Which cylinder is number 1?

On an inline engine, cylinder one is almost always at the end of the block furthest from the gearbox, which is the end that carries the timing belt or chain and the auxiliary drive. On a transverse installation that puts it at one side of the engine bay rather than at the front. There are exceptions, including some Renault engines that count from the gearbox end, and on V engines nothing can be assumed at all, because cylinder one defines which bank is bank one and manufacturers place it differently. Check the numbering for your specific engine before buying or moving any parts.

How do I know if a P0301 is the coil or the spark plug?

Swap parts one at a time between cylinder one and a neighbouring cylinder and see whether the code moves. Start with the coil, because it is the most likely and the easiest to change. Clear the code, drive the car until the misfire returns, and read the codes again: if it has become a misfire on the cylinder you moved the coil to, the coil is faulty. If it stays on cylinder one after swapping the coil, the plug and the injector, the problem is the cylinder itself and it needs a compression test.

Can I drive with a P0301 code?

Well enough to get to a garage, provided the lamp is steady rather than flashing. Continuing to use the car normally is a poor bet: the unburnt fuel from the dead cylinder passes into the catalytic converter, which is a much bigger repair than the coil or plug that caused it. A flashing lamp means that damage is happening now and the car should be stopped.

Will a P0301 fail the MOT?

Yes. The illuminated engine management lamp is a major defect for petrol cars first used from 1 July 2003 and diesels from 1 July 2008, so the car fails on that alone regardless of how it drives. A misfiring cylinder also raises the hydrocarbon reading at the emissions test, so many cars fail on both counts from the same fault.

Powertrain code · standard

P0301Cylinder 1 is misfiring

Standard definition: Cylinder 1 Misfire Detected

Last updated 27 July 2026

Quick answer

One cylinder, the one the control unit calls number one, is not pulling its weight. When a misfire stays on the same cylinder it almost always means a part belonging to that cylinder: its coil, its plug or its injector, roughly in that order.

How the car works this out

The control unit works out that a cylinder has missed by watching crankshaft speed, not by watching combustion. Each firing event should accelerate the crank by a certain amount; when one does not, the shortfall is measured, and the camshaft signal tells the unit which cylinder was due to fire at that point in the rotation. A per-cylinder counter runs continuously, and P0301 is stored when cylinder one's counter crosses the threshold. This is why a single-cylinder code is so much more useful than P0300: the car has already narrowed the search to one set of parts, and the fastest way to finish the job is to move those parts around and see whether the fault moves with them.

What you might notice

A steady vibration at idle, often described as the car shivering, felt through the gear lever
A rhythmic stumble that keeps the same beat as the engine speed rises
Less power, most obvious pulling away and on hills
The engine management lamp on, and flashing under load if the cylinder is completely dead
A smell of unburnt petrol from the exhaust
Higher fuel consumption, because the fuel going into that cylinder is simply being wasted

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 cylinder, which is the single likeliest answer on any engine with a coil sitting on each plugCommon
How to check: Swap that coil with a neighbouring cylinder's, clear the code and drive it. If the misfire moves to the other cylinder, you have found it. If it stays on cylinder one, the coil is innocent and you have lost nothing but ten minutes.
2A worn, cracked, oil-fouled or wrongly gapped spark plugCommon
How to check: Take it out and lay it next to the others. A plug that is wet, sooty black, oily, or has a visibly wider gap than its neighbours has been telling you for a while.
3Oil in the spark plug well from a leaking cam cover gasket, which soaks the coil boot and lets the spark track to earth before it reaches the plugCommon
How to check: Pull the coil and look down the well. Oil pooled at the bottom is unmistakable, and the rubber boot will be swollen and soft rather than firm.
4A blocked, leaking or electrically dead injector on that cylinderPossible
How to check: Swap the injector with a neighbour the same way as the coil. On port injection this is straightforward; on direct injection it is a much bigger job, so confirm with an injector balance test or a stethoscope on the injector body first.
5A poor connection at the coil or injector plug — a pin pushed back out of the housing, green corrosion, or a chafed wirePossible
How to check: Wiggle the connector and the harness behind it with the engine idling and see whether the running changes.
6Low compression in that cylinder, from a burnt or tight exhaust valve, a broken piston ring or a failed head gasketPossible
How to check: A compression test, then a leak-down test if it reads low. Where the air escapes names the fault: out of the exhaust or the inlet is a valve, into the oil filler is rings, into the coolant header tank is the head gasket.
7Carbon on the back of the inlet valve of a direct injection engine, restricting airflow into that cylinder aloneLess common
8A wiring fault or a failed control unit driver for that coil or injectorLess common

What to do about it

1Establish which cylinder is actually number one before you touch anything. On an inline engine it is almost always at the end furthest from the gearbox, which is the end carrying the timing drive and the auxiliary belt. There are exceptions, including some Renault engines that number from the gearbox end, and on a V engine there is no safe assumption at all. Thirty seconds of checking saves a wasted afternoon.
2Swap the coil with a neighbouring cylinder and see whether the code follows. This is the single most useful thing anyone can do with a single-cylinder misfire and it costs nothing but time.
3If the code follows the coil, replace the coil. If it stays on cylinder one, move on to the plug and then the injector, using the same swap each time.
4If nothing makes it move, stop swapping parts and test the cylinder itself. A misfire that refuses to follow any component is a compression or valve problem, and no amount of new ignition parts will touch it.
5Check the plug well for oil while everything is out. A leaking cam cover gasket destroys coils repeatedly, and fitting a new coil into a well full of oil buys a few months at most.
6If the lamp is flashing rather than steady, stop driving it. One dead cylinder on a four-cylinder engine is a quarter of the fuel going into the catalytic converter unburnt.

Can you keep driving?

Only to a garage

A cylinder misfiring intermittently on a steady lamp will get you to a garage without drama. What you should avoid is carrying on using the car normally, because the fuel that cylinder is not burning ends up in the catalytic converter, and a converter is a far larger bill than a coil. If the lamp flashes, that damage is already happening and the car should be stopped and recovered.

Will it fail an MOT?

The lamp alone fails the test. An illuminated malfunction indicator lamp is a major defect on petrol cars first used on or after 1 July 2003 and diesels from 1 July 2008, and it is the biggest warning-lamp defect in the DVSA data behind this site at 371,859 recorded failures. What surprises people is the second half: one dead cylinder out of four is a quarter of the fuel leaving the engine unburnt, and a car that still drives acceptably can be several times over the hydrocarbon limit at the fast idle test. Get it fixed before the test rather than after, because a retest still needs the lamp out and the readiness monitors run.

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 cylinder is number 1?: On an inline engine, cylinder one is almost always at the end of the block furthest from the gearbox, which is the end that carries the timing belt or chain and the auxiliary drive. On a transverse installation that puts it at one side of the engine bay rather than at the front. There are exceptions, including some Renault engines that count from the gearbox end, and on V engines nothing can be assumed at all, because cylinder one defines which bank is bank one and manufacturers place it differently. Check the numbering for your specific engine before buying or moving any parts.
How do I know if a P0301 is the coil or the spark plug?: Swap parts one at a time between cylinder one and a neighbouring cylinder and see whether the code moves. Start with the coil, because it is the most likely and the easiest to change. Clear the code, drive the car until the misfire returns, and read the codes again: if it has become a misfire on the cylinder you moved the coil to, the coil is faulty. If it stays on cylinder one after swapping the coil, the plug and the injector, the problem is the cylinder itself and it needs a compression test.
Can I drive with a P0301 code?: Well enough to get to a garage, provided the lamp is steady rather than flashing. Continuing to use the car normally is a poor bet: the unburnt fuel from the dead cylinder passes into the catalytic converter, which is a much bigger repair than the coil or plug that caused it. A flashing lamp means that damage is happening now and the car should be stopped.
Will a P0301 fail the MOT?: Yes. The illuminated engine management lamp is a major defect for petrol cars first used from 1 July 2003 and diesels from 1 July 2008, so the car fails on that alone regardless of how it drives. A misfiring cylinder also raises the hydrocarbon reading at the emissions test, so many cars fail on both counts from the same fault.

Check any vehicle's MOT history

Free, instant, and straight from DVSA records. No sign-up.