I think my ECU got fried, can anyone confirm?

So I installed a the Mazda Mobile Start this weekend. Everything went fine. Car started perfectly and all functions worked fine. So right before I buttoned everything up, stupid me pulled out the connector to the ECU while power was still applied to the battery (car was off) as I was just inspecting the various connectors on the passenger side.

Now my car will not start up and I suspect it was because of that action. When I go to the driver side to start the car up, foot on the brake, push the ignition button... the engine fails to start. The display cycles through various messages:

• Keyless System malfunction
• Blind Spot Monitor malfunction
• Smart City Brake Support malfunction. Forward SCBS Disabled.

I have a 2016 Mazda CX-5 GT. The PN of the ECU is: PE1B-18-9R0R.

I tried disabling the battery several times. going back and making sure the connectors were plugged in good.

I'm guessing I'm going to have to replace the ECU, but figured I'd toss this out here to see confirm and see if there is anything else I should try. Any body replaced an ECU before? Is it simple plug and play?

Did you have a key in the car? Check the status of the key light in the instrument panel against the error codes in the operators manual and it will give you an idea of what is wrong.

Just take it to the dealer and feign ignorance and hope they fix whatever it is under warranty... don't give them any clues of your idiocy

I did take it to the dealer this morning. Turned out that my battery was dead... really dead. I must have left the dome light on overnight. The battery was my first reaction. The car wouldn't jump. When I put it on my 6v/12v battery charger that I use to condition my motorcycle for 1-2 hours, it read 75% so I assumed the battery was fine. It was either so dead I wasn't getting a good reading, or the charger is crap when it comes to analyzing the battery level. Luckily I had AAA for the towing.

Also, the dealer said the unit on the bottom passenger side couldn't be the ECU. I'm not sure what it is/does, when I look up the p/n, it just says control module.

The ECU is inside a plastic body near the battery. Also that looks like a DENSO ECU so it's supported by ECUTek and you have good ECU tuning potential.

bgibson said:

⋯ Luckily I had AAA for the towing.

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You don't need AAA as your 2016 CX-5 does have free 24-hour Roadside Assistance covered by Mazda. (whistle)

So did Mazda dealer recharge your dead battery and things went fine? I thought you said car started fine right before you wrapped up? And then the battery suddenly died? If you only unplug the connector, there's almost zero chance to damage a module even with your battery connected.

the fact that he left the battery connected while installing the remote start tells me that the dome light was on or other stuff was on the entire time, draining the battery
the manual/instructions says to disconnect the battery before even touching anything electrical in the car... it still baffles me why so many people don't even do that and then things get screwed up afterwards because they didn't

Disconnecting the battery is always recommend, but I rarely do and have never had any issues.

Most of those alarms are due to disconnecting a battery, there is a list of things that need reinitializing after battery disconnection.

yrwei52 said:

You don't need AAA as your 2016 CX-5 does have free 24-hour Roadside Assistance covered by Mazda. (whistle)

So did Mazda dealer recharge your dead battery and things went fine? I thought you said car started fine right before you wrapped up? And then the battery suddenly died? If you only unplug the connector, there's almost zero chance to damage a module even with your battery connected.

Click to expand...

Thanks for the tip on Roadside service. I had AAA before my Mazda purchase and held on to it for travel discounts and such.

I should probably clarify what I did. I did remove power from the vehicle and followed the directions to a "T". It was at the stage where you need to register your starter with the car when I re-connected power to the vehicle (after all wiring was done). This was most likely when I turned my dome light on. I completed the registration and was able to start my car through the mobile app. It being Saturday night, I called it a night and planned to put the trim pieces together Sunday morning. So I suspect the battery drained real good over night.

Sunday as I was putting everything back together, I was poking around a bit. I wanted to take picture of connectors while I had everything out to evaluate replacing my head unit. That's where I got stupid and didn't disconnect power as I was unplugging connectors in and out.

After I was done screwing around, I put all the trim panels back. This when I found out my car wouldn't start. I knew it couldn't have been the starter since it was only a 2-wire hookup and it worked the night before and I haven't touched it since. My first instinct thought that it was a dead battery. It wouldn't take jump start. I hooked it up to a battery charger. I waited a couple of hours for it to charge. My charger mis-read the battery and thought I was at 75%. This is when I thought I may have done something really bad. Especially when I was getting very weird messages and none of them included anything about the batter being low. Hindsight, I should have just plugged the battery back in the charger and let it sit overnight.

So, on Monday, I towed it to the dealer. They later came back out and told me the problem was the battery was dead. They let it charge up a few more hours before the let me leave. I haven't had any problems since and haven't noticed any draining issues.

So lesson learned. I'm just glad it was the battery and not something worse.