P0308: Cylinder 8 Misfire Detected
Key takeaways
- P0308 means the engine computer counted too many misfires on cylinder 8, so it only shows up on V8 and larger engines.
- If the check engine light flashes, stop driving: the misfire is sending unburned fuel into the catalytic converter.
- Most P0308 fixes are an ignition coil ($120–$300) or a set of spark plugs ($250–$600 on a V8).
- 12 complaints filed with NHTSA mention P0308; the GMC Sierra 1500 has the most, with 3.
- 172 manufacturer bulletins name P0308, including GM lifter failures on 2022 full-size trucks and engine-computer updates on Ram.
What P0308 means
Cylinder 8 is misfiring, meaning it isn’t burning its fuel properly on every stroke. Scanners call it Cylinder 8 Misfire Detected. The engine computer times each firing pulse off the crankshaft sensor; when cylinder 8 fails to speed the crank up the way the others do, often enough to cross the limit, it sets P0308.
P0308 only exists on engines with at least eight cylinders, which in practice means V8 trucks, SUVs and performance cars. A four- or six-cylinder car cannot set it, so a P0308 on one of those means the reader is set to the wrong vehicle.
Is it safe to drive?
Short trips only, and stop if the light is flashing. With a steady light and a slight shake, drive gently to a shop and avoid hard acceleration and towing. A flashing check engine light means the misfire is heavy and unburned fuel is heating up the catalytic converter, which can overheat and fail. Pull over when it is safe. Do the same if the engine shakes hard, loses power or you smell fuel. For what to do right now, see check engine light flashing.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Failed ignition coil | Swap coil 8 with a neighbor on the same bank; the code follows the coil | $120–$300 per coil |
| Worn or fouled spark plug | High mileage, wide gap, oil or carbon on the tip, cracked porcelain | $150–$350 a set (4-cyl), $250–$600 (V6/V8) |
| Clogged or leaking fuel injector | Coil and plug are good; injector test or stethoscope shows cylinder 8 is weak or silent | $250–$600 per injector |
| Vacuum leak near cylinder 8 | Lean code such as P0171 alongside; smoke test finds the leak | $50–$400 |
| Software fault | Matching bulletin for your engine; common on newer trucks | $100–$200, often $0 under warranty |
| Low compression (valve, ring, lifter, head gasket) | Compression or leak-down test on cylinder 8 reads low | $1,500–$4,500 |
What to check first
- Save the freeze-frame data before clearing anything. Cold, idle or load conditions point to different causes.
- Look for other misfire codes. One cylinder points to that cylinder’s parts; several, with P0300, point to fuel, vacuum or timing.
- Swap the coil with a neighboring cylinder on the same bank, clear, and drive. Code moves: coil. Code stays: plug next.
- Pull and read the plug. Check for oil in the plug tube, a torn boot, or a worn electrode.
- Test injector and compression only after coil and plug check out.
On V8 trucks, the rear plugs sit close to the firewall, so labor on a cylinder 8 job can run higher than on a front cylinder.
Across the bulletins, two patterns stand out. GM has diagnostic guidance for misfire codes P0300 to P0308 across many models, plus a bulletin for the 2022 Escalade and Silverado 1500 where a lifter came apart, fixed by replacing the lifter guide and four lifters. Stellantis has an engine-computer update for the 2023 Ram 1500 and a spark plug re-gap for the 2023 Dodge Challenger, and Ford has one for the 2024 Mustang Dark Horse setting P0308 after extended high-speed driving.
What it costs
The cheap outcome is one coil, $120–$300. The common outcome is a coil with a fresh set of plugs, $250–$600 for the plugs on a V8. The expensive outcome is low compression from a valve, lifter or head gasket, $1,500–$4,500. An hour of diagnosis, usually $100–$180, costs less than guessing through plugs, coils and injectors. You can also ask our AI mechanic to walk through your freeze-frame data first.
Related codes
P0308 often shows up with P0300 and with a neighboring cylinder such as P0306 or P0307. A lean code with it means look for a vacuum leak first. If the engine shakes along with the light, see check engine light and car shaking; for a shaky idle, see rough idle.
What owners report to NHTSA
12 complaints filed with NHTSA mention P0308, 10 of them since 2015, across 8 different models. The component owners most often filed it under: engine.
Most-reported models
| Vehicle | Complaints | Model years reported |
|---|---|---|
| GMC SIERRA 1500 | 3 | 2018, 2019 |
Manufacturer service bulletins that name P0308
171 technical service bulletins and manufacturer communications filed with NHTSA mention P0308, from 22 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- GENERAL MOTORS GENERAL MOTORS, bulletin 10172310: This Preliminary information communicates information that will need to be provided to TAC to aid in diagnosing if a vehicle comes in with misfire and DTC Codes P0300 - P0308 and/or P050D
- FORD MUSTANG (2024), bulletin 11007978: Some 2024 Mustang Dark Horse vehicles equipped with a manual transmission may exhibit an illuminated malfunction indicator lamp (MIL) with diagnostic trouble codes (DTCs) P0300, P0302 and P0308 stored in the powertrain c…
- RAM 1500 (2023), bulletin 10251871: Flash: Powertrain Control Module (PCM) Updates Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find one or more of the following Diagnostic Trouble …
- DODGE CHALLENGER (2023), bulletin 11005019: Spark Plug Re-Gap to Resolve Misfire Symptoms Customers must experience a Malfunction Indicator Lamp (MIL) illumination and the vehicle must exhibit/set one or more of the following Diagnostic Trouble Codes (DTCs): P0300…
- BUICK ALLURE (2006, 2016, 2017, 2018), bulletin 10206726: This Preliminary information communicates information that will need to be provided to TAC to aid in diagnosing if a vehicle comes in with misfire and DTC Codes P0300 - P0308 and/or P050D
- CADILLAC ATS (2013, 2014, 2015, 2016), bulletin 10206726: This Preliminary information communicates information that will need to be provided to TAC to aid in diagnosing if a vehicle comes in with misfire and DTC Codes P0300 - P0308 and/or P050D
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Can a V6 throw P0308?
No. Cylinder 8 only exists on engines with eight or more cylinders. If a four- or six-cylinder shows P0308, the scanner has the wrong vehicle selected or is misreading the computer.
Can I drive with P0308?
Gently, for short trips to a shop, as long as the check engine light is steady and the engine isn't shaking badly. A flashing light means stop, because a heavy misfire can overheat the catalytic converter.
Where is cylinder 8 on a V8?
It depends on the maker. Many GM and Chrysler V8s put cylinder 8 at the back of the passenger-side bank, while Ford numbers its V8s differently. Look it up for your engine before pulling parts.
What if P0308 comes back after a new coil and plug?
Then the problem is fuel, air or compression on that cylinder. The next steps are an injector test, a smoke test for vacuum leaks, and a compression or leak-down test. On some GM V8s a failed lifter shows up this way.
Why does P0308 show up with P0300?
P0300 is the random or multiple misfire code. If cylinder 8 is the only one named alongside it, start with cylinder 8's parts. If several cylinders are named, look for something they share, like a vacuum leak or fuel pressure.