P0301 - Cylinder 1 Misfire Detected

Misfire repair

The repair depends on the cause. The key is to have the problem diagnosed properly. Once you know what caused the engine to misfire, you will know what it needs. Don't start by throwing new parts at it. Even if you planning on doing repairs yourself, it's not a bad idea to have the vehicle properly diagnosed at a dealer or reputable repair facility, where technicians have access to up-to-date information, technical service bulletins (TSB) and advanced scan tool.
The cost of repair will obviously depend on the problem. For example, if the misfire is caused by a bad on-plug ignition coil, which is quite common on many newer cars, the repair might involve replacing a bad coil and all the spark plugs. This could cost $300-$400 for a 4-cylinder engine or $450-$700 for a V6.

Additional trouble codes can shed some light on the cause

Additional OBDII codes that are present along with misfire codes can shed some light on the cause. For example, if you have the P0300 code along with P0171 - System too lean, there is a good chance that the misfire is caused by the lean air/fuel mixture that initially triggered the code P0171. Once the problem caused the code P0171 is fixed, the misfiring will likely go away too. Another example, if you have the code P0401 - EGR insufficient flow along with the P0300, the EGR (Exhaust Gas Recirculation) system needs to be checked first.

What needs to be checked:

- The cause of misfire should be fairly easy to pinpoint if the problem is present all the time. A quick look at the spark plugs can tell a lot. Signs of arcing on ignition coil, distributor cap or rotor can also point to a faulty part. Basics, such as the compression, timing and fuel pressure need to be checked.
- A faulty on-plug ignition coil is typically identified by swapping the coils between the cylinders and checking if the misfire moved with the coil or stayed at the same cylinder. If a bad ignition coil is replaced, it's good idea to change all the spark plugs as well.
- The engine might need to be checked for vacuum leaks. The short term fuel trim (STFT) and long term fuel trim (LTFT) need to be checked with a scan tool to see if the air/fuel mixture is not too lean. Often a bad mass air flow sensor causes the engine to run lean causing misfire. Read more about the STFT and LTFT fuel trims here.
- Pressure testing of the cooling system might be needed to check for a leaking head gasket.
- Valve adjustment may need to be checked, as valves that are out of adjustment can cause misfiring at a cold start, which is, a fairly common issue in Honda engines.
- When the misfiring happens only at idle, the EGR valve and purge valve need to be checked, as either one could be stuck open.
- Faulty mechanical valve train components like worn camshaft lobes or stretched timing chain can also cause the engine to misfire; they too might need to be inspected carefully.
- Sometimes a broken or damaged tooth at the crankshaft or camshaft sensor gear can be the source of misfiring; checking the sensor signal with an oscilloscope can help if crankshaft position sensor (CKP) or camshaft position sensor (CMP) are suspected.
Once the problem is repaired or no longer detected, the misfiring code will clear itself after some driving.

Can a tune-up fix a misfire?

Engine tune up

The term 'tune-up' usually means changing the spark plugs, ignition wires, distributor cap and rotor, and possibly replacing air and fuel filters. Newer cars need a tune-up less frequently, as most modern cars don't have the ignition wires or distributor and use long-lasting spark plugs. If it's been a long time since you had a tune-up done last time, it's a good way to start; at least you will eliminate spark plugs and other tune-up items as a possible cause for misfiring. A tune up needs to be done at least every 60,000 miles anyway. It's best to use only OEM spark plugs and oxygen sensor. Can a tune-up fix a misfire? It really depends on what caused the misfire in the first place. It was because of shorting out ignition wires or old spark plugs, a tune-up will help. If something different caused the engine to misfire, a faulty part needs to be identified first. Read more here »


Q: I have washed the engine compartment and now the engine runs rough; I had it scanned and the code I got is P0303. What could be the problem? It's 1997 Volkswagen Jetta

A: If the car misfires after water got into the engine compartment, most likely it's due to a faulty ignition wires or a coil or because water got inside the distributor. The distributor and other ignition components need to be dried out, for example, with a compressed air. A tune-up with new spark plugs, wires, distributor cap and rotor can help avoid this type of problems in the future.

Q: 3.0L Mazda6 with 110K sputters occasionally, the check engine light is on with the code P0305. What could be the problem?

A: The code P0305 means the cylinder 5 misfires. There could be many reasons for one particular cylinder to misfire. First, check if the spark plugs have ever been changed on this car. With this mileage it's very possible the spark plugs are still original and they could be pretty worn by now. A faulty ignition coil is not uncommon in these engines too. Swapping ignition coils with another cylinder may help to identify a faulty coil. Regardless of the cause, it's a good idea to change all the spark plugs if they are old.

Q: 2002 Mazda Protege drives fine, but runs rough at idle. There are two codes: P0300 and P0401. I've been told it needs a tune up and a new EGR valve, which is quite expensive. What can be done?

A: The EGR valve could be stuck open - it is a common issue on these cars. The new EGR valve for this vehicle has an updated design. If your EGR valve is still original and has never been replaced before, I'd start by replacing it with the new updated OEM part. Then you can decide on a tune up.

Q: What could cause codes P0300, P0301, P0304, P0305 on 2002 Honda Odyssey?

A: There could be a number of possible problems for these codes; read more on previous page. I'd start with checking the valve adjustment; if the valves are too tight, the engine could misfire when cold.

Q: A car was running rough during a rain and the check engine light came on. I checked with my code reader and it was P0300, P0303 and P0304. Should I replace spark plugs and wires? It's the 2.0L motor, 2004 Volkswagen Jetta.

A: Replacing spark plugs and wires is a good idea if it's been a long time since a last tune-up; other than that, there are few other things that can commonly cause misfire on this engine: if the long fuel trim is far in the plus side, more than 15%, the engine could run lean and it also could cause random misfire. The coil pack, if it's old, could also cause misfire during a rain; it's a fairly common problem.