The Engine Fault Code P0303 : Symptoms – Causes and Solutions

The Engine Fault Code P0303 : Symptoms – Causes and Solutions.  Most drivers will encounter engine codes, particularly those with excessive engine miles or engine wear. Furthermore, diagnostic codes might detect serious issues that may necessitate costly repairs. These diagnostic trouble codes, often known as DTCs, can indicate a variety of issues throughout an engine system. Many drivers may encounter the P0303 engine code, but what exactly does it indicate and how serious is the connected problem? We will explore and examine the P0303 engine code, including its symptoms, causes, and the most usually required repairs or treatments, in this article.

The Engine Fault Code P0303 Symptoms - Causes and Solutions

DTC P0303 Definition

P0303 – Misfire in Cylinder 3.

The P0303 code and its meaning are rather simple. When a diagnostic test returns a P0303, it indicates that an engine misfire is occurring, specifically in the engine’s third cylinder. Air, fuel, and a healthy ignition are the three essential necessities for an engine to run. Most engines will misfire if the ignition is faulty or the air-fuel ratio is off. As a result, if you get a P0303 code, your engine is misfiring, notably in the third cylinder. It’s critical to try to diagnose engine misfiring issues as soon as possible to avoid further engine damage or a loss of overall engine efficiency.

In general, if detected immediately, the P0303 code should not be a big source of worry. These are usually minor problems that may be fixed without breaking the bank. If the P0303 code is returned by a diagnostic test without any other codes, the problem is most often caused by carbon or oil-fouled spark plugs. Fortunately, these are neither expensive or time-consuming fixes. However, because P0300 implies several cylinders misfiring, it is likely to occur alongside DTC P0303. For more details on engine misfiring difficulties, see our prior guide on DTC P0300.

P0303 is associated with the following codes:

P0300, P0301, P0302, P0304, P0305, P0306, P0307, and P0308 are the product codes.

Because numerous engine misfires might occur at the same time, these associated cylinder misfire codes may join our mentioned P0303 DTC. As a result, if a diagnostic test reveals a P0301 misfire in the first cylinder, a P0302 misfire in the second cylinder, and so on. Codes will look for each misfiring cylinder related with it.

Symptoms of P0303 Code

The following are some of the symptoms of trouble code P0303:

  • Check engine light/flashing check engine light
  • Engine power loss
  • Poor or erratic acceleration
  • Uneven engine idle
  • Engine performance is subpar.

Due to the sporadic nature of engine misfires, which can occur at regular or irregular intervals, the commonly related symptoms can vary. Regardless, a check engine light is very likely, especially if cylinder one is misfiring. A check engine light or DTC indicating cylinder 1 misfiring may be present in some cases, but this does not rule out the possibility of several cylinders misfiring as well. Additional diagnostics may be required to determine the total number of faulty or misfiring cylinders.

In general, more severe symptoms are more likely to occur with many misfires or in conjunction with other engine system problems. Some of the more serious symptoms include rough acceleration, loss of acceleration and power, a rough idle, and a lack of overall engine performance when driving. Power loss is more likely to be noticeable in engine systems with fewer total cylinders, as each cylinder is more responsible for overall engine power.

DTC P0303: How Serious Is It?

Rating of Severity: Moderate to Severe

Unlike the P0301 code, we grade the P0303 as moderate to severe in terms of overall engine hazard because it can indicate a range of misfiring issues or further engine problems. However, if the P0303 code is only observed in conjunction with the P0300, drivers may be lucky enough to simply have a misfiring third cylinder and an isolated problem. With fewer difficulties comes less expensive repairs and probable engine damage. In contrast to the P0301 code, P0303 is frequently associated with other cylinder misfiring codes. As previously stated, multiple codes can lead to more expensive repairs and greater difficulty determining the source of additional collective engine problems.

As a result, if a P0303 code appears, it is critical to resolve the problem as soon as feasible. Failure to repair a third-cylinder misfire might lead to more serious issues. These additional difficulties can include catalytic converter damage, total ignition failure, and other dangerous hazards to drive with. We will never advise you to drive on a condition that could lead to the full failure of a second or third cylinder. These faults have the potential to cause full engine failure, resulting in accidents and injuries. Again, it is critical that this problem be resolved as soon as possible.

Causes of Engine Code P0303

The following are some of the most prevalent causes of a P0303 DTC:

  • Incorrect ignition components
  • Spark plugs that are faulty or worn out
  • Fuel injector failure
  • Inadequate compression
  • Exhaust valve on fire
  • Oxygen sensor failure

Unfortunately, a P0303 engine code can result from a variety of distinct causes. In comparison to cylinder #1 misfiring, cylinder #3 may have a range of linked faults and hence a variety of catalysts generating these issues. Simply put, a third cylinder misfire can signal a variety of additional engine issues. However, if there are no other connected codes showing on a diagnostic test, it will be considerably easier to pinpoint the source of a P0303 engine code.

Many engine problems, including a third cylinder misfiring, can be avoided with proper maintenance and repairs. Replacing spark plugs and ignition coils can directly prolong an engine’s lifespan and resolve many misfiring issues. Spark plugs must be replaced on a regular basis. However, depending on the engine type and size, these replacement times can vary substantially. Replacement intervals might range from 50,000 to 120,000 kilometres. Turbo engines, on the other hand, are considerably more likely to wear out spark plugs at a much faster pace. Ignition coils, another maintenance item, are also likely to wear out faster in turbo engine systems. However, most ignition coils will need to be replaced every 100,000 to 200,000 miles.

Additional P0303 DTC causes:

It is crucial to highlight that there are numerous additional possible P0303 causes. Other possible causes of a P0303 engine code include:

  • Camshaft sensor failure
  • Crankshaft sensor failure
  • Leak in the hoover
  • Head gasket leak
  • Incorrect engine timing
  • Use of low-quality gasoline

Because the P0303 engine code can indicate a number of major issues, it’s normal for it to have a variety of causes. The cause of this code might vary widely, especially with heavy mileage and wear. This is one another warning to address this problem as soon as possible before diagnosis and fixes grow more complex and expensive. With that said, let’s get started on diagnosing a P0303 code, as well as some of the most typical repairs/solutions for a P0303 DTC in the parts that follow.

Identifying Fault P0303

As previously said, determining the cause of a P0303 engine code in conjunction with other pulled codes will be more challenging than a diagnostic test revealing a single cylinder misfire. As a result, in this diagnostic part, we will only look at situations that result in a single P0303 code. More information on diagnosing engines with multiple DTCs indicating multiple engine misfires may be found here. Moving on, the following are the typical steps used to troubleshoot a P0303 code:

  1. Check for other codes using a diagnostic testing machine. If other DTCs are present, address them first before proceeding.
  2. Check for loose connections or damaged wiring in cylinder #3, as well as loose engine ground wires. Tighten, fix, or reconnect any loose or damaged connections that may be causing engine misfires.
  3. Check the condition of the spark plugs and spark plug wires. Moving the cylinder #3 plug to cylinder #2 and then running the diagnostic test to check whether it returns a P0302 can indicate a defective spark plug. Replace the spark plugs and then check for any existing misfires. The same processes for changing and inspecting components apply to engines that employ individual coil packs rather than spark plug wires.

Finally, let us summarise our P0303 DTC diagnostic steps by providing our final two recommendations for identifying and resolving the misfiring issue.

Related : The Subaru EJ205 Engine Manual

Step 4 of the diagnostic process is to identify fuel system issues.

After completing the previous diagnostic steps and ensuring that your ignition system is operational, the P0303 error may be caused by underlying fuel system faults. As a result, the following two confirmations should be done in order to diagnose a P0303 engine code:

  1. Determine whether there are any current fuel pressure issues. Improper and low fuel pressure can cause engine misfires. Engines receive an incorrect amount of fuel when the fuel pressure is incorrect, resulting in engine misfires. This issue could be caused by a faulty fuel pump or fuel pressure regulator.
  2. Verify that the fuel injectors are working properly. Engine misfires might also be caused by faulty fuel injectors that need to be replaced. Furthermore, ensure that the wiring of the fuel injector is intact, linked, and not damaged.

Engine misfires, including our #3 cylinder misfire, are frequently caused by issues with numerous fuel system components. Now, we’ll go over our final step in diagnosing a P0303 code, as well as some sometimes missed causes.

Checking engine compression and leak-down testing is the fifth diagnostic step.

After ensuring that all fuel system and ignition components are operational, it is time to perform an engine compression and leak-down test. These tests can reveal any other engine issues that may be causing misfires. Among the various issues that can cause a P0303 misfire are:

  • Valve guides that have worn out or a burnt valve
  • Valve spring snapped
  • Piston ring fracture
  • Timing chain that is defective or damaged

Misfires in engines can be caused by a variety of mechanical issues. As a result, checking engine compression and performing a leak-down test to locate any failing mechanical components can be critical. These tests are typically considered the final stage in diagnosing a P0303 misfire, but they can be critical in determining the reason of your engine misfiring problem. Finally, while diagnosing a P0303 engine code or other cylinder misfires, other components such as broken or disconnected vacuum hoses are frequently neglected. It is also critical to ensure that any other electrical connectors are correctly connected or fitted in order to rule them out as potential misfire catalysts.

Now that we’ve determined the source of our P0303 DTC, let’s look at some of the most common and successful fixes for your #3 cylinder misfire in the area below.

The Engine Fault Code P0303 : Symptoms - Causes and Solutions

Repair Costs for P0303 Code

So, now that we’ve determined the source of our P0303 error, the essential question is how much the repair will cost. The prices for our most popular repairs and parts for a #3 cylinder misfire are listed below.

  • Spark plugs range in price from $25 to $300.
  • Spark plug wiring costs between $75 and $300.
  • Ignition coils range in price from $75 to $500 (per).
  • Fuel injectors cost between $1200 and $2000.
  • $1200 to $1900 for a fuel pump
  • Vacuuming a leak costs between $75 and $250.
  • $150-$400 for a fuel pressure regulator

The above-mentioned repair charges will vary due to differences in labour costs and the supply of new parts. However, based on 2022 national averages, we determined these costs to be reasonably accurate. Certain engines with more difficult-to-access components will have higher labour expenses connected with them. Furthermore, certain parts, such as pricy injectors in modern direct injection engines, can be on the more expensive end of the scale.

Regardless of the costs involved, it is critical to address any faults linked with the P0303 DTC owing to the possible hazards it can cause for drivers. We would never advise driving with a P0303 error code.

DTC P0303 Frequently Asked Questions and Summary

In summary, the following is a list of frequently asked questions about the P0303 engine code and their accompanying answers. Some of these responses may be redundant because they are addressed in the sections above. Nonetheless, these condensed responses may provide rapid insight into the various questions surrounding the P0303 DTC.

What Does DTC P0303 Stand For?

The P0303 diagnostic code indicates that engine cylinder #3 is not firing properly. As previously said, if this is the sole code pulled, it is much easier to fully diagnose and repair the problem. However, a #3 cylinder is frequently coupled with other codes and numerous misfiring cylinders.

How Much Do P0303 Code Repairs Cost?

Repair charges for a P0303 can vary substantially due to the multitude of potential problems cited. For example, depending on labour prices and engine type, ignition coil replacements might range from $75 to $500. Furthermore, because it is normal practise to replace spark plugs or ignition coils in pairs, these replacements can be quite pricey. As a result, it may be necessary to obtain a few quotations or estimates (but do not put unnecessary miles on an engine with a P0303 code).

Is Driving Safe With P0303 Present?

No, if a P0303 code is displayed, stop driving immediately and prioritise engine repairs. Because this code can potentially signal faults that cause unexpected engine power loss, it can identify issues that place drivers in dangerous situations and even cause accidents. We will never advise driving on a condition that could result in an accident or injury to any driver.

What Is the Reason for Code P0303?

Finally, there are numerous possible causes for a P0303 engine code. Faulty spark plugs, faulty ignition coils, inadequate compression, and malfunctioning sensors are among the most typical culprits. However, because to the numerous linked difficulties with a #3 cylinder misfire, there are numerous plausible causes. For individuals attempting to identify more causes of a P0303 DTC, please see our further causes section above.