Check Engine Light Misfire Detected - Code P0300 - Ignition Coil Diagnosis

Is your check engine light on and your engine's running rough? It may be a bad ignition coil. I'm gonna show you how to diagnose it.

So, at this point, the first thing we wanna do is scan the vehicle with a scan tool and see what kind of codes we have. So, you probably have a P0300 which just basically says there's a misfire detected, it doesn't tell specifics, and then you may have other misfires detected. A 303 or a 306 is probably where our fault is. Could be 303 also. And then some primary, secondary circuit codes, random misfires. And those are all history codes. So, that's a good starting point. We wanna check out cylinder number six and then maybe cylinder number three.

So, this engine's running rough. It's hard to visually see it, but with a scan tool, I can actually see the misfire count going up. So, we know there's a problem with cylinder number six, one through four. Once in a while, I get a misfire from number three. I'm not that concerned with that one. That one is probably spillover from another one and then go up to cylinder six is the constant one. So, we wanna check out cylinder number six.

Now, we need to determine where cylinder number six is. Generally on the engine, wherever the front of the engine is, the head that's closest to the front of the engine is gonna be the bank one head, which is gonna be your odd cylinders, one, three, five, seven and the other bank would be two, four, six, eight. Not always the case, it's always good to look them up. But in this vehicle, this happens to be cylinder number one. So, bank two is on this side. So, the third one back would be cylinder number six. So, this is cylinder two, this is four, six, and eight. Now, disconnect the connector for number six. Just take a look at the connector and make sure it's not melted. I don't see anything melted, you could drag test the terminals to double-check them. Now, I'm gonna pull this coil out using a 10-millimeter socket. Pull that bolt out and look at the coil. I don't see anything melted on the coil there either. So, what I'm gonna do is I'm actually gonna swap the coil with another one and we'll see if the misfire moves. So, this is cylinder number four. Disconnect the connector here. Stick that one in number six. Since we didn't have a misfire on cylinder four. Connect the connector, put the bolt back in, put the bad coil that we assume is bad in number four. I'm gonna tighten these up. And we'll start the engine and check the scan tool and see if it moved.

All right. So, now we check cylinder number four and we see cylinder number four is actually misfiring. So, our misfire did move. If I go to look at cylinder number six, it's not misfiring. So, we know the problem is with the coil.

Now, we know that ignition coil is bad. It's always a good idea to replace all the ignition coils at once. And while you're doing that, replace your spark plugs.