Not starting even with new battery and starter, seems to have lost TCM communication

rickdsac

Member
The vehicle I have is a 2015 Mazda CX-5 with about 100k miles on it. It was running fine until the other before the following:

I used the CX-5 to jump my Dodge ram truck which had a dead battery. I didn't drive the CX-5 then for a day or two and when I went to start it, it seemed the battery was dead, I think I needed to drive it around a bit after giving the jump.

I then tried to use my truck to try jump starting the car but it wouldn't work.

Since then I have replaced the battery and had a new starter put in by someone who came out to my house but it does not start.

There is a code: U0101 which seems to have something to do with not being able to communicate with the TCM.

The vehicle powers on fine as far as the dash, etc. I took the videos below to show what happens when I try to start it:

video 1: When I get into the vehicle and touch the brake with the key fob inside the vehicle, the key light is solid green, which I think means it is successfully detecting the key fob: https://www.youtube.com/watch?v=E1X96vWV9gM

video 2: This is a video of the dash when I am pushing the keyless start button with the key fob inside the vehicle: https://www.youtube.com/watch?v=QvKDft2MYbQ

video 3: There is some kind of noise that happens during the same time as video #2, I put my camera under the vehicle to record it: https://www.youtube.com/watch?v=nJdzJOjYqsk&feature=youtu.be
 
is it possible you reversed polarity when you jump started the other vehicle

Sure sounds like it...

I would closely inspect each of the fusible links on the battery POS + terminal. And then the fuses in the engine bay.

Hopefully you kept the old battery and starter, as they are not going to be the issue.
 
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I agreed it sounds like polarity EXCEPT, if I'm not mistaken, the car wouldn't have been able to jump the other car. So he would surely know he did that
 
I agreed it sounds like polarity EXCEPT, if I'm not mistaken, the car wouldn't have been able to jump the other car. So he would surely know he did that

Exactly right. If he had reversed polarity, not only would he have gotten a spark show but there's no way that his truck would have started in that condition.
 
Exactly right. If he had reversed polarity, not only would he have gotten a spark show but there's no way that his truck would have started in that condition.

Yes, but you are talking about jumpstart#1, I am thinking the polarity issue may have occurred on jumpstart#2, when he was using truck to jump cx5.(coffee)
 
I agreed it sounds like polarity EXCEPT, if I'm not mistaken, the car wouldn't have been able to jump the other car. So he would surely know he did that

If he/she made the mistake of hooking the cables up backwards on the first attempt to jump the other vehicle it could be the case or also if after attaching the clamps to the cx-5 battery, he/she then accidentally touched the other end of the jumper cable clamps together. Either of those would most likely fry the ECU or other electronics of the vehicle.

It just seems like too much of a coincidence to have the issue right after the jump starting
 
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If he/she made the mistake of hooking the cables up backwards on the first attempt to jump the other vehicle it could be the case or also if after attaching the clamps to the cx-5 battery, he/she then accidentally touched the other end of the jumper cable clamps together. Either of those would most likely fry the ECU or other electronics of the vehicle.

It just seems like too much of a coincidence to have the issue right after the jump starting

Now that I think about it, yes this did happen: "he/she then accidentally touched the other end of the jumper cable clamps together. ". I didn't think much of it at the time but now it makes sense. I should have been more careful I was in the middle of doing a bunch of repairs on my house when I went to do this so I was pretty exhausted and not being careful enough.

So it seems, then, that it did fry the ECU or other electronics. Is the cost to replace these pretty significant?
 
Now that I think about it, yes this did happen: "he/she then accidentally touched the other end of the jumper cable clamps together. ". I didn't think much of it at the time but now it makes sense. I should have been more careful I was in the middle of doing a bunch of repairs on my house when I went to do this so I was pretty exhausted and not being careful enough.

So it seems, then, that it did fry the ECU or other electronics. Is the cost to replace these pretty significant?

It should have blown one of the many fusible links that are located on the battery POSTIVE + Post, or a fuse in one of the fuse boxes, either under the hood or inside car. Have you inspected all of these?
 
I did inspect them and didn't find any blown out but maybe I missed one, I will check that again now, thanks.

Yes, check all carefully, I wish I knew the exact ones to tell you to check... There was a previous poster here NYC if I recall right, who also had an issue after a jump start accident, and it was either a fusible link or fuse...
 
Something similar happened to me (many years ago) when installing a battery that had the terminal posts reversed compared to the OEM battery posts. A very large fuse blew, preventing any further damage to engine electronics. Swapping the fuse was a piece of cake, thankfully.
 
Thanks everyone, it was a fuse, I must have missed it when checking last night, it seems to start now. I will find out if the starter was actually bad too when I take it to the auto repair shop so they can test it.
 
Thanks everyone, it was a fuse, I must have missed it when checking last night, it seems to start now. I will find out if the starter was actually bad too when I take it to the auto repair shop so they can test it.

WOO HOO!

For future reference, so we can help others, where was the blown fuse located.
 
This is good news. that said, anyone know where we can get a cheap fuse tester?
 
Thanks everyone, it was a fuse, I must have missed it when checking last night, it seems to start now. I will find out if the starter was actually bad too when I take it to the auto repair shop so they can test it.

Occam's razor.
 
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