P0308

Universal

Cylinder 8 Misfire Detected

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The engine computer has detected that cylinder 8 is not contributing consistently to engine rotation. It infers this from changes in crankshaft speed; the code identifies the affected cylinder, not the cause. A misfire can reduce power and fuel economy, increase emissions, and, if severe or persistent, damage the catalytic converter.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the check-engine light is flashing, the engine is shaking severely, power is sharply reduced, or you smell raw fuel, stop driving when safe and arrange inspection. A continuing misfire can overheat and damage the catalytic converter. If symptoms are mild and the light is steady, drive gently only as needed to reach a repair facility.

Common Symptoms

  • The engine may idle roughly or shake because cylinder 8 is producing less power than expected.
  • Hesitation, reduced acceleration, or loss of power may occur when the misfire affects engine output.
  • Fuel economy may worsen if combustion is incomplete or engine control adjustments compensate for the misfire.
  • The check-engine light may turn on; it may flash when the misfire is severe enough to pose a catalytic-converter risk.
  • The vehicle may have no noticeable symptoms if the misfire is intermittent or mild.

Common Causes

  • A worn, fouled, damaged, or incorrectly functioning spark plug may prevent reliable combustion in cylinder 8.
  • An ignition coil, ignition wire, or related connection may fail to deliver a consistent spark, if fitted on the vehicle.
  • A fuel injector may be restricted, electrically faulty, or unable to deliver fuel consistently to cylinder 8.
  • Damaged wiring or a poor electrical connection may interrupt ignition or injector operation.
  • Low compression or another mechanical problem in cylinder 8 may prevent the air-fuel mixture from burning properly.
  • An air leak or mixture problem affecting the cylinder may contribute to a misfire.

Diagnostic Steps

  1. Check whether the check-engine light is flashing and note any shaking, fuel smell, or power loss. Stop driving if the misfire is severe or the light is flashing.
  2. With the engine off and cool, look for loose or visibly damaged electrical connectors and wiring around accessible ignition and fuel-system components. Do not pull on wiring or work near moving or hot parts.
  3. If you have a scan tool, record the stored and pending codes and freeze-frame information before clearing anything. Other codes and operating conditions can help identify the cause.
  4. Check the vehicle's service information to identify cylinder 8 and the correct inspection procedure; cylinder numbering varies by engine.
  5. If you are comfortable doing so and the service information supports it, inspect the cylinder 8 spark plug for visible damage or fouling. Do not replace parts based only on the code.
  6. If the cause is not apparent, have a technician test ignition, injector operation, wiring, and cylinder mechanical condition rather than guessing at a replacement.

When to Call a Professional

Confirm the code and review scan data and any related codes before replacing parts. A technician can compare cylinder contribution and inspect cylinder 8's ignition, fuel delivery, wiring, and mechanical condition. Depending on findings, useful tests may include checking spark, injector operation and control, compression, or leak-down. Exact test procedures depend on the vehicle's engine and service information.

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Commonly Asked Questions

Does P0308 prove that the cylinder 8 ignition coil is bad?

No. The code reports a misfire detected in cylinder 8, but the cause could involve ignition, fuel delivery, wiring, compression, or another condition. Testing is needed before choosing a repair.

Can I keep driving with P0308?

It depends on how the engine is running. A flashing check-engine light, severe shaking, raw-fuel smell, or major power loss calls for stopping when safe and arranging service. A persistent misfire can damage the catalytic converter.

Why does the code identify a cylinder rather than a failed part?

The engine computer detects uneven crankshaft speed that it associates with a cylinder's contribution. That monitoring can identify cylinder 8 as the affected cylinder, but it cannot by itself distinguish among possible causes.

Could P0308 appear without obvious symptoms?

Yes. An intermittent or mild misfire may be detected before it is easy to feel. Scan data and inspection can help determine whether it is active and what conditions are associated with it.

Does cylinder 8 have the same location on every engine?

No. Cylinder numbering and access vary by engine. Use the vehicle's model-, year-, and engine-specific service information before identifying or removing components.

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