P0307
- Powertrain
- Generic (SAE)
- Emissions
Get it looked at now
A flashing lamp means the misfire rate is high enough to overheat and destroy the catalytic converter within minutes of driving. A steady lamp with an occasional misfire is less urgent but still real: causes worsen, and if the underlying fault is a failing deactivation lifter the damage can extend to the camshaft lobe and circulate metal through the engine.
- Safe to drive
- Flashing light: stop and tow. Steady light with a mild stumble: drive gently to diagnosis, avoiding towing, hills and full throttle.
Cylinder 7 Misfire Detected
Cylinder 7 is misfiring — the computer detected the crankshaft not getting its expected push from that cylinder. Only engines with seven or more cylinders can set this, so you are looking at a V8, V10, or V12. The code names the cylinder, not the cause.
Misfire monitoring measures crankshaft acceleration through each combustion event and assigns shortfalls to the responsible cylinder. A single-cylinder code moves shared causes — fuel pressure, mass airflow, a central vacuum leak — down the priority list and puts that cylinder's own coil, plug, injector, wiring, valvetrain, and compression at the top. On V8s equipped with cylinder deactivation, an additional cause deserves early attention: a collapsed or failed deactivation lifter, or a stuck lifter oil control solenoid, produces a hard misfire on a specific cylinder that ignition parts will never fix. Which cylinders are deactivated, and which physical cylinder is number 7, both vary by engine.
How the car detected itCrankshaft velocity variation accumulated over two rolling windows — a short window at a catalyst-damaging misfire rate that flashes the malfunction indicator lamp, and a longer window at the emissions-threshold rate that lights it steady. Rough road, low fuel, and hard shift conditions are typically masked out to prevent false detection. On engines with cylinder deactivation the strategy also has to distinguish commanded deactivation from genuine misfire. Thresholds and windows are vehicle-specific.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Flashing light: stop and tow. Steady light with a mild stumble: drive gently to diagnosis, avoiding towing, hills and full throttle.
- Urgency
- Get it looked at now
- Will it pass emissions
- No
- If ignored
- The catalytic converter overheats and melts, adding a large part to the repair. Unburned fuel washes the bore and dilutes the oil. On a cylinder deactivation engine, a failing lifter that is left running can wipe its camshaft lobe and send debris through the oil system, escalating from a lifter replacement to a camshaft and cleanup job or worse.
- Check engine light
- Solid
- Clearing the light
- A completed drive cycle is normally required before the monitor re-runs and the light can clear.
- Check engine light on or flashing
- Rough idle and uneven running
- Power loss, hesitation under acceleration
- Increased fuel consumption
- Possible smell of unburned fuel from exhaust
Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Ignition coil failed | Very common | — |
| 2 | Spark plug worn or fouled | Very common | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
Whether the check engine light is flashing or steady
It decides tow versus drive, and it is visible without any tools. A flashing lamp is a catalyst-damaging misfire happening right now.
Whether this engine uses cylinder deactivation, and whether cylinder 7 is one of the deactivated cylinders
On affected V8s, a collapsed deactivation lifter is a leading real-world cause of a single-cylinder misfire. Which cylinders deactivate varies by engine, so check service information rather than guessing.
Freeze frame — engine speed, load, and coolant temperature at the set
Misfire under load points at a coil breaking down under cylinder pressure or weak compression. Misfire at idle only points at vacuum leaks or a lifter. Cold-only points at fuel or a cracked coil.
A ticking or clattering noise from that bank, and current oil level and condition
A distinct tick alongside a single-cylinder misfire strongly suggests valvetrain — a collapsed lifter, a broken spring, or a rocker fault — not ignition. Low or degraded oil is a known trigger for deactivation lifter failure.
Misfire counters on all cylinders, plus fuel trims per bank
Neighbors also counting suggests a shared cause on that bank. Lean trims on one bank point at an intake or exhaust leak rather than a single ignition part.
Confirm which physical cylinder is number 7 and which bank it sits on
Tools Service information for the specific engine
V8 numbering conventions differ between manufacturers. Confirm the position, the bank, and the firing order before removing a single part.
ExpectedA confirmed cylinder position and bank. Never work from assumption on a V8.
Swap the coil and plug with another cylinder, clear codes, and re-run
Tools Basic hand tools, spark plug socket, torque wrench, scan tool
This resolves the most common causes fastest. Move one part at a time where you can so the answer is unambiguous.
ExpectedThe code following the swapped part identifies that part. The code staying on cylinder 7 shifts the investigation to that cylinder itself, its injector, or its valvetrain.
Inspect the removed plug and its well
Tools Inspection light, gap gauge
Look for oil or coolant in the well, a carbon-tracked or split boot, and read the plug's electrode, gap, and deposits against a plug from a healthy cylinder.
ExpectedDry well, intact boot, even light-brown deposits and a gap within the vehicle's specification. Oil fouling points at stem seals or rings; coolant staining at a head gasket.
Verify coil power and trigger signal at the connector
Tools Digital multimeter or lab scope, backprobes, wiring diagram
Test with the circuit loaded and compare directly to a working cylinder. Broken terminals and chafed trigger wires imitate a failed coil precisely.
ExpectedBattery voltage on the feed and a clean trigger pulse matching the other coils. Pin identification is vehicle-specific.
Test the injector for that cylinder against the others
Tools Digital multimeter, mechanic's stethoscope
Compare winding resistance across all injectors under the same conditions and listen with a stethoscope for a regular click while running.
ExpectedResistance consistent with its siblings and an audible click. Absolute values are engine-specific — the comparison across cylinders is the meaningful test.
On a cylinder deactivation engine, evaluate the lifter and its oil control circuit
Tools Scan tool with bidirectional control, mechanic's stethoscope, oil pressure gauge, hand tools
Listen for a tick at that cylinder, command deactivation on and off with the scan tool if the vehicle supports it, and check oil pressure and the lifter oil control solenoid operation. Removing the valve cover to check rocker and valve movement is the definitive check.
ExpectedEven valve motion on that cylinder matching its neighbors, and normal deactivation response. A rocker with no lift, excessive lash, or a lifter that will not return to full travel confirms a collapsed deactivation lifter. Oil pressure specifications are engine-specific.
Test compression, then leakdown if compression is low
Tools Scope with amp clamp, compression gauge, leakdown tester
Relative compression during cranking with an amp clamp is the quickest screen. Follow with a conventional compression test and, if needed, a leakdown test to locate the loss.
ExpectedCylinders reasonably consistent with one another. Variation limits are engine-specific — many manufacturers allow up to about 25 percent between the highest and lowest cylinder, while a tighter spread is typical of a healthy engine. Use the manufacturer's stated variation limit and treat one cylinder clearly below its neighbors as a reason to run leakdown, not as a diagnosis. Leakdown air at the intake means an intake valve, at the tailpipe an exhaust valve, at the oil filler rings. Absolute figures are engine-specific.
Smoke-test the intake for that bank if trims were lean
Tools Smoke machine
Look for smoke at the manifold gasket near that runner, at the injector seals, and around any vacuum or PCV connection on that side.
ExpectedNo escaping smoke. A leak local to that runner accounts for both a lean bank and a single-cylinder misfire.
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Replace the spark plug for that cylinder, or the full set at service age | A worn, fouled, cracked, or misgapped plug found, with the misfire ending on a known-good plug | $150–$450 | DIY |
| Replace the ignition coil for that cylinder | The misfire following the coil when swapped to another cylinder | $120–$400 | DIY |
| Repair the coil harness, connector, or trigger circuit | Missing power or a corrupted trigger at the coil connector, with the coil itself proven good on another cylinder | $100–$400 | DIY |
| Clean or replace the fuel injector for that cylinder | Injector resistance or flow out of line with its siblings, or the misfire following the injector on a swap | $200–$700 | DIY |
| Replace the failed cylinder deactivation lifter and inspect the camshaft lobe | No valve lift or abnormal lash observed on that cylinder with the valve cover off, or a lifter that will not return to full travel | $1,500–$4,000 | Shop |
| Replace the lifter oil control solenoid or manifold | The solenoid failing to change lifter oil pressure when commanded, with the lifter itself proven mechanically sound | $300–$900 | Hard |
| Cylinder head or valve repair | Compression on that cylinder outside the manufacturer's stated variation limit, with leakdown air audible at the intake or exhaust port and no improvement from a wet test | $1,500–$4,000 | Shop |
US independent shop rates, parts plus labor. V8 plug and coil work is generally accessible on trucks and rear-drive cars, but tight engine bays and exhaust manifold clearance can add hours. Cylinder deactivation lifter repairs are the expensive outcome here: if the camshaft lobe is damaged, add camshaft replacement and a thorough oil system cleanup. A cooked catalytic converter adds further cost on top of whatever caused the misfire.
- Replacing coils and plugs repeatedly on a cylinder deactivation V8 when the actual fault is a collapsed lifter. If ignition parts do not fix it, stop buying ignition parts.
- Assuming cylinder 7 is in a particular position. V8 numbering and bank assignment vary by manufacturer and the wrong cylinder wastes the entire job.
- Driving with a flashing lamp, converting a coil-and-plug repair into a catalytic converter repair.
- Ignoring a ticking noise that accompanies the misfire. Valvetrain noise plus a single-cylinder misfire is a strong pattern, and it changes the entire diagnostic path.
- Replacing all eight coils because one is suspected, when a swap test would have identified the failed one.
- Skipping the plug inspection. Its appearance frequently narrows the cause to fuel, oil, coolant, or ignition.
- Condemning the cylinder on a rule-of-thumb compression spread rather than the manufacturer's stated variation limit.
- Declaring the repair complete after an idle test when the freeze frame showed the misfire occurred only under load.
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
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