P0302 Code: Cylinder 2 Misfire Detected

The P0302 engine code can cause serious drivability issues, so you’ll need to address the underlying problem (or problems) right away.

If the check engine light has popped up on your vehicle and the OBD-II scanner reads a P0302 code, here’s everything you’ll need to know to help you address it.

What Does the P0302 Code Mean?

Diagnostic trouble code (DTC) P0302 stands for “Cylinder 2 Misfire Detected.” The code indicates that your car’s primary computer, also known as the powertrain control module (PCM), has detected a misfire on cylinder 2.

Cylinder number 2 refers not to the second cylinder in the firing order but the cylinder numbered “2” in the arrangement of cylinders on the engine. For example, on a Ford V8, the cylinders are numbered 1 to 4 on the passenger side bank and 5 to 8 on the driver side bank. On a Chevy or Dodge V8, the cylinders are numbered 1-3-5-7 on the driver side bank and 2-4-6-8 on the passenger side bank. Four cylinder inline engines are numbered 1-2-3-4 beginning on the timing belt end of the engine. This information is important but has little to do with a P0300, which doesn’t specify a particular cylinder.

But wait: How does the engine computer know which cylinder is misfiring anyway? Well, it works like this:

To begin with, the PCM (Engine Computer) has to establish a baseline of how the Crankshaft Position Sensor pulses are spaced. This baseline snapshot is something the PCM learns and stores on its own, usually during deceleration, when the injectors are turned off and the engine is being driven by vehicle momentum through the transmission (coasting), because none of the cylinders are contributing power at that point. Without this information stored, the PCM cannot detect misfires. Technicians will use scan tool software to make the PCM learn this faster after they replace certain components or erase the PCM’s memory.

This baseline “snapshot” has different names among manufacturers. Chrysler refers to this piece of stored information as the “Adaptive Numerator.” GM and Ford refer to it as “Crank Relearn” or “Case Relearn.” One way or another, the PCM compares the live crankshaft pulses with the pattern it stored during the Crankshaft Learning process. The PCM typically updates this information periodically on its own as a part of the “adaptive learning” process PCMs use.

The point of the “Crankshaft Learn” snapshot is that the PCM needs to know when the engine is misfiring, i.e., which cylinder isn’t contributing, and it can tell by watching the crankshaft slow down every time a particular cylinder doesn’t fire. It determines that by comparing the stored pattern with the live one. But there’s another factor the PCM uses.

The point of the “Crankshaft Learn” snapshot is that the PCM needs to know when the engine is misfiring, i.e., which cylinder isn’t contributing, and it can tell by watching the crankshaft slow down every time a particular cylinder doesn’t fire. It determines that by comparing the stored pattern with the live one.

–Richard McCuistian, ASE Certified Master Automobile Technician

Each piston travels up and down four times in a cycle, but each one only generates power on one of its four strokes. The crankshaft is able to maintain an even speed because every cylinder is contributing evenly its share when the engine is loaded. Again, if a cylinder isn’t producing power, the crankshaft will very briefly slow down when it’s that cylinder’s turn to fire.

So the crankshaft makes two full turns to complete a cycle and the camshaft only makes one full turn during a cycle because it spins at half crankshaft speed. For that reason, the PCM uses the Camshaft Position Sensor to identify which cylinder should be firing when the crankshaft slows down.

The PCM measures how often a misfire happens within two different rpm windows to determine the frequency/severity of a misfire. It stores misfires within a 200 rpm window of time and also within a 1000 rpm window of time. Obviously, a misfire that happens multiple times with a 200 rpm window is the most serious.

A misfire is caused either by incomplete combustion (or the absence of combustion) in one cylinder. Combustion is a small explosion that takes place when a pressurized air-fuel mixture is ignited inside the combustion chamber above each piston. These explosions are timed very precisely for optimum power and efficiency. The combustion event superheats the inert nitrogen (which is 78 percent of the air charge) and the superheated nitrogen expands to drive the piston downward, which applies torque by way of the crankshaft to create the rotational force delivered to the transmission or transaxle, which then applies torque to the drive wheels.

Code P0302 is part of a series of misfire DTCs that range from P0300 to P0012. Each code between P0301 and P0312 indicates a misfire on a particular cylinder. For example, code P0301 indicates a misfire on cylinder one and code P0312 indicates a misfire on cylinder 12 (if your car has a 12-cylinder engine). Code P0300 is a bit different because it implies a “random misfire” rather than a misfire on a particular cylinder.

Again, when there is a misfire, the crankshaft speed becomes slower than usual during the brief interval when the cylinder in question is supposed to be firing. The PCM continually monitors the crankshaft speed and notices any rpm loss that happens when a misfire occurs, even if it only happens once in a while, but misfires that happen a sufficient number of times within the 200 or 1000 rpm window (the ECM/PCM keeps a running total) will store trouble codes. The device will set a P0302 code when it detects a frequent misfire on cylinder number 2.

What are the Possible Causes of the P0302 Code?

There are many factors that can cause a cylinder 2 misfire—the most common of which are the following:

• Fuel delivery issues (e.g., a faulty fuel injector or damaged injector circuit)
• Ignition system problems (e.g., a failed coil pack or worn spark plug)
• Engine mechanical issues (e.g., a sticking valve or weak piston rings)

It’s worth noting that, if other misfire codes accompany a P0302, there will likely be more than one potential cause. Code P0302 by itself is a good indicator that the problem is with cylinder 2 only.
On the other hand, multiple misfire codes can indicate an issue, such as a vacuum leak or low fuel pressure, that affects various cylinders. Also, a consistent misfire on one cylinder will usually cause the ECM/PCM to shut the injector down on that cylinder until the next start. It does this to protect the catalytic converter.

To make diagnosis even more difficult, a cylinder 2 misfire can confuse the PCM and cause P0300 and other misfire codes to set.

What are the Common Symptoms of the P0302 Code?

As previously mentioned, a P0302 may be accompanied by other codes, in which case you may observe symptoms that may not be mentioned here. If your PCM is only storing a P0302, however, these are some common signs that your vehicle may exhibit:

• Check engine indicator light is on or flashing
• Running rough
• Stalling
• Difficulty starting the engine
• Foul odor coming from the exhaust
• Decrease in power
• Excessive fuel consumption

How to Diagnose the P0302 Code

P0302 should be fixed as soon as possible. You’ll have to look at all possible causes to diagnose the problem properly. Have a professional mechanic check your vehicle if you don’t have the required DIY auto repair experience and skills. The videos below could give you a better idea of the diagnostic procedure if you’re still interested in checking your own vehicle.

How to Fix the P0302 Code

To be honest, there are no simple, umbrella solutions to most—if not all—OBD-II trouble codes. If you aren’t well-versed with automotive repair, it may be best to leave it to a professional.

However, if you are confident in your DIY skills, the first step is to properly diagnose the underlying issue. Once you’ve determined what’s causing the P0302 code to set, you can then figure out the appropriate fix with the help of online auto repair resources and guides.

You could also get an ALLDATA single-vehicle subscription, which will definitely be useful for any future repairs your vehicle may need.

Lastly, different carmakers and vehicles may have their own specific repair instructions. What works with one car might not work for another, so make sure to consult your owner’s manual before attempting to fix a code P0302.

Get the Right Spark Plugs, Fuel Injectors, or Piston Rings for Your Vehicle

Damaged spark plugs, fuel injectors, or piston rings can trigger the P0302 code and cause various engine-related symptoms. Fortunately, you can prevent this problem from escalating by purchasing a replacement spark plug, fuel injector, or piston ring from CarParts.com.

Finding the appropriate engine components for your car is simple and straightforward here at CarParts.com, and you can do it from the comfort of your own home. Simply input your car’s year, make, and model into our vehicle selection to view a list of suitable parts. Our spark plugs, fuel injectors, and piston rings are supplied by some of the most dependable manufacturers in the business, ensuring quality and durability. We also have strategically located warehouses across the country, so you can receive the parts that you need in a matter of days.

Our affordable parts let you get the most bang for your buck. Get spark plugs, fuel injectors, or piston rings here at CarParts.com today!

Products Mentioned in this Guide