Hello. CX5, 02/2024, 15000 miles. 1. About a month ago, we found the vehicle completely dead because the battery was drained. It had been sitting unused for 4 days. 2. We recharged the battery, and everything worked fine for a few days—until the same thing happened again after the car sat for 3 days. 3. I used a voltage logger (with its own battery, recording voltage every minute) to monitor the battery. Normally, the car goes into sleep mode about 5 minutes after it's turned off, using very little power. It can stay like that for 1,2 or more days, but then, without anyone touching it, it suddenly goes to erratic behavior with periods of wakes ups and sleeps. The power draw increases, which we can see from small drops in battery voltage (see Figure 1). 4. Once, we got a “keyless system malfunction” warning and the start button was blinking, even though both of our key fobs were working normally. Disconnecting and reconnecting the battery fixed it.

Obviously, there is some electronic module inside that erratically push vehicle in some wake up-sleep cycles which drain battery fast.

At a dealership I was told they cannot investigate or fix the problem unless it's actively present at the time of visit. They replaced the battery, but of course it did not help.

Any advice what I can do? Now I'm just disconnect the battery if the vehicle stay more than a couple of days. This is very annoying.
May be I can report to Mazda headquarter department somehow? Probably they have some repair statistics of similar problem?

After 10 hours of normal stay (sleep) some electronics inside goes into wake-up sleep cycles. It drains battery fast.

After about 3 hours of driving the vehicle was OK for 2 days. But any moment it can happen again

 

Welcome to the forum

The dealership is correct that you cannot diagnosis this sort of issue unless the vehicle has the problem at that time you went to the dealership.
You need to leave your Mazda at the dealership for a couple of days and hope that the issue occurs. They will have the hood open to have access to the battery and will monitor the battery voltage drop from stabilized voltage which is about 36 minutes after you turn off the ignition exit and secure the vehcle. After 12 and then 24 -hour period... If more than the specified or normal voltage drop for your exact and specific model Mazda is not within the service voltage range they can then trouble shoot the issue.
Feel good because you Mazda will only be service with this kind of concern from a Mazda Factory Trained and certified mechanic or an independent certified automotive diagnostic Technician.

This is not a usual service issue and there is no TSB as of yet pertaining to this for your model Mazda. However not having the VIN I can't to a complete TSB search and a basic one. Please don't your VIN we are charge for comprehensive diagnostic reports for several platforms and that is reserved for our customers You as the owner could ask your dealership if they could look.

Contacting MAZDA crop direct will yield you pretty much the same answer I did , but maybe less wording... no..... likely less wording.

 

For a static situation those voltage drops are quite high when the activity takes place. Removing fuses and watching is abt the only way you'll get it sorted. Following with interest.

 

Current goes through FUSE 54(25A) "ROOM" and FUSE 40 (15A) "interior" according to this diagram https://www.startmycar.com/us/mazda/...o/fusebox/2024
The current (~3.5A) and fuses are typical for situation when car wakes up (e.g when door or trunk is open). To me the malfunction is arbitrary wake up of one of the modules. I searched TSB, there are no similar for my VIN

 

Ya old school removing fuses is not the proper method to find electrical drains that are abnormal on most vehicles manufactured from at least 2002…..…… …….and definitely Mazda from 2016 to present.

So I highly recommend not to do ot unless you very experienced in diagnostics of electrical system problem solving .

 

No need to get too technical. Fuse removal will point you in the right direction. If you want to get exceptional you can measure the voltage drop across the fuses but that's much more difficult.

 

My first instinct would be to check that the key fob buttons are not getting stuck/jammed and constantly sending signal to the car. There's been times where I noticed a key fob button needed to be snapped in correctly since it was jammed and the little red light indicator was stuck staying on in the fob. If that's not it then I'd unplug anything in the cigarette ports and OBDII port. The USB ports in the arm rest should turn off automatically after a few minutes when the car is shut off. The only other thing I could say is to check that there are no aftermarket things wired into the car, as well as lights staying on in places like the rear hatch when they're not being used.

 

There are a whole host of issues that can cause this.
Personally, a faulty door switch has been an issue for several of my vehicles in the past.
Which is why I always leave the dome light in the "OFF" position on all my vehicles.

As Calisto said leaving it at the dealership, if that is possible for you, will determine the issue.

 

This would also be another good thing to test, along with turning off the rear hatch light.

 

all those are great idea's buttttt.... they would show in a simple diagnostic circuit testing. Presumably Mazda service did at least the basic when the Mazda was initially taken to them and nothing was found out of spec.

Sorry guys but even I have to have customer's leave their vehicles for 2-3 days at a time when looking for mystery battery drains.

you could add water on the top of the battery that touches both terminals at the same time to your list of many possibilities... lol.
Water is a conductor of electricity while in theory I have never had it happen to me or any customer, friend or relative or ever told it happened it's just an anecdotical thought.