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AutoCodes – Generic – P0303

P0303 Code - Cylinder 3 Misfire Detected

Quick Answer

The Engine Control Module (ECM) uses information from the crankshaft position sensor and the camshaft position sensor to determine when an engine cylinder misfire is occurring. 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 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 311,963
How popular is this code, among other codes? High
What is this?
Table of contents Created and updated by William Orellana on Jul 21, 2022
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Code P0303 Description

The Engine Control Module (ECM) uses information from the crankshaft position sensor and the camshaft position sensor to determine when an engine cylinder misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM can detect individual cylinder misfire events.
Extreme cylinder misfire events can cause catalytic converter damage. The malfunction indicator lamp (MIL) will flash when the conditions for catalytic converter damage are present. The Diagnostic Trouble Codes (DTC) P0303 correspond to cylinders 3. When the ECM detects that one or more specific cylinders are misfiring, the DTC for the respective misfiring cylinder will set, and up to 2 of the corresponding fuel injectors are disabled for a minimum of 30 s. The ECM will then re-enable the fuel injector and, after approximately 200 engine revolutions, will determine if the misfire is still present. If the misfire is still present, the ECM will disable the fuel injector again repeating the process. If the misfire is not present, the fuel injector will remain enabled by the ECM. In Spark Ignition Direct Injection (SIDI) system applications, if a fuel injector fault DTC is set during a misfire event, the ECM will not re-enable the injector.
OBDII Code P0303 - Cylinder 3 Misfire Detected - AutoCodes.com
P0303 Code - Cylinder 3 Misfire Detected
What does this mean?

What are the Possible Causes of the DTC P0303?

  • 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?

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 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 need to be done to diagnose the problem, see "Possible Causes".













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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0303 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.

Need more information about the P0303 code?

Need more information on how to fix the P0303 code? Get Access to Factory Service Manuals

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Information for Specific Makes

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 Code

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

- Common symptoms include engine rough idling, loss of power, noticeable vibration, and potential engine stalling.

2. What are the typical causes of a cylinder 3 misfire (P0303) error code?

- Causes can include faulty spark plugs, ignition coils, fuel injectors, vacuum leaks, low compression, or issues with the engine control module.

3. How can I diagnose the specific cause of a cylinder 3 misfire indicated by code P0303?

- Diagnosis involves checking spark plugs, ignition coils, fuel injectors, vacuum lines, compression levels, and performing a scan for additional error codes.

4. Are there any simple checks or maintenance tips to address a cylinder 3 misfire (P0303) before seeking professional help?

- You can start by inspecting spark plugs and ignition coils for wear or damage, ensuring proper fuel delivery, and checking for any visible vacuum leaks.

5. Can driving with an unresolved cylinder 3 misfire (P0303) issue cause further damage to the vehicle?

- Continuing to drive with a misfire can potentially lead to damage to the catalytic converter, excessive fuel consumption, and other engine-related problems.

6. What are some possible repair options for addressing a cylinder 3 misfire detected by OBDII code P0303?

- Repairs may involve replacing faulty spark plugs, ignition coils, fuel injectors, repairing vacuum leaks, performing a compression test, or updating the engine control module.

7. How crucial is it to address a cylinder 3 misfire indicated by code P0303 promptly?

- It is important to address a cylinder misfire promptly to prevent potential damage to the engine, ensure optimal performance, and maintain fuel efficiency.

8. Can a cylinder 3 misfire issue be intermittent, causing the OBDII code P0303 to appear sporadically?

- Yes, a misfire in cylinder 3 can be intermittent, leading to sporadic appearances of the P0303 code based on driving conditions and the severity of the issue.

9. Are there any preventative measures to reduce the likelihood of encountering a cylinder 3 misfire and triggering code P0303?

- Regular maintenance, such as timely spark plug replacements, fuel system cleaning, and engine tune-ups, can help prevent cylinder misfires and related error codes.

10. Is it recommended to reset the OBDII code P0303 after addressing a cylinder 3 misfire, or will it clear on its own once the issue is fixed?

- It is advisable to reset the code after addressing the cylinder 3 misfire. However, if the underlying issue is resolved, the code should clear on its own after a few drive cycles.

Discuss the causes and fixes for P0303 OBDII Code

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  • I have replace coil and plugs i have a P0303 code in my navigator what should i do next

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  • Could be a bad injector. What make and model is your vehicle?

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  • I have a 2007 mazda cx7 that was idling Rough, I replaced the spark plugs and it is idling much smoother, but the po303 code keeps displaying. How do I troubled shoot the fuel injectors and ignition coils? I can not find a vacuum leak and the car does not have any less power than normal?

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  • You could try swapping the #3 ignition coil with another coil. If the code follows the coil, then the problem is the coil.

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  • 2010 Chevy Equinox 2.4L 4-Cyl. P0303 code keeps happening (Cyl #3 misfire). So far replaced Cyl #3 coil and all 4 spark plugs. Still getting P0303 code. What can I try next? Or at this point should I get diagnostics from a licensed mechanic?

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  • I have a 2005 infiniti G 35 with a a 3.5 engine. I have a miss fire on my #3 cylinder, I replace all 6 injectors, all 6 plugs all 6 coils, and I did a conpresion test 120'' pounds pressure. I also changed the plug to the injector and the miss is still there. can anyone help

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  • If you already replaced the spark plug and ignition coil, and checked the compression, then the only thing left is the fuel injector. Are there any more codes?

    Before replacing the injector, you could try running some fuel additive, in case the fuel injector is clogged.

    P0303 2005 INFINITI G35 - Number 3 Cylinder Misfire Detected

    Read more: http://www.autocodes.com/p0...

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