Diagnostic Trouble Code (DTC): P0301
P0301 Code Definition.
A misfire was detected on cylinder 1.
What code P0301 means
In most vehicles, there are 4-6 cylinders. In order, each cylinder fires the spark plug smoothly and steadily. The spark plug ignites the fuel using a flammable mixture of fuel and air. The crankshaft is driven by the energy released by the fuel.
The cylinders control the revolutions per minute (RPM) of the crankshaft. All the cylinders work together to ensure that the crankshaft continues to rotate. If one of the cylinders fails, the RPM of the crankshaft increases or decreases.
If the powertrain control module detects that there is an increase or decrease in crankshaft RPM per minute of more than 2%, it will record fault code P0301.
The Check Engine light will come on when the percentage increase or decrease in crankshaft revolutions per minute is between 2 and 10 percent. The Check Engine indicator light will illuminate when the percentage of increase or decrease in crankshaft revolutions per minute is greater than 10 percent.
A percentage increase or decrease in crankshaft revolutions per minute greater than 10 percent indicates that the misfire problem is more serious. Fault code P0301 indicates that cylinder 1 is not receiving the necessary spark, resulting in an ignition fault condition.
What causes the P0301 code?
- Faulty spark plug in cylinder 1.
- No compression in cylinder 1
- Damaged or excessively worn spark plug wires and/or coils.
- Damaged or excessively worn distributor cap (not applicable to all vehicles).
- Damage or excessive wear to the rotor knob (not applicable to all vehicles).
- Defective fuel injector
- Blocked valves or EGR lines
- Burnt valves
- Inaccurate ignition timing
- Vacuum leaks
- Low fuel level (rare)
- Cylinder head gasket leakage
- Cracked distributor cap
- Camshaft sensor defective
- Crankshaft sensor defective
- Air mass sensor faulty
- Defective oxygen sensor
- Defective throttle position sensor
- Defective catalytic converter
- Traction unit control module defective
What are the symptoms of the P0301 code?
- The check engine light comes on or blinks
- The vehicle is difficult to start or does not start at all.
- The vehicle hesitates or limps when accelerating.
- Vehicle engine runs incorrectly
- Vehicle runs at idle speed
- Power failure while the vehicle is running
- Vehicle stops or shuts down while stopped
- The vehicle has increased fuel consumption.
How can a mechanic diagnose the P0301 code?
- Use the OBD-II scanner to collect all the fault codes and freeze the frame data stored by the powertrain control module.
- Test the vehicle to see if the P0301 code has reappeared.
- Check spark plug wire for damage or excessive wear on cylinder 1.
- Check the spark plug cylinder itself for damage or excessive wear.
- Check the coil packs for damage or excessive wear
- Inspects coil wires for damage or excessive wear
- Replace spark plugs, spark plug wires, coil packs, and coil pack leads as necessary.
- After replacing these components, if the P0301 error code returns, you may need to check the fuel injectors and fuel injector wires to see if they are damaged in any way.
- Check the distributor cap and/or rotor button for corrosion and/or cracks (older vehicles have a distributor cap and rotor button system – this step does not apply to all vehicles).
- Diagnose and repair any other codes recorded by the powertrain control module that are related to fault code P0301.
- Repeat the test drive to see if the P0301 trouble code reappears.
- After the test drive, if the P0301 trouble code returns, check the cylinder 1 compression system (this happens rarely).
- There may be a problem with the powertrain control module if trouble code P0301 persists. This happens rarely, but may require replacement or reprogramming.
Frequent errors when diagnosing the P0301 code
Before replacing spark plugs, spark plug wires, coils, and coil wires, visually inspect the fuel injector wires for damage.
While it is rare that damaged fuel injectors are the problem, performing a quick visual inspection can save some time. Exclude the possibility that a defective cylinder is the cause of the problem.
It is also important to complete the diagnosis and necessary repairs of other related fault codes that have been recorded by the powertrain control module. Any of these may be the cause of the ignition problem.
How serious is the P0301 code?
Error code P0301 is considered serious because of the driving problems that occur when this error code is stored by the powertrain control module. Driving can be dangerous if the car accidentally stalls or stops while driving. Error code P0301 should be cleared as soon as possible.
What repairs can fix the P0301 code?
- Replacement of defective spark plugs
- Replacement of defective spark plug wires and/or coils.
- Repair or replacement of clogged EGR valves and/or clogged EGR hoses.
- Replace blown valves
- Repair vacuum leaks
- Repair or replace leaking cylinder head gaskets
- Defective camshaft sensor Replacement of camshaft sensor
- Replace damaged crankshaft sensor
- Replace defective air mass flow sensor
- Replacing a defective oxygen sensor
- Replacement of a defective throttle position sensor
- Replacement of defective fuel injectors
- Replacing the damaged catalytic converter
- Diagnose other related fault codes and repair as necessary
- Replace distributor cap and rotor knob, as well as wires, coils, and spark plugs
- Make necessary repairs to the internal engine components.
- If the cylinders are damaged, the engine may need to be replaced.
- Although rare, you may need to replace or reprogram the powertrain control module.
Additional notes to consider code P0301
A quick way to determine if the misfire problem is the result of a faulty wire or coil pack is to replace the wire and/or coil pack with another wire and/or coil pack. If the trouble code for another cylinder returns, this is a good indication that the wire and/or coil pack is the cause of the misfire.
It is important to replace all spark plugs when repairing a misfire code. If only the spark plug for the affected cylinder is replaced, other cylinders may fail. If other related codes are stored in the powertrain control module, check and diagnose them.
It is also important to make sure that the spark plugs have the correct spacing. Failure to do so can result in misfiring. Spark plugs should be slotted according to the manufacturer’s specifications. These specifications can be found on a sticker under the hood of the vehicle. Any local auto parts store will also have gap specifications. Use a gap gauge to space the spark plugs correctly.
