AutoCodes – Subaru – P0303 Subaru

P0303 Subaru Code - Cylinder 3 Misfire Detected

Quick Answer

When a misfire occurs, engine speed will fluctuate. Common causes include Faulty Spark Plug #3, Clogged or faulty Fuel Injector #3, Faulty Ignition Coil #3. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P0303 Subaru indicates Cylinder 3 Misfire Detected.
Common causes: Common causes include Faulty Spark Plug #3, Clogged or faulty Fuel Injector #3, Faulty Ignition Coil #3.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 58,407

How popular is this code, among other codes? Medium

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Jun 14, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0303 Subaru Description

When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the Crankshaft Position (CKP) sensor signal to vary, the Engine Control Module (ECM) can determine that a misfire is occurring.

OBDII Code P0303 Subaru - Cylinder 3 Misfire Detected - AutoCodes.com — P0303 Subaru Code - Cylinder 3 Misfire Detected

What does this mean?

What are the Possible Causes of the DTC P0303 Subaru?

Faulty Spark Plug #3
Clogged or faulty Fuel Injector #3
Faulty Ignition Coil #3
Fuel Injector #3 harness is open or shorted
Fuel Injector #3 circuit poor electrical connection
Ignition Coil #3 harness is open or shorted
Ignition Coil #3 circuit poor electrical connection
Insufficient cylinder 3 compression
Incorrect fuel pressure
Intake air leak

How to Fix the DTC P0303 Subaru?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

The P0303 code means that the cylinder 3 is misfiring or is randomly misfiring. Start by checking for intake leaks and if no leaks are found the next step is to replace the spark plugs on cylinder 3. If the problem persists more tests needs to be done to diagnose problem, see "Possible Causes"

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0303 Subaru code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0303 Subaru Code

1. What are the common symptoms of an OBDII code P0303 (Cylinder 3 Misfire Detected) in a Subaru?

Symptoms may include engine vibration, rough idle, loss of power, and potentially an illuminated check engine light.

2. What are some possible causes of a P0303 code in a Subaru?

Common causes include faulty spark plugs, ignition coil issues, fuel injector problems, vacuum leaks, or even internal engine issues.

3. How can I diagnose the root cause of a P0303 code in my Subaru?

Diagnosing the issue may involve checking spark plugs, inspecting ignition coils, testing fuel injectors, verifying compression in cylinder 3, and scanning for additional codes.

4. Can driving with a P0303 code in my Subaru cause further damage?

Continuing to drive with a misfire can potentially cause damage to the catalytic converter or other engine components, so it's best to address the issue promptly.

5. Are there any DIY repair tips for fixing a P0303 code in a Subaru?

DIY repair tips may include replacing spark plugs, swapping ignition coils between cylinders to test for issues, checking for vacuum leaks, or using a fuel injector cleaner.

6. How much does it typically cost to repair a P0303 code in a Subaru?

The cost of repair can vary depending on the exact cause of the misfire, but it may range from a relatively inexpensive spark plug replacement to a more costly ignition coil or engine repair.

7. Can a P0303 code be triggered by bad fuel in a Subaru?

While bad fuel quality can potentially lead to misfires, a P0303 code is more commonly associated with specific cylinder-related issues like spark plugs, ignition coils, or fuel delivery problems.

8. Should I clear the P0303 code after fixing the issue in my Subaru?

It's recommended to clear the code after addressing the problem to reset the Check Engine Light and monitor if the issue reoccurs, ensuring the repair was successful.

9. Is it safe to drive my Subaru with a flashing Check Engine Light due to a P0303 code?

A flashing Check Engine Light indicates a severe misfire that can potentially cause damage, so it's best to avoid driving the vehicle and have it inspected by a mechanic promptly.

10. How often should I perform maintenance to prevent a P0303 code in my Subaru?

Regular maintenance, including timely spark plug replacements, ignition system checks, and fuel system inspections, can help prevent issues leading to a P0303 misfire code.