Engine Fault Code P0300 – Symptoms, Causes, Fix
Engine fault codes are simply a part of car ownership. If you own cars long enough something is bound to go wrong at some point. Code P0300 is among the most common diagnostic trouble codes (DTC). In this guide, we discuss the meaning, symptoms, causes, fixes, and more for fault code P0300.
DTC P0300 Meaning
P0300 – Random/Multiple cylinder misfire detected
This fault code indicates at least two cylinders are misfiring. A misfire occurs when a cylinder fails to achieve full ignition/combustion. Air, fuel, and ignition are the three primary keys for an internal combustion engine. Without the proper ratios an engine will experience misfires and run poorly.
It’s usually a pretty minor, inexpensive issue that causes DTC P0300. However, it can be one of the harder problems to diagnose since there are a lot of potential symptoms and causes. Worry not, though. We dive into all of this info and provide helpful steps to successfully diagnose and repair P0300 fault code problems.
Common Codes With P0300
P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308
The above fault codes are essentially the same, but represent misfires on its respective cylinder. Below is an example:
- P0301 – Cylinder 1 misfire detected
- P0302 – Cylinder 2 misfire detected
So on so forth. It’s very likely you receive a couple of these fault codes alongside P0300. If multiple cylinders are misfiring the engines control unit should also be putting out fault codes for the specific cylinders misfiring. More on all of these DTC’s when we discuss symptoms, diagnostics, etc.
Code P0300 Symptoms
Symptoms that come with fault code P0300 can be a nearly endless list. As such, the below isn’t a completely exhaustive list of possible symptoms. Nonetheless, look for the following P0300 symptoms:
- Check engine light
- Flashing check engine light
- Rough idle
- Stuttering / hesitation accelerating
- Power loss
- Poor overall performance
Exact symptoms can vary a lot on a case by case basis. How many cylinders are misfiring? How often are the misfires occurring? What’s the underlying cause that’s responsible for triggering the misfires? These are all factors that tie into the severity of symptoms from fault code P0300.
A check engine light should be present. It may also flash which usually indicates more severe misfires. Again, P0300 misfires mean some cylinders aren’t reaching a complete air-fuel burn. Misfires often result in rough idle, stuttering, power loss, and poor overall performance.
If only two cylinders are misfiring occasionally on a V8 engine then symptoms will be less noticeable. On the other hand, two cylinders misfiring often on a 4-cylinder engine will result in more dramatic symptoms with DTC P0300.
How Serious Is DTC P0300?
Severity Rating: Moderate
We ran into a few similar articles that list this issue as serious/severe. No offense but we cannot disagree with that more. Usually P0300 is very low severity. It’s not like a water pump failure that puts the engine at high risk of overheating severely. It’s not a loss of oil pressure. These are issues that put the engine in danger and can cause complete engine failure or other costly problems.
More often than not P0300 is a low severity engine fault code. We’ll be moving onto this in the causes section next, but among the most common are spark plugs and ignition coils. They’re wear and tear parts that go bad with age. Tons of engines and drivers run into P0300 and other misfire codes on a daily basis.
That said, we’re sticking with a moderate rating instead of low severity for good reason. It is possible that misfires are drastic enough to cause drivability issues. Use your own judgement. If anything feels dangerous then play it on the safe side. You still want to diagnose and repair P0300 faults as soon as possible. However, it’s rarely an issue that should cause the need to pull over and tow the vehicle home.
Engine Code P0300 Causes
The most common causes of engine fault code P0300 include:
- Spark plugs
- Ignition coils / distributor
- Fuel injectors
- Fuel delivery issues
- Vacuum leaks
- Cam or crank sensors
Spark plugs and ignition coils are by far the most common causes of misfires codes. However, P0300 specifically is a bit less common than if you get a single P0301, P0302, etc code. Why? Plugs and coils are wear and tear parts that are standard maintenance. They don’t always wear at the exact same rate in every single cylinder.
It’s not easy to sum this up in words, but here’s what we’re trying to say. Single cylinder misfires are almost always a single spark plug, ignition coil, or fuel injector. These are still the most common causes of P0300 multiple cylinder misfire codes. However, multiple misfires also leaves more room for other possibilities. Hopefully the next paragraph helps sum this up, too.
If you’re having fuel delivery issues this affects multiple cylinders. Most engines have 1 fuel pump feeding all cylinders. As such, a bad fuel pump, sensor, rail, line etc affects all cylinders and can cause multiple misfires. A cam sensor affects all cylinders that specific camshaft sensor is responsible for. A crankshaft sensor affects all cylinders. As such, these are all common causes of P0300 fault codes.
Less Frequent Causes
Some other less common problems that may cause P0300 are as follows:
- Bad fuel
- Ignition timing off
- Low compression
Running into bad fuel quality doesn’t happen too often, but it’s possible. Poor fuel might not ignite properly and lead to misfires (usually on all or most cylinders). Ignition timing off usually means the timing belt or chain snapped or jumped a few teeth. It’s a serious issue when this occurs and you’ll likely notice very severe symptoms and drivability issues.
Otherwise, as engines age they can begin losing compression (or if a failure occurs). Loss of compression is a serious internal engine problem. It’s not something you want to run into, but it’s probably the least common cause of diagnostic trouble code P0300.
Diagnosing Fault P0300
P0300 is a very rare code to receive by itself. If the control unit is reading everything correctly there should almost always be other codes present. This makes diagnosing DTC P0300 a bit easier. It also makes it a bit more challenging for us to run through the many different scenarios.
Below is a way to diagnose code P0300 assuming other single cylinder misfire codes are present:
- Confirm code P0300 and individual misfires codes are present
- Delete codes with scanner and test drive. If no codes are present then repeat this cycle to confirm. Otherwise, if the codes come back then it’s time to track down the actual issue
- Double check to confirm the individual cylinders that are misfiring
- Visually inspect ignition coil wires and other easily visible sensors, hoses, lines, etc
- If nothing seems out of place then it’s time to move onto some dirty work that’s pretty straight-forward for even novice car owners
- Swap the ignition coils from the misfiring cylinders to cylinders that are not misfiring
- If the misfires follow to the new cylinders then you have your issue
- Otherwise, swap the spark plugs from the misfiring cylinders to other good cylinders
- If none of these then fuel injectors are a possibility, but they can be complex to swap
Again, the above steps work well if you have cylinder specific misfire codes alongside P0300. It’s easy to swap ignition coils and on most engines should only take about 10-30 minutes to swap a few coils around. Spark plugs are also easy, but they lie below the ignition coils so it’s best to start from the top.
Diagnosing With Other Codes
Running through all of the scenarios is tough. We will provide some of the basics, but some of these parts can be more complex. Less experienced DIY’ers may consider seeking a professional repair shop. Anyways, if other codes are present with P0300 then check the following:
- Essentially same first steps from above. Confirm which codes are present. Delete the codes and proceed on a few test drives. If the codes come back then it’s time to diagnose the problem(s) at hand
- Double check the basics like ignition coil wires, vacuum hoses, etc. Ensure there are not any loose connections, broken wires, or cracked/dirty sensors that may cause code P0300
- Check fuel pressure if any codes are present indicating low fuel pressure. The fuel pump and fuel pump sensor are two common issues
- Consider camshaft and crankshaft sensor issues. These will often throw a code suggesting something is wrong with the respective sensor
- Perform compression and leakdown tests. This will confirm whether any cylinders are losing compression that may cause misfires
Again, there are lot’s of different possibilities if the spark plugs or ignition coils are not at fault. Fortunately, those are two of the most common causes of P0300 misfire code. Otherwise, there are tons of potential problems that cause random/multiple cylinder misfire codes.
The most important thing is using the internet and some critical thinking. Find other codes present with P0300. Determine the meaning of the other code and use that info to diagnose the problems. That usually provides the best starting point to diagnose and fix P0300.
P0300 Code Fix/Repairs
Obviously, the specific repair for each P0300 code can be very different. We’ll move onto repair costs in a moment. The main reason we’re discussing the fix is to address some basic concepts. If you’re struggling to diagnose the issue at hand then you may consider a repair shop. It can end up being more expensive if you start blindly replacing parts that aren’t the actual problem.
Spark plugs and ignition coils are the basics. Most should be able to swap these around to track down the issue. We always recommend replacing all spark plugs at the same time if that’s the root cause. Same goes for ignition coils. If more than one goes bad then chances are the rest are also on their last leg.
Other P0300 causes like cam or crank sensors, fuel delivery issues, and bad fuel injectors can be complex to diagnose and replace.
Code P0300 Repair Cost
Now that you know the issue at hand what is the repair bill going to look like? Below are some common costs for repairing the underlying issue that’s triggering fault code P0300:
- Spark plugs: $25-500 (assuming all are replaced)
- Ignition coils: $100-600 (assuming all are replaced)
- Fuel injectors: $400-1,500+
- Fuel pump: $100-1,000+
- Sensors: $40-300+ (fuel pump sensor, crank sensor, cam sensor)
- Vacuum hoses: $0-200
Don’t panic too much about the higher end of a few of these numbers. A set of 4 spark plugs on a 4-cylinder can come in as cheap as $25 and about $100 for ignition coils. With more cylinders parts generally get a bit more expensive. If you’re paying a repair shop then it can add in another $100-300 in labor.
Unfortunately, fuel injector issues are most common on direct injection engines. These high-flow, precise injectors can easily run $500 for a set (we spent about $1,700 on new direct injectors for an inline-6 BMW engine). Direct injection engines also run into high-pressure fuel pump problems which can be a big bill.
Otherwise, it usually comes down to the basics like vacuum hoses, sensors, and electrical connections. All cheap parts for the handy crowd so repairs can be cheap. End up at a repair shop and P0300 repair bills can add up, though.
DTC P0300 FAQ’s
Next up are a few frequently asked questions regarding DTC P0300. A lot of this may be duplicate with the info covered above in the article.
What Does Fault Code P0300 Mean?
P0300 means Random/Multiple cylinder misfire detected. Essentially, at least two of the engines cylinders are misfiring (not reaching a complete air-fuel burn).
How Expensive is it to Fix DTC P0300?
Costs can vary quite a bit. Simple problems may be $0 or close to that cost if it’s a simple hose or other issue you can fix on your own. More expensive P0300 engine problems like fuel pumps and injectors can run $1,500.
Can I Drive With Fault Code P0300 Present?
More often than not it is safe for you, your passengers, and the engine to continue driving with code P0300. That does NOT mean you shouldn’t diagnose and repair the issues as soon as possible. However, it doesn’t usually pose a major risk to the engine or you.
Use your own judgement, though. If the car feels unsafe then pull over in a safe location and have the vehicle towed. Also, if there are more serious problems like loss of oil pressure, overheating, etc then it’s best to pull over as soon as it’s safe.
What is the Most Common Cause of P0300?
Spark plugs and/or ignition coils are the most common causes. These are typically the best starting point for diagnosing engine fault code P0300. Don’t overlook other basics like hoses and wires.
Why Do I Have Code P0300 and P0301?
Well, P0300 represents multiple misfires. P0301 means cylinder 1 is misfiring, P0302 is cylinder 2, and so on. It’s common to receive these fault codes together. Consider it a win since knowing the cylinders at fault makes it that much easier to diagnose and repair.