P0308 code: Cylinder 8 Misfire Detected
P0308 means cylinder 8 Misfire Detected. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0308 means
A misfire means a cylinder isn't burning its air-fuel mixture properly. P0308 points to one specific cylinder — number 8 — which makes it easier to diagnose than a random misfire. The usual cause is that cylinder's spark plug or ignition coil; a quick test is to swap the coil or plug with a neighboring cylinder and see if the misfire follows. Less commonly it's a clogged or dead fuel injector, or low compression in that cylinder from a valve or ring problem. Because unburned fuel can overheat the catalytic converter, a steady misfire shouldn't be left for long.
P0308 symptoms
- Rough idle or shaking, often felt at a stop
- Loss of power or hesitation under acceleration
- Flashing check-engine light during an active misfire
- Reduced fuel economy
- Engine may stumble or be hard to start
What it costs to fix P0308
Typical range: $80–$600 · about ~0.3–3 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Spark plug (single) | $4–$30 | ~0.3–1.5 hrs |
| Ignition coil (single) | $30–$150 | ~0.3–1 hrs |
| Fuel injector (single) | $100–$400 | ~1–3 hrs |
A single plug or coil is the cheap, common fix; an injector is pricier; low compression (a valve or ring issue) is a major repair that varies too much to quote — get it diagnosed if plug, coil, and injector all check out.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0308 for my exact vehicle →
How to fix P0308
Moderate — doable at home with common tools and patience
- Identify cylinder 8's bank and position
Cylinder 8 exists only on V8 (and larger) engines, and its location depends on the maker's numbering convention — it's often the rearmost cylinder on one bank, closest to the firewall. Verify with a diagram for your engine so every later test targets the right hole.
- Do a coil swap from cylinder 8
Move coil 8 onto another cylinder, clear the code, and drive the truck or car normally for a day. If the misfire code re-appears wearing the new cylinder's number, replace that coil; if P0308 returns unchanged, the coil is fine.
- Service the number 8 spark plug
The rearmost plug on a V8 is often the most neglected because it's the hardest to reach — inspect it for wear, fouling, and gap, and replace it while you're there. A swivel socket and patience beat forcing a straight extension into a tight corner.
- Verify fuel delivery to cylinder 8
Confirm injector 8 clicks rhythmically at idle or compare its resistance to the other injectors. A single dead injector produces exactly this kind of isolated, persistent single-cylinder code.
- Get a compression and leak-down verdict
If spark and fuel both check out and P0308 keeps returning, have cylinder 8's compression tested and, if it's low, a leak-down test performed. That result — intake valve, exhaust valve, rings, or gasket — determines whether the repair is worth it on your vehicle.
DIY or shop? If you can physically reach cylinder 8 — usually the deepest corner of the engine bay — the coil swap and plug change are ordinary DIY tasks. Tight van and luxury-car engine bays, direct-injection fuel systems, and any low-compression finding are all good reasons to let a shop take it from there.
Tools for the DIY steps: OBD-II scanner · Spark plug socket with swivel joint · Long and wobble extensions · Multimeter · Torque wrench
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0308.
Start a case with P0308 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0308?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0308: common questions
Can I drive with P0308?
That isn't something a code can tell you on its own. With a steady (not flashing) light, get it looked at soon. If the light is flashing, the active misfire is dumping raw fuel into the catalytic converter and can destroy it; stop driving and have the car towed.
How do I know if it's the coil or the spark plug?
Swap cylinder 8's coil (or plug) with a neighboring cylinder and clear the code. If the misfire moves to the other cylinder, the part you moved is the culprit — a cheap way to avoid replacing the wrong thing.
How much does it cost to fix P0308?
Often modest — a single spark plug or coil is the common, inexpensive fix. It rises if the cause is a fuel injector, and a compression problem (valve or ring) is a major repair that varies widely. Confirm the cause before spending.
Should I replace all the coils or just cylinder 8?
If only cylinder 8 is misfiring, replacing just its coil/plug is reasonable. Some owners replace all of them at once if the parts are old and high-mileage, to avoid chasing the next one — but it isn't required to fix P0308.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0308 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0308 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.