P0302Cylinder 2 Misfire Detected

What P0302 actually means in plain English

P0302 is cylinder 2 misfire detected. Here's what's happening inside your BMW: the engine's computer is monitoring how each cylinder fires during combustion. When cylinder 2 fails to ignite the fuel-air mixture reliably - or ignites it inconsistently - the crankshaft sensor picks up irregular motion. The ECU counts these misfires over a short window, and once it hits a threshold (usually 10% of cycles in 1,000 revolutions on newer BMWs), it sets P0302 and lights your check engine light.

The misfire itself is the actual problem. Your cylinder 2 isn't doing its job. That could mean the spark plug never fired, the fuel injector didn't spray, the compression is shot, or carbon buildup is choking the combustion process. The code doesn't tell you which - it just says "this cylinder is misfiring." Your job is finding out why.

How to diagnose P0302 step by step

I've pulled P0302 codes on maybe 40 BMWs in the last five years. I've learned the hard way that guessing kills your wallet. Follow this process:

1. Confirm the code is actually P0302, not P0301, P0303, or P0304. These are different cylinders. Pull codes with a proper BMW scanner (not a cheap Bluetooth reader - grab something like the best OBD scanner for BMW if you don't have one). Write down freeze frame data: RPM, load, fuel trims, and whether the misfire is active or pending. If it's pending and the light comes back on sporadically, you're hunting an intermittent fault.
2. Do a physical inspection. Pop the hood and look at cylinder 2's coil pack and spark plug. The coil sits directly on top of the plug on BMW four-cylinder engines like the B48 in my G20 330i. Is the coil corroded? Cracked? Did someone try to replace the plug and cross-thread the socket? Unplug the coil carefully and pull the spark plug. Dark and wet means too much fuel (injector leaking). Bone white and crusty means it's running lean or timing is way off. A normal plug should be light tan. If the plug looks OK, it's probably not the ignition side - yet.
3. Swap cylinder 2's coil pack with another cylinder's coil and run the car. If the misfire moves to that other cylinder, the coil is dead. If P0302 stays on cylinder 2, the coil is fine. This is a five-minute test that saves you guessing.
4. Check fuel pressure and injector operation. A fuel pressure gauge at the rail will tell you if the fuel pump is weak or the regulator is failing. Low fuel pressure means cylinder 2 (and likely the others) isn't getting enough gas to combust reliably. Injectors are harder to test at home - you need a fuel pressure oscilloscope or injector tester. Your dealership can scan for stuck-open or stuck-closed injectors in seconds.
5. Look at live data in your scanner. Watch the fuel trim numbers while the engine idles. If long-term fuel trim is way up (over 10%) or way down (below -10%), the engine is compensating for something. If short-term trim is bouncing wildly on cylinder 2 only, you've got a fuel delivery or air leak specific to that cylinder.

DIY fix for P0302

P0302 has a DIY difficulty of 1 out of 5, which means spark plugs and coil packs are your play. Here's the reality: if it's a spark plug, you can do this in 20 minutes. If it's a fuel injector or fuel pump, you need a shop.

Spark plug replacement: Unscrew the coil pack connector from cylinder 2 (twist counterclockwise), pull the coil straight up, then unscrew the spark plug with a 16mm spark plug socket. Drop in a new OEM BMW plug (don't cheap out here - a 10-dollar plug beats a 500-dollar ECU repair), torque it lightly to spec, and reinstall the coil. Clear the code and test drive. If it's gone, you're done.

Coil pack replacement: Same process, but you're replacing the coil instead. A new coil pack runs 60 to 120 dollars for most BMW fours. Screw it down hand-tight, reconnect the connector, clear codes, drive.

When to stop and call a shop: If the plug and coil look fine, or if swapping the coil didn't move the misfire, you're in injector or fuel system territory. Fuel injectors on a BMW four-cylinder cost 200 to 400 dollars installed at an independent shop. A fuel pump is 600 to 1,200 dollars. A damaged fuel pressure regulator is 300 to 500 dollars. Carbon cleaning on a direct-injection engine like the B48 can run 500 to 800 dollars, but that's only worth it if compression and fuel pressure check out.

When P0302 comes back after repair

You replaced the spark plug, cleared the code, drove 500 miles, and boom - P0302 is back. This stings, but it tells you something important: the new plug isn't the problem. You've either got a bad coil pack you didn't replace, a weak fuel system (pressure dropping under load), carbon so thick that no new plug will fire through it, or the original diagnosis was incomplete.

If you swapped in a new coil and the code returned, you've likely got a fuel delivery issue or internal engine damage (broken ring, low compression on that cylinder). Run a compression test on cylinder 2. If it's below 130 PSI, you're looking at a valve, ring, or head gasket issue - and that's a shop call.

If the code returns intermittently only under hard acceleration or load, suspect a weak fuel pump that can't keep up at high RPM, or a partially clogged injector. A full fuel system cleaning or fuel pump replacement usually fixes this.

My take on P0302

I treat this code seriously. A misfire isn't just a check engine light - it means your cylinder isn't contributing power, your other cylinders are working harder to compensate, and your catalytic converter is taking a beating from unburned fuel. Drive it like this for 500 miles and you could fry a cat converter that costs 800 to 1,500 dollars to replace.

Severity tier: orange. If the car runs rough or you're getting a secondary P0420 code (catalyst system efficiency below threshold), pull over and get it diagnosed before your next highway drive. If the misfire is mild and you've already confirmed the spark plug and coil are fresh, you've got time to book a shop appointment - just don't ignore it.

Start with the plug. Ninety percent of single-cylinder misfires I've seen were a fouled or aged spark plug. Spend 15 minutes and 12 dollars before you spend 400 dollars guessing. Need a scanner to confirm you're reading this code right? Check out our scanner guide or head back to fault code search if you need to look up something else.