P0301 - Cylinder 1 Misfire Detected

Updated: December 17, 2017

The term misfire means that there is no combustion in one or more cylinders. For example, in this animation, the cylinder 1 misfires and the engine runs only on three cylinders.

Misfiring engine
Cylinder 1 misfires

The engine computer or PCM can detect a misfiring cylinder by monitoring the engine speed. Once misfire is detected, the PCM sets the trouble code and turns on the Check Engine light to alert the driver.

The OBDII trouble code P0301 means that the cylinder number 1 misfires. The code P0302 stands for cylinder 2 misfires, P0303 is the cylinder number 3 and so on.
The code P0300 - random misfire means that multiple engine cylinders misfire at random. The codes P0300-P0308 are called misfire codes.

• Symptoms of a misfiring engine
• Can you drive with misfiring engine?
• What can cause the engine to misfire?
• Common problems
• Misfire repair
• How misfiring is diagnosed
• Additional trouble codes can shed some light on the cause
• Can a tune-up fix a misfire?

Symptoms of a misfiring engine

A misfiring engine shakes, runs unevenly and lacks power. Shaking is more noticeable at idle or when accelerating. The "Check Engine" light on the dash may blink repeatedly or stay on solid. You could also notice the smell of unburned fuel from the exhaust. See this video of a misfiring engine.

Can you drive with the engine that misfires?

Driving with a misfire can damage the catalytic converter, which is an expensive component of the vehicle emission control system. When one of the engine cylinders misfires, unburned gasoline entering the exhaust can overheat and melt the catalytic converter.

Some manufacturers advise not to drive with a misfiring engine; others recommend driving only in a very moderate fashion and, of course, having your vehicle checked out as soon as possible. See your owner's manual for details.

What can cause the engine to misfire:

Fouled spark plug
Fouled spark plug - one of the
common reasons causing misfire

- failed on-plug ignition coil, damaged ignition coil wiring.
- worn-out, cracked or fouled (in the photo) spark plugs
- cracked or shorted ignition wires.
- vacuum leaks. A vacuum leak causes misfire in the cylinder closest to the source of the leak. Examples of vacuum leaks include: leaking intake manifold gasket, broken PCV valve or PCV hose, disconnected vacuum line, cracked vacuum line, ripped intake snorkel
- faulty fuel injector
- damaged engine computer (PCM)
- low fuel pressure
- leaking head gasket
- low compression in the affected cylinder
- valves that are out of adjustment
- bad mass airflow sensor (random misfire).
- stuck open EGR valve or purge valve (solenoid) (random misfire)
- worn valve train components
- improperly set timing
- clogged catalytic converter (random misfire)
- problems with the crankshaft position sensor (CKP) or camshaft position sensor (CMP)
- worn-out, cracked or shorted distributor ignition components: distributor cap, rotor.

Common problems causing misfire:

- Failed on-plug ignition coils are very common reason for misfiring in many cars, including BMW, Ford, Mazda, Nissan, Volkswagen and GM. A failed ignition coil must be replaced. If spark plugs haven't been replaced in a while, it's a good idea to replace all the spark plugs as well. Worn-out spark plugs require higher voltage to produce spark, which adds strain on ignition coils.

- Vacuum leaks, as well as a stuck open EGR valve or purge valve (solenoid) can cause misfire that mostly happens at idle, but goes away at higher rpms.

- In many older cars, washing the engine compartment or driving through deep puddles can cause the engine to misfire, as water gets into the ignition components and shorts them out. A tune-up with new spark plugs and ignition wires usually fixes the problem. On-plug ignition coils that show cracks or signs of arcing need to be replaced too. In older cars with a distributor ignition, a distributor cap and rotor are also replaced as a part of the tune-up.

- In some GM vehicles with V8 engine from late 90's to early 00's, a corrosion at the ECM ground terminal can cause misfiring codes.

- Cracks or corrosion spots on the coils are known to cause misfiring in the rotary engine of Mazda RX-8. Whenever you have a misfire in the Mazda RX-8, coils, spark plugs and spark plug wires are recommended to be replaced first.

- In some older Honda vehicles misfiring can be caused by valves being out of adjustment. Misfiring could be more noticeable when the engine idles after a cold start. As the valve train components wear, the gaps change; to compensate, the valves in many Honda engines need to be adjusted in recommended intervals.

- Sometimes, the engine could misfire if during the timing belt or chain replacement, the timing hasn't been set properly. If the problem started after replacing a timing belt or chain, checking the timing is the first thing to do.

- In many high-mileage cars, oil leaking into a combustion chamber from worn valve seals and oil rings can foul spark plugs causing misfire; often an engine misfires at idle, but runs better after revving up. A blue smoke is another symptom of oil leaking into combustion chambers.

How misfiring is diagnosed

- The cause of misfire should be fairly easy to pinpoint if the problem is present all the time. A quick look at the

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