel/compression checks. Note: some manufacturer service bulletins address wiring harness routing or coil connector supersessions on specific year/make/model vehicles — checking for related service information before parts replacement is worthwhile.
Symptoms of P0307
- Check engine light on or flashing
- Rough idle with noticeable vibration
- Loss of power during acceleration
- Engine stumbling or hesitation
- Fuel smell from exhaust
Common causes
- Worn or fouled spark plug in cylinder 7
- Failing ignition coil on cylinder 7
- Clogged or leaking fuel injector on cylinder 7
- Degraded spark plug wire (on wire-to-plug systems)
- Low compression in cylinder 7 (valve or ring issue)
How to diagnose P0307
Steps ordered by urgency — tackle Now items first.
- NowSwap the ignition coil from cylinder 7 with another cylinder on the same bank. Clear the code and drive.
- NowUnlatch the coil and injector connectors at cylinder 7 and inspect for spread pins, corrosion, or heat damage before ordering parts.
- SoonIf coil and plug are good, test the fuel injector resistance and spray pattern.
- LaterPerform a compression test on cylinder 7 if all ignition and fuel components pass.
How to fix P0307
Fixes listed in order of likelihood and cost-efficiency.
- 1Replace spark plug in cylinder 7
- 2Replace ignition coil on cylinder 7
- 3Replace spark plug wire (if applicable)
- 4Replace or clean fuel injector
- 5Address low compression (valve job or piston rings)
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Recommended tools & parts
These recommendations appear because this issue commonly requires inspection in this system area. ratchit does not recommend replacing parts until the likely cause is confirmed.
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Estimated Repair Cost — P0307
Ranges vary by vehicle, region, and shop. Use as a ballpark — always get a quote.
DIY estimate
$5 – $25
Shop estimate
$60 – $200
DIY estimate
$25 – $80
Shop estimate
$120 – $350
DIY estimate
$40 – $130
Shop estimate
$200 – $550
Cost data is estimated and may not reflect your specific vehicle or location.
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Frequently Asked Questions
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