Will a P0302 code clear itself?

The code may clear after several drive cycles if the misfire was intermittent and does not recur. However, the underlying cause usually persists, so the code typically returns. Diagnose and repair the fault rather than waiting for it to clear.

How much does it cost to fix a P0302 code?

Repair cost depends on the cause. A spark plug runs $10–30, an ignition coil $50–150, and a fuel injector $100–300. Low compression requiring internal engine work can exceed $1,000. Diagnosis narrows the scope and cost.

Is P0302 the same as P0301?

Both are cylinder misfire codes with the same diagnostic logic, but P0302 refers to cylinder 2 and P0301 to cylinder 1. The causes and repair steps are identical; only the cylinder number changes.

What is the difference between P0302 and P0300?

P0302 indicates a misfire specific to cylinder 2, while P0300 means random or multiple cylinders are misfiring. P0300 often appears with one or more cylinder-specific codes and suggests a broader issue like fuel quality or a vacuum leak.

P0302 Code Meaning: Cylinder 2 Misfire Detected

What P0302 Means

P0302 is the OBD-II diagnostic trouble code for Cylinder 2 Misfire Detected, as defined by SAE J2012. The engine control unit (ECU) sets this code when it detects that cylinder 2 is not firing properly—meaning combustion in that cylinder is incomplete or absent. The ECU monitors crankshaft position and acceleration; when the misfire rate in cylinder 2 exceeds a calibrated threshold over a specified number of revolutions, P0302 is stored and the check engine light illuminates.

This code may appear on its own or alongside P0300 (random/multiple cylinder misfire) or other cylinder-specific misfire codes such as P0301. A flashing check engine light indicates a severe misfire that can damage the catalytic converter and warrants immediate attention.

Symptoms of a P0302 Code

A misfire in cylinder 2 typically produces noticeable drivability symptoms:

Check engine light illuminated (steady or flashing)
Rough idle or vibration, especially at a stoplight
Loss of power or hesitation during acceleration
Increased fuel consumption as the ECU compensates for the misfire
Raw fuel smell from the exhaust, caused by unburned fuel passing through
Rougher running when cold, as misfires are often more pronounced before the engine reaches operating temperature

The severity of symptoms depends on whether the misfire is constant or intermittent and whether other cylinders are also affected.

Common Causes of P0302 (Ranked by Likelihood)

Cylinder 2 misfires stem from one of three systems: ignition, fuel, or mechanical (compression). Based on field data and diagnostic frequency, the most common causes are:

Failed ignition coil on cylinder 2 — Coils degrade over time and are the leading cause of single-cylinder misfires.
Worn or fouled spark plug in cylinder 2 — Plugs wear, gap widens, or carbon deposits prevent proper spark.
Clogged or failed fuel injector for cylinder 2 — Injector may be electrically faulty or mechanically clogged, starving the cylinder of fuel.
Vacuum leak affecting cylinder 2 — A leak in the intake manifold or a cracked hose can lean out the air-fuel mixture for that cylinder.
Low compression in cylinder 2 — Worn piston rings, valves, or a blown head gasket reduce cylinder pressure and prevent complete combustion.
Wiring or connector issues — Damaged wiring or corroded connectors to the coil or injector can interrupt signal or power.
Carbon buildup on intake valves — Common in direct-injection engines, carbon deposits restrict airflow and disrupt combustion.

How to Diagnose P0302

The diagnostic path for P0302 follows a logical sequence of component swaps and tests to isolate the fault. Start with the most common and easiest-to-test components before moving to mechanical causes.

Read Freeze-Frame Data

Capture the freeze-frame snapshot stored with the code. Note engine speed, load, coolant temperature, and fuel trim values at the moment the misfire was detected. This context helps identify whether the misfire occurs under specific conditions (cold start, idle, acceleration).

Swap the Ignition Coil

Move the ignition coil from cylinder 2 to another cylinder (for example, cylinder 4). Clear the code, drive the vehicle, and scan again. If the misfire code changes to the new cylinder (P0304 in this example), the coil is faulty. If P0302 remains, the coil is not the cause.

Swap the Spark Plug

Remove the spark plug from cylinder 2 and swap it with a plug from another cylinder. Clear codes and retest. If the misfire follows the plug to the new cylinder, replace the plug. If P0302 persists, the plug is not at fault.

Test the Fuel Injector

Check the injector's electrical resistance with a multimeter and compare to specification. Listen for injector clicking with a mechanic's stethoscope or use a scanner that analyzes live data to monitor injector pulse width. If available, swap the injector with one from another cylinder and retest. A clogged or failed injector will cause the misfire to follow.

Perform a Compression Test

If ignition and fuel components test good, perform a compression test on cylinder 2. Low compression (significantly below specification or compared to other cylinders) indicates worn piston rings, valves, or a head gasket leak. Compression testing and internal engine repairs warrant a qualified mechanic.

Inspect for Vacuum Leaks

Visually inspect vacuum hoses, the intake manifold gasket, and any connections near cylinder 2. Spray carburetor cleaner around suspected leak points while the engine idles; a change in idle speed indicates a leak. Repair or replace damaged hoses and gaskets.

Check Wiring and Connectors

Inspect the wiring harness and connectors to the ignition coil and fuel injector for cylinder 2. Look for frayed wires, corrosion, or loose pins. Repair or replace damaged wiring.

Repair and Next Steps

Once you've identified the faulty component through swap testing or measurement, replace it:

Ignition coil: Replace the coil for cylinder 2. Consider replacing all coils if the vehicle has high mileage and original coils.
Spark plug: Replace the plug for cylinder 2, or replace all plugs as a set if they are near the end of their service interval.
Fuel injector: Replace or clean the injector. Some injectors can be ultrasonically cleaned; others must be replaced.
Vacuum leak: Replace the damaged hose or intake manifold gasket.
Wiring: Repair or replace the damaged section of the harness.

If compression is low, consult a qualified mechanic. Internal engine work—such as valve replacement, piston ring replacement, or head gasket repair—requires specialized tools and expertise.

After the repair, clear the code with a scan tool and perform a test drive under the conditions noted in the freeze-frame data. Monitor the vehicle for code recurrence. If P0302 returns, revisit the diagnostic steps or seek professional assistance.

Diagnostic output is a decision-support estimate, not a substitute for professional inspection.

P0302 Code: Cylinder 2 Misfire Detected