My 2015 Mazda 3 sat unloved for a little too long during a quiet Covid winter, but after re-charging the battery I had the following electirical issue.

The car started, and I drove it for 45mins, and on return home I put car into park, pressed Stop/Start button, and the infotainment did not switch off, and when leaving the car it would not electronically lock. It just beeps with the red flashing light on dash that looks as though there's someone in the car or a key left inside.

The battery was the original, and a mechanic recommended getting it swapped, so I took it to get battery replaced. After new battery was installed the engine could be turned off, everything shutdown as expected, I could leave the car and it would lock electronically without any issue. I repeated this several times.

Now after one week the original issue has returned: the car starts but it will not switch off infotainment and will not lock electronically. I can lock with the key that comes out of the fob, but I need to fix the problem. The infotainment being on will just drain the battery again (I've turned brightness down as much as I can).

I cannot find anything in the manual about a procedure to follow after changing the battery. If it was circuit or fuse related, then I cannot understand why it was all fine immediately after the battery swap but not now.

Any advice greatly appreciated.

 

Get it scanned for fault codes. Also while its being scanned get the live data inspected for gear position switch operation.

 

Yikes....that's scary! When you recharged the battery, you didn't have it still connected to the car, right? Stuff is controlled so much, these days, by the computers I'm suspecting an ECM but a good scan should show which one is malfunctioning. (Pray it's not one of the major ones...that's big bucks.) To stop the drain you could, of course, disconnect the negative terminal from the battery when done driving but that's not really safe because you do get a power surge doing that, which computers don't like.

 

Thanks for responses.
Battery was disconnected from car when we used a plug-in charger.
The brand new battery eventually drained due to the core issue of car not switching off properly. This weekend, I disconnected battery from car, and gave it another little top up, enough to get the engine going. Did a 40min drive, came home and car switched off and locked fine. Done another 20min drive today and still behaving.
I've got a code reader, but it's not showing any faults - but then the problem seems to have stopped for now, and I don't know if disconnecting battery would reset any historical logs (?) but the reader is not showing any codes.

What's frustrating is that this now seems to be intermittent and I don't have a lot of trust the problem won't reappear.

Is it possible this could still be a blown fuse?
Can I use a home scan-reader to check the active gear position?
Any other ideas?

I seem to be stuck with either trusting it and hoping it won't fail again, or taking it to a Mazda dealer who are likley to say it's operating normally.

 

I have heard of an issue with Mazda's called a parasite drain....do a google search and you'll see tons of info.

Is your car still under warranty? If so, definitely go to the dealer with it. Mazda may already have a fix for it in one of their TSBs (technical service bulletin). Again, the dealer can look up your VIN and see if it has any and also any recalls.

I thought I saw a video on this problem....I did! Watch Scotty! (One of my favorite youtube mechanics)

 

I talked to my Dad yesterday about your parasite power drain issue. (He's a retired machinist...worked 40+ years in a paper mill). Anyway, he asked if you'd had anything installed in your car recently like an alarm or radio or anything electrical. Folks sometimes can connect to a hot wire instead of a wire that's only hot when the car is on and that would drain the battery. Also, he told me about an Avalon he bought years ago and it was brand new but if he let it sit longer than a few days, it would have a hard time starting...like the battery was being drained. He brought it back to the dealer and they tested the battery/alternator and both were fine. But it kept doing it and then left it alone for a week and a half and it wouldn't even start. Toyota replaced the battery but couldn't find the cause. It took a while but they FINALLY discovered the connection in the rear trunk, that turns off the trunk light when you close it, wasn't working. So the little light in the trunk would stay on the whole time. No big deal if you drive a lot (the batter will recharge) but if you let it sit for a week or so, even a small light will drain the battery down.

He also suggested you keep a little battery jump starter in your car until you find the issue. Jumper cables can be dangerous with so many electronics in a vehicle these days but this new little things really work. https://smile.amazon.com/Audew-Start...xpY2s9dHJ1ZQ==

 

For the record, a follow up on my issue..

I knew what was draining the battery - it was that the infotainment wasn't turning off - so the root cause was that the car wasn't shutting down properly.

The suggestion from grim_reaper sounded possible, although I didn't manage to find a way to confirm the gear switch position on my fault code reader when the problem was present.

What I did do was try to replicate the problem by having car in Drive (this being an auto) and attempted to turn car off with the stop/start button. This gave the same symptoms as my problem - the engine turned off, heads-up display went down, but the infotainment stayed on and the car would bleep when being locked with the red flashing light on dash. I don't know if this was in any way a valid test, but it did produce exactly what I've experienced before, so the theory about the car believing the gear switch was still in Drive when it was actually in Park sounds plausible. It would explain why there is no background electrical/fuse issue - since it would sometimes behave normal, lock fine and not experience any drain.

Anyway, I've been driving the car for the past couple of weekends, including a couple of long journeys, and the problem has not been recurring. For about the past dozen journeys the car has switched off fine exactly how it should. Not sure I yet have full confidence it won't return. If it was a gear switch position problem, not sure why that would appear and disappear, maybe a long period on non-use doesn't do a car any favors but still odd.

I'll try to do a follow up report in a couple of months to (hopefully) close this off!

 

Sounds like you're on the right track! Have you checked with Mazda for any computer updates available? Last year, my Tundra ETune Audio system was periodically rebooting for no reason or just turning itself off but the most annoying error was the Bluetooth kicking me off my phone when making a phone call. Toyota has a download site where you download the patch onto a thumbdrive and run a software update...took a few tries but worked great and it was free.

 

I found this on another website, for a Mazda 6, but symptoms are same as for me.
https://www.mazdas247.com/forum/inde...ark.123870451/

I'm hoping it's just that the park position sensor wasn't working properly after a long time of non-use, and it will just go away! Fingers crossed...