P0301 - Cylinder 1 Misfire Detected

Updated: September 30, 2013
Misfiring engine
Cylinder 1 misfires

The term engine misfires means that there is no combustion in one or more of the engine cylinders. If the engine misfires at certain conditions but not all the time, it's called intermittent misfire. 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
• What needs to be checked
• Additional trouble codes can shed some light on the cause
• Can a tune-up fix a misfire?
• Questions and answers

Symptoms of a misfiring engine

When misfiring, the engine will shake and run unevenly. This is especially noticeable at idle or when accelerating from a stop. A car will lack power and the "Check Engine" light on the dash may blink repeatedly or stay on solid. You could also notice smell of unburned fuel from the exhaust.

Can you drive with the misfiring engine?

Driving with misfiring engine 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. If the ECM detects that the misfire rate is high enough to damage the catalytic converter, the Check Engine light will start blinking on the instrument panel. Some manufacturers advise not to drive with a misfiring engine; others recommend driving only in a very moderate fashion and, of course, have 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

- problems with the ignition components: spark plugs, ignition wires, coils, distributor, ignition module.
- fouled spark plugs
- faulty fuel injectors
- lean air/fuel mixture due to bad airflow sensor, vacuum leaks, etc.
- vacuum leaks; examples: cracked vacuum hose, disconnected vacuum line, cracked vacuum line, cracked intake snorkel
- low fuel pressure
- leaking cylinder head gasket
- low compression
- valves are out of adjustment
- worn valve train components
- improperly set timing
- Stuck open EGR valve or purge valve (solenoid)
- clogged exhaust
- problems with the crankshaft position sensor (CKP) or camshaft position sensor (CMP)

Common problems causing misfire:

- In some Honda vehicles the misfiring often 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.
- A technical service bulletin (TSB) for some Buick Rainier, Chevrolet Trailblazer, GMC Envoy and other models with a 4.2L in-line 6 cylinder engine describes a condition where the codes from P0300 to P0306 could be set after a heavy rain, especially if the vehicle is parked nose down on an incline, as the dripping water can collect on the ignition coils and spark plugs. As a solution, the bulletin recommends checking and replacing the ignition components if needed, as well as installing a revised seal for the engine compartment.
- In many older cars, especially if a tune-up hasn't been done for a while, washing the engine compartment or driving through a rain can cause the engine to misfire, as water might get into the ignition components and short them out. The fix usually involves a tune up with new spark plugs, wires, distributor cap and rotor.
- 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.
- In early 00's Nissan Sentra, a bad cylinder head gasket could cause the engine to misfire. A head gasket is quite expensive to replace.
- In many older cars, worn and cracked ignition wires often cause misfire; the longer the ignition wire, the more chances the spark will jump off the wire. The solution again is a tune up.
- Faulty on-plug ignition coils are very common reason for misfiring in some Ford, Mazda, Nissan, Volkswagen and other cars.
- 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 many high-mileage cars, oil leaking into a combustion chamber from worn valve seals can foul the spark plugs causing misfire; often this happens after the engine runs at idle for a while. If this issue is suspected, spark plugs need to be checked for oil contamination.
- Vacuum leaks, as well as a stuck open EGR valve or purge valve (solenoid) can cause misfire that mostly happens at idle.
- 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 usually the first thing to do.