Engine Fault Code P0303 – Symptoms, Causes, Fix

Engine codes are bound to pop up for most drivers, especially those with high engine mileage or engine wear. Furthermore, diagnostic codes can identify severe problems that can lead to costly repairs. These diagnostic trouble codes, also known as DTCs, can showcase a range of different problems throughout an engine system. Many drivers might run into the P0303 engine code, yet what does it really mean and how serious is the associated problem? Within this guide, we will discuss and examine the P0303 engine code including its symptoms, causes, and most commonly required repairs or solutions.

P0303 Spark Plug

DTC P0303 Meaning

P0303 – Cylinder 3 misfire detected.

The P0303 code and its meaning are pretty straightforward. When a diagnostic test pulls a P0303 an engine misfiring problem is occurring, specifically within the engine’s third cylinder. Three basic requirements for an engine to function are air, fuel, and a healthy ignition. With a defective ignition or an improper balance of air and fuel, most engines will misfire. Therefore, if a P0303 code is present then your engine is misfiring, specifically within the third cylinder. It’s essential to try and identify engine misfiring issues in a timely manner to prevent further engine damage or lack of overall engine efficiency.

Generally, if identified quickly, the P0303 code shouldn’t be a major cause for concern. These are usually common minor issues that can be repaired without breaking the bank. If the P0303 code is pulled with a diagnostic test, without accompanying codes, then the issue is likely related to carbon or oil-fouled spark plugs. Thankfully, these are not extremely pricey or time-consuming repairs. However, fault code P0300 is likely to occur alongside DTC P0303 as P0300 indicates multiple cylinders misfiring. Check out our previous guide on DTC P0300 for further information on engine misfiring issues.

More Associated Codes with P0303

P0300, P0301, P0302, P0304, P0305, P0306, P0307, and P0308

Due to the fact that many times multiple engine misfires may occur, these associated cylinder misfire codes may accompany our mentioned P0303 DTC. Therefore if a diagnostic test shows a P0301 a misfire has occurred in the first cylinder, P0302 shows a misfire in the second cylinder, and so on. Codes will pull for each associated cylinder that is misfiring.

Code P0303 Symptoms

Some of the various symptoms of fault code P0303 are as follows:

  • Check engine light/check engine light flashing
  • Loss of engine power
  • Poor or rough acceleration
  • Rough engine idle
  • Poor engine performance

Due to the sporadic nature of engine misfires, they may occur consistently or at less consistent intervals, the generally associated symptoms can vary. Regardless, a check engine light is most likely to occur especially if cylinder one happens to be misfiring. In certain instances a check engine light or DTC indicating cylinder 1 misfiring may solely be present, however, this does not necessarily dismiss the chance of multiple cylinders misfiring as well. Further diagnostics may be needed to specify the total amount of cylinders that are defective or misfiring.

Generally speaking, more severe symptoms are more likely to occur with multiple misfires or in conjunction with other problems within the engine system. Some of these more serious symptoms ranging from rough acceleration or loss of acceleration and power to a rough idle or even lack of overall engine performance as previously experienced while driving. Loss of power is more likely to stand out in engine systems that have a smaller amount of total cylinders, as each cylinder is more responsible for overall engine power.

How Serious Is DTC P0303?

Severity Rating: Moderate to Severe

Unlike the P0301 code, we rate the P0303 as moderate to severe in terms of overall engine danger, due to the fact that it may represent a variety of misfiring problems or further engine issues. However, if the P0303 code is found solely along with the P0300 then drivers may be fortunate enough to only have a 3rd cylinder misfiring and an isolated problem. With fewer associated problems come less pricey repairs and potential engine damage. In comparison to the P0301 code, P0303 will often pop up alongside other cylinder misfiring codes. As we said, multiple codes can add up to more expensive repairs and more difficulty identifying a source of other collective engine problems.

Therefore, if a P0303 code pops up it’s imperative to fix the issue as soon as possible. Failure to fix a 3rd cylinder misfire can lead to further and more severe problems. These further problems can include catalytic converter damage, total ignition failure, and other hazardous issues to continue driving with. We will never recommend driving on a problem that can result in the complete failure of a second or third cylinder. These issues can potentially lead to complete unexpected engine failure leading to accidents and injury. Again, it is absolutely imperative to fix this issue immediately.

Engine Code P0303 Causes

Some of the most common causes for a P0303 DTC include:

  • Faulty ignition components
  • Faulty/worn out spark plugs
  • Defective fuel injector
  • Poor compression
  • Burned exhaust valve
  • Faulty oxygen sensor

Unfortunately, there is a multitude of different causes that can produce a P0303 engine code. In comparison to cylinder #1 misfiring, cylinder #3 can have a variety of different associated issues and therefore a variety of different catalysts causing said issues. Simply put, a third cylinder misfire can indicate many other engine problems. Again though, it will be much easier to identify the cause of a P0303 engine code if there are no other associated codes pulling upon a diagnostic test.

Proper maintenance and repairs can deter many engine issues, including a third cylinder misfiring. Replacing spark plugs and ignition coils can directly extend the lifespan of an engine and absolve many engine misfiring issues. Spark plugs require intermittent replacement. However, these replacement times can vary greatly on engine type and size. Average replacement times can range from every 50,000 to 120,000 miles. Yet, turbo engines are much more likely to wear through spark plugs at a much faster rate. Ignition coils, another maintenance requirement, are also likely to be worn more quickly in turbo engine systems. However, most ignition coils will need regular replacement between 100,000 and 200,000 miles.

Further P0303 DTC causes:

It is important to note that there are plentiful other potential causes P0303 causes. Various other causes for a P0303 engine code can include:

  • Defective camshaft sensor
  • Defective crankshaft sensor
  • Vacuum leak
  • Leaking head gasket
  • Improper engine timing
  • Usage of poor quality fuel

Since the P0303 engine code can be indicative of a variety of serious problems, it’s natural for it to also have a variety of different causes. This code’s cause can range greatly, especially over high mileage and wear. Again, this is another reminder to fix this issue as soon as possible before diagnosis and repairs become more difficult and costly. With that said, let’s jump into diagnosing a P0303 code, as well as some of the most common repairs/solutions for a P0303 DTC within the next following sections.

Diagnosing Fault P0303

As mentioned previously, identifying the cause for a P0303 engine code alongside other pulled codes will be more difficult than a diagnostic test showing a singular cylinder misfire. Therefore within this diagnostic section, we will focus solely on circumstances that produce a singular P0303 code. For more information on diagnosing engines producing multiple DTCs indicating multiple engine misfires, please reference our previous article on the P0300 engine code. Moving along, listed below are the common steps that are taken to diagnose a P0303 code:

  1. Use a diagnostic testing machine to check if other codes are present. If other DTCs are present, address them first before moving forward.
  2. Confirm that there are no loose connections or damaged wiring for cylinder #3, also check for loose engine ground wires. Tighten, repair, or re-connect any loose connections or faulty wiring that may be the cause of engine misfires.
  3. Confirm that the spark plugs and spark plug wires are in good condition. Testing spark plugs by moving the cylinder #3 plug to cylinder #2, then seeing if the diagnostic test produces a P0302 can indicate a faulty spark plug. Therefore, replace spark plugs and then check again for any present misfires. The same steps of replacing and checking components can be applied to engines that use individual coil packs as opposed to spark plug wires.

Finally lets sum up our P0303 DTC diagnostic steps with our last two recommendations to identify and resolve the misfiring issue.

Diagnostic Step #4: Identifying fuel system problems

Once the previous diagnostic steps have been completed, and after confirming that your ignition system is working properly, the P0303 code may be caused due to underlying fuel system issues. Therefore, the following next two confirmations should be made to diagnose a P0303 engine code:

  1. Identify if there are present issues with fuel pressure. Improper and low fuel pressure can directly result in engine misfires. With improper fuel pressure, engines receive an improper amount of fuel creating engine misfires. This specific problem can be the product of a defective fuel pump or fuel pressure regulator.
  2. Confirm that fuel injectors are properly functioning. Engine misfires can also be a direct product of defective fuel injectors needing replacement. Furthermore, confirm that the fuel injector’s wiring is intact, connected, and not damaged.

Problems within various fuel system components are common causes of engine misfires, including our #3 cylinder misfire. Now, let’s discuss our final step in diagnosing a P0303 code below, as well as some commonly overlooked causes.

Diagnostic Step #5: Checking engine compression and leak-down testing

After confirming that all fuel system and ignition components are functioning properly, its time to conduct an engine compression test and leak-down test. These tests can highlight any further engine problems that can produce misfires. These varying problems that can result in P0303 misfire include:

  • Worn valve guides or burned valve
  • Broken valve spring
  • Broken piston ring
  • Defective or broken timing chain

Multiple mechanical problems can cause engine misfires. Therefore, it can be essential to check engine compression and perform a leak-down test to identify any malfunctioning mechanical components. These tests are usually considered the last step when diagnosing a P0303 misfire, however, can be the key to finding the cause of your engine misfiring problem. Lastly, other components such as broken or disconnected vacuum hoses are often overlooked when diagnosing a P0303 engine code or other cylinder misfires. It is also imperative to confirm that any other various electrical connectors are connected or fitting properly to rule them out as potential misfire catalysts.

Now that we have diagnosed the cause of our P0303 DTC, let’s examine some of the most common and effective repairs for your #3 cylinder misfire in the following section.

P0303 Code Repair Costs

So we’ve diagnosed the root cause of our P0303 code, now the crucial question is, how much will the repair cost? Following is a price list of our most common repairs and parts for a #3 cylinder misfire.

  • Spark plugs: $25 – $300
  • Spark plug wiring: $75 – $300
  • Ignition coils: $75 – $500 (each)
  • Fuel injectors: $1200 – $2000
  • Fuel pump: $1200 – $1900
  • Vacuum leak: $75 – $250
  • Fuel pressure regulator: $150 – $400

The repair prices listed above will vary due to differentiating labor costs and the source of replacement parts. However, we found these prices to be accurate enough based on the 2022 national averages. Certain engines with more difficult-to-access components will have higher associated labor costs. Also, certain parts can sit on the more expensive side of the spectrum due, such as pricey injectors in modern direct injection engines.

Regardless of the associated costs, it is absolutely essential to repair any issues associated with the P0303 DTC due to the potential hazards it can create for drivers. We would never recommend driving on a P0303 fault code.

DTC P0303 FAQs & Summary

In summation, below are a list of common FAQs for the P0303 engine code and their associated answers. Some of these answers may be redundant in that they are answered within the sections above. Yet, these summarized answers may offer quick insight into the many questions surrounding the P0303 DTC.

What Does DTC P0303 Mean?

The P0303 diagnostic code means that engine cylinder #3 is misfiring. Like we said previously, this issue is much easier to diagnose properly and repair if it is the only code pulled. However, a #3 cylinder is quite commonly associated with other codes and multiple other cylinders misfiring. Feel free to reference our previous guide on engine code P0300 if experiencing multiple codes and multiple engine misfires. Also, if experiencing a #1 cylinder misfire, our P0301 engine code guide will also be helpful!

How Costly Are P0303 Code Repairs?

Due to the variety of our listed potential causes, repair costs for a P0303 can vary greatly. For example, ignition coil replacements can range from $75 – $500 depending on labor costs and engine type. Also, since it is commonly recommended to replace spark plugs or ignition coils in sets, these replacements can range on the costly end of the spectrum. Therefore, it may be important to get a few quotes or estimates (however, do not put unneeded excessive miles on an engine pulling a P0303 code.)

Is It Safe To Drive With P0303 Present?

No, if a P0303 code is present stop driving immediately and prioritize completing engine repairs immediately. Due to the fact that this code can potentially indicate problems that result in sudden engine power loss, the P0303 can identify issues that put drivers into hazardous conditions and even cause accidents. We will never recommend driving on a problem that can cause accidents and injury to any driver.

What Is The Cause of Code P0303?

Finally, there are multiple different potential causes for a P0303 engine code. However, some of the most common causes include faulty spark plugs, defective ignition coils, poor compression, and faulty sensors. Yet, due to the many different associated problems with a #3 cylinder misfire, there are many varying potential causes. Feel free to reference our further causes above for those trying to identify further causes of a P0303 DTC.

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