P0301: Cylinder Number 1 Misfire

What is P0301?

The diagnostic trouble code P0301 is defined as the “Cylinder 1 Misfire Detected” fault code.

It is a generic OBD-II trouble code triggered when your vehicle’s PCM (Powertrain Control Module) detects an engine misfire from your first cylinder.

When you have an active P0301 diagnostic trouble code, your vehicle’s Powertrain Control Module has detected a more than 2% increase or decrease in the camshaft’s revolutions per minute. This triggers your check engine light to come on.

If your check engine light is flashing on and off, the percentage increase or decrease in camshaft revolutions per minute is more than 10%.

In short, if you have a misfire in your engine cylinder 1, it reduces your crankshaft’s revolutions per minute, and your PCM will give you the P0301 diagnostic trouble code. 

Every car engine has multiple cylinders, whether you own a  Ford, Toyota, BMW, or Honda motor company vehicle. Cylinder number 1 in misfire code P0301 refers to the first cylinder in the firing order.

For example, V8 engines usually have cylinders numbered 1-4 on the passenger side and 5-8 on the driver’s side. V6s may have them labeled 1-3 on the front bank and 4-6 on the rear bank, depending on your engine design and manufacturer.

Note: The cylinders’ firing order doesn’t necessarily follow the numbering system, so make sure you know which cylinder is first in the firing order. You can consult your car owner’s manual or an online repair manual to find out.

However, P0301 only refers to an engine misfire problem in cylinder 1. Likewise, P0302 refers to a misfire problem in cylinder 2, P0303 to cylinder 3, and so on. 

Common symptoms

You may experience one or more of these common symptoms when your car has an active P0301 code:

• Illuminated or blinking check engine light
• Difficulty starting your car
• Increased emissions 
• A rough idle or jerks while driving
• Reduced engine speed (measured by your camshaft or crankshaft sensor)
• Stalling while stopped
• Lack of power
• Worsened fuel economy

Can I still drive?

If you have an active P0301 code, you should stop driving immediately.

An engine cylinder misfire can lead to an ignition system failure or engine stalling, which is incredibly dangerous.

Furthermore, driving with a misfiring engine could damage other parts of your car, like your catalytic converter. A catalytic converter replacement job is expensive, so fixing the fault code ASAP will save you time and money.

P0301 causes

There are multiple possible causes for the P0301 code and a cylinder misfire, some more common than others.

A. Common Causes Of Code P0301

These are the most common possible causes of a cylinder 1 misfire and code P0301:

• A faulty or damaged spark plug or spark plug wire
• A faulty ignition coil
• Low compression 
• A faulty fuel injector

B. Less Common Causes Of Code P0301

Code P0301 and a misfiring engine are less frequently caused by:

• A faulty oxygen sensor and mass airflow sensor
• A damaged catalytic converter
• Coolant leaking onto the spark plugs
• A faulty PCM
• Broken piston rings or cylinder head valves
• Clogged EGR valves
• A faulty ignition system
• Damaged engine speed sensors like the crankshaft position sensor or camshaft position sensor
• A dirty intake valve
• Low fuel pressure
• A vacuum leak
• A burned exhaust valve
• A leaking head gasket

Diagnosis

Your mechanic will run a series of troubleshooting checks to determine what caused your P0301 code and how to fix the cylinder misfire. 

Mechanics generally start troubleshooting the easiest and cheapest to fix problems before moving on to more complex repairs.

Here’s how your mechanic will diagnose and fix the misfire code:

• They’ll use a scan tool to collect all the error codes and freeze frame data stored by your PCM to see if you just had a random misfire.
• Your mechanic will take your car for a test drive to see if the code returns.
• They’ll check for faulty spark plugs or faulty spark plug wires and replace them if necessary. Replacing old spark plugs with iridium or platinum plugs can also help reduce the misfire rate. 
• Your mechanic will check your ignition coil packs, coil pack wires, and connectors for damage and replace them if required.

Before your mechanic replaces your spark plug and spark plug wire or coil pack and coil pack wire, ask them to inspect your fuel injector wiring. Damaged fuel injector wiring could be causing the engine misfire in cylinder 1, and diagnosing this first could save time.

• Your mechanic will perform a compression test. The compression test checks if your cylinder head valves are causing low compression.
• They’ll check your fuel pump for low fuel pressure.
• If the code persists, your mechanic will check for a faulty fuel injector and replace it if necessary.
• They’ll inspect your distributor cap and rotor button and replace them if they’re defective.
• Fix any other related error codes.
• If all else fails, your mechanic will check your PCM for issues or other error codes as it may require reprogramming or replacing.

Sometimes, there are other overlooked issues including loose-fitting electrical connectors and disconnected vacuum hoses that can trigger code P0301.

Possible repairs for P0301 & Costs

Your mechanic will replace any car part or equipment that has caused the P0301 code, whether it is the spark plugs or spark plug wires, the ignition coil packs and connectors or the fuel injector.

The repair costs depend on the cause of the cylinder misfire.

• New spark plugs: $6-$30 per spark plug
• New ignition coil: $20-$40 per ignition coil
• New spark plug wires: $30-$40
• New fuel injector: $600-$1,200
• New distributor cap: $40-$200
• PCM reprogramming: $80-$150
• New fuel pump: $95-$854
• New PCM: $500-$1,500

Note: The repair costs mentioned above exclude labor charges.