P0305 Code: Cylinder 5 Misfire Detected

What the P0305 code means

The computer detects misfires by measuring the instantaneous change in crankshaft speed, and it identifies the specific cylinder where they happened. The P0305 code corresponds to cylinder five.

What sets this code and the ones after it apart is that they only appear on engines with six cylinders or more. On a transverse V6, very common in sedans and SUVs, cylinder five is usually on the rear bank, up against the firewall, and that position changes the diagnosis in two ways.

The first is heat: the rear bank gets less air, runs hotter and wears out coils and wiring insulation sooner. The second is practical: reaching those cylinders can require removing the intake manifold, so the part-swap test is no longer free in terms of time, and it pays to plan the order of your checks before you start.

It is worth stopping on a practical point that shapes the whole repair: on many transverse V6 engines the rear bank sits against the firewall and can only be reached by removing the intake manifold, and on some models even by shifting the engine on its mounts.

That changes the strategy completely. On an accessible cylinder, swapping the spark plug and coil is free and takes minutes. Here every teardown costs hours, so it makes sense to spend more time on the tests that do not require taking anything apart: the misfire counter for each cylinder, behavior cold and hot, the fuel trims for that bank and a smoke test. Only once you have that information is it worth opening things up, and then you replace everything that applies in a single job.

P0305 code symptoms

• Check engine light flashing while the misfire is happening.
• Vibration at idle that you can feel in the steering wheel.
• Loss of power and jerking when you accelerate.
• Hard starting and rough idle.
• Smell of unburned gas at the tailpipe.
• Higher fuel consumption.
• The misfire often gets worse with a hot engine because of the temperature of the rear bank.
• Fuel trims off only on the bank that contains this cylinder.

Likely causes of the P0305 code

1. Cylinder 5 coil degraded by heat, common on the rear bank of V engines.
2. Worn spark plug or one with the gap out of specification.
3. Hardened wiring insulation from the heat in that area, with shorts that only appear when hot.
4. Clogged injector or one with an uneven flow.
5. Vacuum leak in the intake runner for that cylinder, frequent on multi-piece plastic manifolds.
6. Low compression from a burned valve or worn rings.
7. Deteriorated head gasket on the rear bank.
8. Injector or coil connector with an intermittent contact from vibration.
9. Deteriorated intake manifold gasket on the rear bank, which creates a localized leak that is hard to find without smoke.
10. Injector with a clogged internal filter, common when the fuel carries dirt.

How to diagnose the P0305 code step by step

1. Identify cylinder 5 in the vehicle documentation. On V engines the numbering varies a lot between manufacturers.
2. Check the misfire counter for each cylinder before you take anything apart. If other cylinders on the same bank are racking up misfires, the cause is shared.
3. Plan the order of your checks. If access means removing the manifold, it makes sense to inspect the spark plug, coil and injector in the same job.
4. Swap the coil with the one from another cylinder and check whether the code moves.
5. Examine the look of the spark plug. Wet with oil points to rings or guides, wet with gas points to a lack of spark, and white points to a lean mixture.
6. Check the wiring insulation in that area, hardened by the heat of the rear bank.
7. Check for vacuum leaks with smoke, paying attention to the gaskets between sections of the manifold.
8. Measure compression if the above does not explain the misfire.
9. Gather as much information as possible before you teardown. On this cylinder every opening costs hours, so use up the tests that do not require disassembly first.
10. Check the fuel trims for the affected bank. A deviation on that side alone points toward an intake leak or injectors.
11. Verify whether access requires removing the manifold and plan the list of parts to replace in the same job.

How to fix the P0305 code

• Replace the whole set of spark plugs while you have things apart, not just the one on the affected cylinder.
• Replace the faulty coil and consider changing the ones on the rear bank if the mileage is high.
• Renew the wiring section with the degraded insulation and protect it with a heat sleeve.
• Clean or replace the injector with insufficient flow.
• Replace the intake manifold gasket if the smoke test confirms the leak.
• Take on the mechanical repair if compression turns out low.
• When access forces you to remove the manifold, plan the whole job in one go: repeating it because only one part was changed multiplies the labor cost.
• Replace the intake manifold gasket while it is apart, even if it is not the main cause.
• Change the spark plugs, coils and injectors on the rear bank in a single job when access is difficult.
• Have the injectors ultrasonically cleaned and renew their internal filters if the fuel carries dirt.

Technical reference data

• Expected compression: 10 to 14 bar (145 to 200 psi), with a maximum difference of 10 percent between cylinders.
• Ignition coil primary resistance: 0.5 to 2 ohms. Secondary: 6,000 to 15,000 ohms.
• Spark plug gap: 0.7 to 1.1 millimeters (0.028 to 0.043 inch), depending on the engine.
• This code only exists on engines with six cylinders or more.
• The rear bank of a transverse V6 runs at a higher temperature and wears out coils and insulation sooner.
• On many transverse V6 engines the rear bank requires removing the intake manifold for access.
• Fuel trims off on only one bank point to a local cause on that side.

Brand-specific notes

On V engines the cylinder numbering varies between manufacturers and does not follow a universal rule. Confirming it before you take anything apart is especially important here, because working on the wrong cylinder of the rear bank can cost hours of labor.

If access means removing the intake manifold, take the chance to check its gaskets: they are a common leak point and the teardown is already done.

Frequently asked questions about P0305