Which bank is cylinder 6 on?

On a V6 it is on bank two, and unusually you can rely on that. Whether the manufacturer alternates the numbering between the banks or numbers down one bank before starting the other, cylinder six lands on the bank that does not contain cylinder one either way. On a straight six there is only one bank, and cylinder six is the last cylinder in the row at the gearbox end.

Why is cylinder 6 harder to fix than the others?

Because of where it sits rather than anything about the fault. On a straight six the rearmost cylinder is under the scuttle at the back of the engine bay, and on several of these engines the inlet manifold or plenum chamber has to be removed before the coil and plug can come out. On a transverse V6 the rear bank is against the bulkhead with the same problem. The part is no dearer than any other coil or plug; the labour to reach it is what changes the bill, which is why it is worth doing the whole set of plugs if the manifold is coming off anyway.

Will a P0306 fail an MOT?

Yes. The illuminated engine malfunction indicator lamp is a major defect for petrol cars first used on or after 1 July 2003 and diesels from 1 July 2008, and it is the largest warning-lamp defect in the DVSA data behind this site with 371,859 recorded failures. A dead cylinder also raises hydrocarbons at the emissions test, which can fail the car a second time.

Powertrain code · standard

P0306Cylinder 6 is misfiring

Standard definition: Cylinder 6 Misfire Detected

Last updated 27 July 2026

Quick answer

Cylinder six is missing combustion events. The useful part is knowing where it is: on a V6 it falls on bank two whichever numbering convention the manufacturer used, and on a straight six it is the cylinder at the bulkhead end, usually the most awkward one on the whole engine to get at.

How the car works this out

The measurement is the standard one — crankshaft deceleration after the firing event, attributed by camshaft position — but cylinder six is a rare case where the position is unambiguous. Whether the manufacturer alternates the numbering between banks or fills one bank before the other, six comes out on bank two on a V6 either way. On a straight six, cylinder six is simply the last in the row at the gearbox end. What varies is not where it is but how much work it takes to reach, and on several straight sixes the inlet manifold or the plenum has to come off before the rearmost coil can be extracted.

What you might notice

A vibration at idle that a straight-six owner in particular notices, because these engines are inherently smooth and any misfire stands out
A change in the exhaust note, often described as a flutter or a beat
Reduced power and a hesitation as you accelerate
The engine management lamp on, flashing if the cylinder is completely dead

What causes it

Most likely first. A code names the check that failed, not the part that failed it, so more than one of these can produce the same number.

1The ignition coil for that cylinderCommon
How to check: Swap it with a coil from a cylinder you can reach without dismantling anything, and see whether the misfire moves with it. Worth doing before committing to the labour of getting at cylinder six properly.
2A spark plug at the end of its life, or one left in place at the last service because reaching it needed the manifold offCommon
3A perished coil boot or oil in the plug well, which is worse at the rear of the engine where heat is trapped under the scuttlePossible
4Harness or connector damage at the back of the engine, the hottest and least inspected part of the loomPossible
5A blocked or failing injectorPossible
6Low compression from a burnt valve, more likely on a high-mileage engine where the rear cylinder runs hottestLess common

What to do about it

1Establish the layout first. On a V6 cylinder six is on bank two whichever way your manufacturer numbers; on a straight six it is the rearmost cylinder against the bulkhead.
2Do all the swap testing you can with parts from accessible cylinders before committing to the labour of reaching the rear one. Proving the coil is faulty from the front of the engine saves stripping the back of it for nothing.
3If the manifold or plenum has to come off anyway, do the whole set of plugs while you are in there. The labour is the expensive part and the plugs are not.
4Check the rear of the loom and the earth points while access is good. They are the parts that never get looked at.

Can you keep driving?

Only to a garage

A six-cylinder engine masks a single misfire well enough that people drive them for weeks. That does not make it harmless: the unburnt fuel is going into the catalytic converter for bank two, and replacing that is a far bigger job than the coil that caused it. Steady lamp, short journey, garage. Flashing lamp, stop.

Will it fail an MOT?

This is the code where the temptation to clear and hope is strongest, because getting at cylinder six can be a real job and the lamp goes out for a while when you wipe the fault. It does not work. Clearing the code resets the on-board readiness monitors, a tester can see they have not completed, and on many cars the emissions check cannot be finished until they have run — which needs a drive cycle of up to a hundred miles. The car then fails on an incomplete emissions test instead of on the lamp, and you have lost the freeze frame data that would have shortened the diagnosis.

The light this turns on

Engine management lightThe engine management system has found a fault it cannot correct and has stored a code for it. The car will usually still drive, but an illuminated engine light is an automatic MOT failure on petrol cars first used from 1 July 2003 and diesels from 1 July 2008.

Common questions

Which bank is cylinder 6 on?: On a V6 it is on bank two, and unusually you can rely on that. Whether the manufacturer alternates the numbering between the banks or numbers down one bank before starting the other, cylinder six lands on the bank that does not contain cylinder one either way. On a straight six there is only one bank, and cylinder six is the last cylinder in the row at the gearbox end.
Why is cylinder 6 harder to fix than the others?: Because of where it sits rather than anything about the fault. On a straight six the rearmost cylinder is under the scuttle at the back of the engine bay, and on several of these engines the inlet manifold or plenum chamber has to be removed before the coil and plug can come out. On a transverse V6 the rear bank is against the bulkhead with the same problem. The part is no dearer than any other coil or plug; the labour to reach it is what changes the bill, which is why it is worth doing the whole set of plugs if the manifold is coming off anyway.
Can I just clear P0306 before the MOT?: No, and it usually backfires. Clearing a code also resets the on-board readiness monitors that prove the emissions systems have self-tested, and a tester can see that they have not completed. On many cars the emissions check cannot be finished until they have run, which takes a drive cycle of up to a hundred miles, so the car fails on an incomplete emissions test rather than on the lamp. If the misfire is still there the lamp will simply come back on within a few miles anyway.
Will a P0306 fail an MOT?: Yes. The illuminated engine malfunction indicator lamp is a major defect for petrol cars first used on or after 1 July 2003 and diesels from 1 July 2008, and it is the largest warning-lamp defect in the DVSA data behind this site with 371,859 recorded failures. A dead cylinder also raises hydrocarbons at the emissions test, which can fail the car a second time.

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