December 22

2009 Mazda CX7, Engine Computer



Mark: Hi, it's Mark Bossert. I'm here with Bernie Pawlik. Pawlik Automotive in Vancouver, BC, Canada. Vancouver's best auto repair service. 25 times voted best auto repair in Vancouver is voted by their customers. And we're talking cars. How are you doing Bernie? 

Bernie: Doing well. 

Mark: So today's victim, and this is quite the story, the 2009 Mazda CX7. What was going on with this vehicle? 

Bernie: So this vehicle came to us, towed in from a dealership that did not want to fix this car. A Mazda dealer did not want to fix their own vehicle. It had died on the customer and they determined the computer was bad. It had actually burnt up. The computer actually burnt up inside. We'll get to pictures really fast. It's interesting. 

They got another used computer, put it in, that burnt up. And I believe they tried two computers and then decided that they didn't want to do anything more.

Good news for the customer. I asked the owner, what did they charge you? He goes, they actually didn't do anything. They didn't charge me anything. They let it go. So I thought that was pretty honourable of them. I guess they just decided to give up early on the project.

But anyways, I'm just going to show a picture of what we were up against. Cause it was pretty interesting. There's the car. Fixed and done. So that's the end story. Let's get looking at pictures of the computer. 

2009 Mazda CX7, Engine Computer

So there's the circuit board of the computer with the cover removed. You can see a very black, burnt area here and even to the point where there's actually one of the pins on this computer is actually burnt the connection off the board. 

2009 Mazda CX7, Engine Computer

And a closer view of that right there and it reveals a lot of parts missing. Got very hot. This is again, this pin here completely gone, burnt off. So that was what we were up against. 

2009 Mazda CX7, Engine Computer

Mark: So this is not normal for your testing and diagnostic process. So where do you start? 

Bernie: Yeah, we have several technicians in our shop. Our service advisor used to be a tech. None of us had ever seen anything like this. And I mean, obviously, there was something that caused it to burn up. And the fact that, you know, Mazda tried a couple computers, I thought, okay, we need to be a bit cautious here and figure out what caused it. So what's very common on Mazda's, you know, these models, similar models is ignition coil problems.

They'll cause computer failures. And so we did a little investigating and we found an issue with at least one of the ignition coils. I'll go back and do another screen share. And there's our computer again. This is one of the ignition coils. You can see this sort of bulge burnt spot on this particular coil here. Figured, okay, that's gotta be a good reason for the computer to have burnt up now, you know, the shorted out coil, we replaced all the coils, the spark plugs did a few other basic tests and then ordered up a computer.

2009 Mazda CX7, Engine Computer

We weren't able to get a new computer at the time. We can only find a used one. It was very difficult to find it. There's not many of these around. So we acquired it through the US, we're in Canada, so it makes it a bit more of a pain to get a computer, but we were able to get a refurbished computer. Ordered that in, put it in, and it actually fried that computer, too. 

Mark: So when you say it fried the computer, like, how is this happening? How quickly is it? 

Bernie: Yeah, within like 30 seconds of running. And it's a bit of a procedure because the security system is programmed to the vehicle. It won't start. So once we had the security system programmed, we got it done, we started it up and it ran for about 30 seconds and then there was some smoke came out and burnt up and we go, okay, obviously it wasn't the coils. It's a much more serious issue. So ordered up another computer at our own expense at this point, because I don't want to charge people for stuff that we haven't done.

We managed to get another computer, ordered that up. And again, it takes like a week or two for us to get it. So in the meantime, I was like, okay, we've got to go through this thing and test every circuit on this, you know, that's being driven by the computer because something, there's some kind of short that's overloading the system.

So that's what we proceeded to do. We tested everything in the vehicle and the only issue we found was a circuit was out of range was there's an electric EGR valve. And it had been replaced with an aftermarket part. And one of the circuits, there's four circuits, one of them had excessively low resistance, which can cause way too much current flow.

And that actually happened to correspond with the pin that was burnt off. So I thought, okay, I think we're onto it here. But anyways, we did that, tested a few other things. And just really were, was very cautious before we put another computer and I go, I don't want to fry another computer up.

We got to figure this out. So we replaced that. The alternator, I said, figure, let's get that tested in case it's putting out too much voltage and blowing the computer up, had that tested and just for good measure, had another voltage regulator put in because it's also computer controlled. So it could have caused an issue. Had that done, got another computer and it didn't burn up. So I think we figured we'd found it. 

Mark: So that seems like, and this is over a period of a fair amount of time as well.

Bernie: A couple of months, this procedure went on just because again, there isn't a computer down the street, you know, or there isn't a pile of used computers kicking around that we could try. So, yeah, it was a time consuming process. 

Mark: So that's a big process. What happened? 

Bernie: So, we got it running. It didn't burn up, but there was a couple of trouble codes that kept reoccurring and then it would run fine. And a couple of trouble codes and being that it was a refurbished used computer and we tested all the circuits, we figured you know what, this has got to be a defective computer.

So sent it back to the company, to be honest, I'm not going to name the company, but I'm not very happy with the way they just didn't give me a lot of confidence in who they were and the product they were selling. So anyways, we did get another computer sent to us. We tried that, it worked great, and then it'd start running weird again.

And so we go, okay again, concluding we tested all the circuits, and everything was fine, there's gotta be a defective computer. I started making some other inquiries, and lo and behold, actually, Mazda was now selling these computers, they were actually available brand new. Talked to the owner, said, hey, it's gonna be a lot more money, said, do it.

So, the owner was on board to get the car fixed, he liked it, liked the vehicle. So we got a new computer, and put that in. 

And then what happened? 

It ran fine and then it ran badly again. We go, okay, what the heck is going on here? We know, the good thing is, having a brand new computer, we knew, okay, the computer has got to be okay.

There's got to be some kind of other wiring issue or some other faulty components. And there was actually a couple other faulty components I haven't even left out. There's an oxygen sensor that was setting a code that you know, the we'd replaced as well. To make a long story short, we finally realized it was actually a problem in the main engine wiring harness that connected to the computer. And in hindsight, it all kind of made sense because, you know, having had that fire and all that heat, obviously caused some sort of damage. 

We're going to look at a few more pictures here. 

There's the wiring connector that we found to be faulty. Although we actually took it apart and never found a fault in it. And you know, each of these little holes here, there's a wiring connector on there. And I used an ohmmeter on every single one of these and tested every circuit and every one of them tested fine. Except that EGR one, of course, which we'd fixed. And after that, it tested properly.

2009 Mazda CX7, Engine Computer

So by testing that way, it seemed like everything was fine. But obviously there was an issue somewhere in there and I actually cut the wiring harness apart and broke it apart and never found a problem. But there was obviously some kind of bad connection with one of the pins in there.

So this is the wiring harness we replaced. This is the brand new one, fortunately still available from Mazda. Again, not a cheap part, but that's basically it. So there's two connectors here. One, I'm moving my mouse point around. That's the white one that we looked at there. There's another one here. These all come in this harness. This connects right to the battery. It's called the emission wiring harness. Some of these connect up to the engine where there's an actual engine wiring harness. But we were actually able to wiggle the wires. And I don't know why we didn't do this earlier, but, you know, we just follow our procedure. Wiggling the wires here. It actually caused the vehicle to run worse and better. And so we, okay, that's gotta be the issue. 

2009 Mazda CX7, Engine Computer

Mark: So something as simple as bad connections can totally ruin how your vehicle runs because everything's running on computers now. 

Bernie: Oh yeah, totally. And the connections have got to be perfect. So again, it wasn't like we didn't test the wiring you know, we did test everything from one end of the circuit to the other, but the one thing that is interesting about testing wiring is that, it's one thing to test it with an ohmmeter, but there's another thing to test it while the vehicle is actually running and there's loads on the wires and that does make a big difference.

So it's always best to test circuits live. But of course, when the computers were burnt up and fried, we're in a sort of, I'm trying to think of another analogy. If someone's drowning, the first thing you got to do is get them out of the water and get them breathing again. And so we had to get this car breathing again, so to speak, before we could move on to the next step. 

Mark: So a long repair process, I'm sure it was fairly expensive. 

Bernie: Yeah, it was. And you know, not entirely profitable for us at the end of the day, but you know, vehicle's fixed. Customer's happy. We're happy. I mean, I like seeing a job that's done in a vehicle that works at the end of the day.

Mark: So Mazda just kind of passed on this because they sort of foresaw that this might be very hard to find and you guys don't mind doing these sorts of jobs? 

Bernie: No, exactly. I think that's it. Dealerships do a great job of service when a vehicle is well, when it's under warranty, they have to fix it because they're legally obliged to. But afterwards, I think they're much more like, Hey, we'll fix stuff that we can fix. And otherwise it's like, wow, this is too expensive to fix. Why don't you just walk into our showroom. Here's the newest and latest model. And we'll take this one off your hands. So they kind of run two businesses sometimes. The service and if it gets too complicated, I think they're not interested and maybe they're smart.

Mark: So I know you research these things quite a bit and look at the repair history across North America. How common of an issue is this? It must be becoming more common if Mazda has gone back to making the board. Is that a fair assumption? 

Bernie: Yeah, but we did not run into anything. And besides having databases that we can look at for, you know, burnt computers and things, we have technical services and people we can call and ask for advice and most of it was like ignition coils are kind of it. So, I really think, you know, at the heart of the problem, I believe it was the EGR valve, the electric EGR valve, just with that high resistance, but even then.

If that circuit would have drawn, I did a little calculating would have drawn one amp, I believe. And with the extra resistance, it would have drawn two, which is twice as much, which isn't a lot, but maybe that circuit, just whatever components in that circuit, just two amps is too much. 

Mark: That's a lot of current.

Bernie: Yeah, I guess it is. These are all things that you know, yeah, I mean, that circuit board is not meant to handle a lot of current. Although there are some circuits that will draw two amps, but that was obviously too much for that particular thing. So again, we don't know, because I wouldn't want to put the old valve in and blow another circuit board and then wreck another wiring harness just for experiment sake, you know?

Mark: So how are Mazda CX7s for reliability? 

Bernie: Well, they're generally pretty good cars. And I think, you know, with these, I think we've done another podcast on CX9 with a computer problem.

So I think some of these Mazdas, computers are definitely a problem. They're weak when it comes to like ignition coil or component failures. So I'd say that's probably one of the only issues. Other than that, I think they're pretty good cars. This is a really nice car. It had like 108,000 kilometres.

I mean, after, you know, it was fixed and running. It's like a brand new car. So, you know, a lot of money to fix, but is it worth it? I think so, because otherwise you'd be chucking away a pretty decent vehicle.

Mark: If you've got a hard issue, the guys to see in Vancouver are Pawlik Automotive. You can reach them on the website You can book right there or you can call them at (604) 327-7112. You have to book ahead. They're always busy. Pawlik Automotive in Vancouver, BC, Canada. Thanks for watching and listening. We appreciate it. Thanks, Bernie. 

Bernie: Thank you, Mark. And thank you for watching.

About the author 

Bernie Pawlik

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