March 17

2007 Mazda CX9 – PCM and Ignition Coil



Mark: So today's victim is a 2007 Mazda CX9. This is a little bit of a rarer vehicle. What was going on with this car? 

Bernie: Yeah, so we'd done a podcast on this exact same issue, so if you wanna know more, there's another podcast somewhere. But basically the engine had developed a misfire. He'd had all the ignition coils replaced and sparked plugs, and still a misfire persisted. And I'm not sure if it was another shop or whether he did it himself. I assume it was at another shop. The PCM was bad, powertrain control module. Basically the computer that runs the engine and transmission, it was bad.

It's a common fault with these vehicles. If you have an engine misfire, we'll talk a little more in a minute. So he basically had the computer out, sent it off somewhere to have it repaired to one or two places. They couldn't repair it. And I guess he'd seen our video. Called me to talk to me about, Hey, what can we do about this vehicle? So that's how the vehicle came to our shop and yeah, that's kind of the story. 

Mark: What did you end up doing, well, I guess first of all, what'd you do to confirm the diagnosis? And then what did you do about the PCM? 

Bernie: Well, I didn't really do anything to confirm the diagnosis cuz the vehicle wasn't running, the PCM was out. So sometimes we just have to take whatever previous information at face value and just say, okay. He needs a PCM to get the thing going. Let's do that. So based on experience, the first place I called was the Mazda dealer and said, you know, how much is this thing? Can you get it? The customer said, yeah, go ahead and do it. 

So it's basically a brand new, direct from the Mazda dealer part. You know, we went through a big rigmarole on the last one we worked on like this. Sending the PCM off, they apparently repaired it. It had a misfire and a different cylinder, sent it back. It had misfire another cylinder and finally said, Hey, we can't fix this thing. Which was kind of obvious. 

So through the rebuild, we actually managed to get a PCM, but it was a lot of work and it took a while to get it. So the dealer got one within, I think three days to us. It's over $2,000 Canadian, so not cheap, but you know, it's still not an insane amount of money and a lot cheaper than a new vehicle. So we ordered that part in, and that's kind of where it went. So we figured at that point, gotta put the PCM in and then see what happens from there.

Mark: So once you installed it, did you have to reprogram the PCM? 

Bernie: Yeah. It needs to be programmed for the vehicle. So we did that and had it programmed and turned the key and it fired up right away. 

Mark: So what else was there going on with the vehicle?

Bernie: Yeah, so that's the thing, it fired up right away, but it was misfiring, running rough. Pretty good, but not perfect. You can tell there was a cylinder misfiring, and a trouble code occurred pretty quickly in the computer for a cylinder one. I don't have the number of the code, but cylinder one, ignition coil circuit problem.

So that wasn't too promising to see because he'd had all the coils replaced. You could see by looking, you know, at the coils, the ones we can see, they were all brand new. Good brand of ignition coil and figure, okay, well that's kind of odd, but you know, here we are. So at this point we had to do some further diagnosis to figure out what was going on. Why that circuit kept happening. 

Mark: And what did you find? 

Bernie: So as I said, it was number one cylinder ignition coil. So I thought, well, great. It's a V6 engine and the front three ignition coils are really easy to access, but cylinder number one is at the back of the engine where the intake manifold plenum hangs right over the back of the engine.

You have to pull that off. So it's a lot of extra work. The front three coils and plugs can be done in a few minutes. The rear ones take an hour or two, to do. There's a lot of extra work. But fortunately number one cylinder, you can actually access the bolt and remove the coil without pulling the intake plenum.

So I thought, great, fantastic. Well undid the bolt and I couldn't pull the coil out. Like it would not, they sit in a tunnel and I just could not pull the coil out, it just wouldn't come out. So I had to pull the plenum off and extract the coil, break it apart, and this is where the interesting stuff was found.

So let's get into the picture show, cuz this is where the picture's worth a thousand words. So this is a picture of the PCM. Actually, I'll get back to this one in a second. 

2007 Mazda CX9 - PCM and Ignition Coil

So this is what the coil looked like after I pulled it apart and broke it in half. This is the top of the coil. This is the bottom of the coil. But you can see this is all, it looks really ugly. Like there's a bunch of weird stuff that's festered out and I'll show you a picture of a good one, cuz that makes more sense to what we're looking at. 

2007 Mazda CX9 - PCM and Ignition Coil

So this is a brand new good one. Disregard where my mouse pointer is moving, this GM part number. I should have got a blank background, but I didn't. Anyways, this is what a good brand new coil looks like. And this is the coil came out. So this explains why I couldn't get out this tube cuz this coil had basically exploded, electrically exploded inside the tunnel and it was stuck.

2007 Mazda CX9 - PCM and Ignition Coil

And so, I was able to pry it out, but that explains why it wouldn't slide out. Whereas this one just fits right in. And what I will say, and I wish I could share the smell of this thing, like just the stench of this burnt electrical component. It was just horrifically toxic. Actually you probably would never wanna smell it. It's just awful.

Again, there's kind of the view, there's the top of the coil broken off, and the coil itself.  

2007 Mazda CX9 - PCM and Ignition Coil

Mark: So was there any way to determine that this was the supposed new coil that was put in, or is this the old coil and they couldn't get it out so they just. 

2007 Mazda CX9 - PCM and Ignition Coil

Bernie: No, no, this, this was a brand new coil. This brand of coil is a blue streak. It's an aftermarket brand, but all of the coils were the same. So it was definitely brand new. So what I theorize happened because, you know, why would this coil go bad? My theory is that the old computer, there's a driver, it's probably a power transistor that causes the coil to spark at whatever time you know, it's supposed to deliver it spark.

2007 Mazda CX9 - PCM and Ignition Coil

My theory is that power transistor was probably stuck on, it was delivering full power to this coil all the time and it just burnt up. So that's all I can conclude. That's the only thing I can see. But I have to say, in all the years I worked on cars and I've changed a lot of ignition coils, I mean, there's a lot of that have gone through our shop, have never seen anything like this before. It was quite unusual. 

2007 Mazda CX9 - PCM and Ignition Coil

So this is a picture of the old PCM, the powertrain control module. There's two connectors that plug in. It looks like they could put a third one in, but they don't on this particular one. But the very critical thing, of course, is having this part number here. This has to be an exact match for the vehicle because, you know, depends on whether it's an all-wheel drive or two-wheel drive, automatic or standard.

There's all sorts of things that go into making this thing do what it does. So the part number has to be an exact match. You can't say EF or FG or anything. It's gotta be an exact match. You'll notice, even though it's a Mazda, it says FoMoCo. It's a Ford, basically, you know, Ford and Mazda, I don't say they're in bed together, but you know, they work together. So this is a Ford part. It's funny, you know, I think all the cars we work on, Land Rovers, Jaguars, Volvos, a lot of times they're FOMO codes, so they've got their fingers in a lot of different manufacturers, in various areas.

Mark: So once you replaced the coil, how did the car run? 

Bernie: Like, brand new. It was beautiful. Yeah. Really nice. Beautiful six cylinder engine and yeah, ran really well. 

Mark: So, as this is the second time we've talked about this with CX9s, how are these vehicles for reliability? 

Bernie: Well, I'd say that this is certainly one of the larger faults of these vehicles, and so if you own one and you keep it for a while, now this is an 07, you know, plus or minus a few years. I'm not sure the sort of life range when this problem sort of started or stopped, but they're generally a pretty reliable vehicle. This is probably, I'd say, consistently the worst fault of the vehicle. And by the time you add the coils and do the whole job, it's probably like in Canadian dollars, four to $5,000.

You know, it could cost you in terms of having all the coils, maybe, yeah, three, three to five. That's kind of a big range. But, you know, that's a pretty expensive repair to do on a vehicle. It doesn't really involve a major component like an engine, but once it's done and done properly, you shouldn't have any problem with it. This vehicle should go for another 10 or more years without any issue. So that's probably not really a huge thing, but it's something you don't see on most vehicles. So other than that, they're pretty reliable, they're a pretty good vehicle. 

Mark: If you need service for your Mazda in Vancouver, the guys to see are Pawlik Automotive. You can book online at Or you can call them (604) 327-7112. You have to call or book online ahead of time. They're always busy. Pawlik Automotive, Vancouver, BC Canada. Thanks so much for watching and listening. We appreciate it. Thank you, Bernie. 

Bernie: Thank you, Mark.

About the author 

Bernie Pawlik

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