P0305 means cylinder 5 specifically is misfiring — failing to burn its fuel-air mixture properly — which is a diagnostic head start over the random, multi-cylinder pattern of P0300. Cylinder 5 only exists on six- and eight-cylinder engines, and the numbering and bank layout vary by manufacturer, so confirm which physical cylinder is meant before you remove anything.
What Does P0305 Mean?
The engine computer watches the tiny speed changes of the crankshaft and can tell when one cylinder is not contributing its share of power. P0305 is stored when that is happening on cylinder 5. The general explanation of misfires, and why unburned fuel is hard on the catalytic converter, is in our P0300 guide; the only difference here is that the problem is isolated to one cylinder, which makes diagnosis much quicker. The neighbouring single-cylinder codes are P0304 and P0306.
Cylinder numbering differs between manufacturers and between inline, V and flat engines, and cylinder 5 may sit on either bank. Check the firing order and layout diagram for your exact engine before swapping parts. A P0305 on a four-cylinder engine is unusual and worth a second scan.
Common Symptoms
- Check engine light on, flashing if the misfire is active and severe — see our flashing check engine light guide.
- A rough idle felt as a stumble or shake — see car shakes when accelerating for the broader picture.
- Hesitation or power loss under load.
- Worse running when cold in some cases — see engine runs rough only when cold.
- Poorer fuel economy and a raw-fuel smell in severe cases.
Common Causes, Most Likely First
- A worn or fouled spark plug in cylinder 5 — see our how often to replace spark plugs guide.
- A failed ignition coil or coil connector on cylinder 5.
- A clogged or failing fuel injector on that cylinder.
- A vacuum or intake leak near that cylinder’s intake runner.
- Low compression in that cylinder from a worn valve, piston ring or head gasket — the most serious cause, worth ruling out if the simpler ones do not fix it.
On V6 engines that shut cylinders down to save fuel, plugs on the cylinders that spend time deactivated can foul faster — see our Honda Pilot guide for one well-documented example.
How to Diagnose It
- Swap the coil from cylinder 5 with a neighbouring cylinder’s and clear the code. If the misfire code follows the coil, the coil is the fault.
- Inspect and, if worn, replace the plug — compare it with the others.
- Check the coil connector and wiring for corrosion or damage.
- Test or swap the injector if plug and coil are ruled out.
- Run a compression test on cylinder 5 if the electrical and fuel causes are cleared.
A scan tool that shows live misfire counts makes this faster — see our OBD-II scanner guide.
Never work under a vehicle supported only by a jack. Use axle stands on firm, level ground, chock the wheels that stay down, and leave the car in gear or Park with the handbrake on. A jack lifts; stands hold.
Possible Fixes
| Cause | Fix | Typical cost |
|---|---|---|
| Worn spark plug | Replace plug(s) | $40 – $200 |
| Failed ignition coil | Replace the coil | $100 – $300 |
| Clogged or failing injector | Clean or replace the injector | $150 – $450 |
| Intake or vacuum leak | Replace the hose or gasket | $50 – $350 |
| Low compression (mechanical) | Engine repair | $500 – $3,000+ |
Can I Drive With P0305?
For short trips only, gently. An active misfire sends unburned fuel into the catalytic converter, which can overheat and be damaged — see P0420 for what that failure looks like. If the check engine light is flashing, treat it as urgent and follow our flashing light guide.
When to See a Mechanic
Promptly if the light flashes or the misfire is rough. Tell the shop the code is cylinder-specific so they can start with a coil swap. More in our engine section.
Frequently Asked Questions
What does P0305 mean?
The engine computer has detected a misfire in cylinder 5 specifically, which makes diagnosis quicker than a random multi-cylinder misfire.
Can a four-cylinder engine set P0305?
It should not, because there is no cylinder 5. If a four-cylinder shows P0305, rescan or check with a better tool.
What is the fastest way to find the cause?
Swap the ignition coil with a neighbouring cylinder’s and see whether the misfire code moves with the coil.
Is it safe to drive with P0305?
Only for short trips and with care. A continuing misfire can damage the catalytic converter, so do not ignore it.
How much does it cost to fix P0305?
Often $40–$300 for a plug or coil, though a mechanical cause such as low compression costs much more.
