2018 Mazda CX-5 Various Electrical Issues

[CycloneCX5]

TLDR: Lift gate, infotainment screen, head up display, key less entry, keys, heated seats, heated steering wheel, interior lights, USB’s, and trip monitor stopped working suddenly. Car runs fine. Battery checked multiple times and showed to be “good”, and no fuses appear to be blown.

I have a 2018 Mazda CX-5 Grand Touring AWD. About two weeks ago the lift gate started to intermediately not want to open and give 3 beeps. It would not open with the key, rear button, or driver side button. Disconnecting and reconnecting the battery would temporarily fix the issue or over time it would decide to work on its own, but it kept returning.

A week after this started, I got a check engine light and took the car to O'Reilly to get the codes checked and to get the battery checked. The codes were U0100, U0115, U0121, and the battery and alternator showed good on the tests with the battery installed in the car. The check engine light would go away and come back randomly it seemed.

Several days later it all got worse. The lift gate issues persist but now the infotainment screen (tried back+nav+mute but nothing happened), head up display, key less entry, keys (not responding to both keys and have to place them next to start button to start the car), heated seats, heated steering wheel, interior lights, and USB’s in the console don’t work. Also the trip monitor resets after each drive. I took the battery out of the car and got it tested again at O’Reilly and the battery tested good again, it is an Optimum RedTop that is 2.75 years old. I tried checking all the fuses in the engine compartment and under the steering wheel and didn’t see any that looked bad.

The car seems to run fine otherwise. I just have to unlock/lock the car with the physical key.

Does anyone have any idea what could be causing all of these issues?

 

[Moonlighter]

If possible I would try a different battery. This still sounds like a dodgy battery or a bad connection to me.

i assume that you checked the battery cables for corrosion and cleaned and TIGHTENED the lugs when you put the battery back in?? They need to be bright and shiny and TIGHT.

How old is the fob battery? If any doubt its cheap to put a new one in there.

 

[Ranman57]

Just a long shot here but any chance you have critters under the hood chewing wires? Happened twice to a step-daughter's Ford SUV, car ran both times but all sorts of bizarre electrical gremlins appeared.

 

[Mazdiod2]

It might be something unusual, critters are a possiblity, as this is the time of year they plan invasions.
Maybe a bad ground somewhere important, as all of the codes refer to various communication modules.
Do you drive through deep water on the way to work?

 

[N7turbo]

Just a long shot here but any chance you have critters under the hood chewing wires? Happened twice to a step-daughter's Ford SUV, car ran both times but all sorts of bizarre electrical gremlins appeared.

It might be something unusual, critters are a possiblity, as this is the time of year they plan invasions.

My Dad had a squirrel chew through his Lexus wiring harness, so yeah.

Also it's possible one of the CAN bus modules went bad. I would see if those functions all route through the same module. I know this isn't Mercedes, but they are a known failure point on those cars. Especially when water leaks in...

 

[SparkYellow]

When my CX-3 developed electrical problems (different from yours) this May, I looked up the codes and searched broadly for anything that is remotely relevant. One thing that came up was the ROOM fuse for a different model and set of symptoms. I swapped it out and the codes went away. I also cleaned the terminals and replaced the 2-yrs battery because it was leaking.

It could have been a lot worse, rodents are active at my weekend getaway spot.

When dealing with fuses and relays, I swap them out if I can find a new replacement. I understand that they may still be healthy. But I know folks who punch in at work on time and do nothing.

 

[CycloneCX5]

If possible I would try a different battery. This still sounds like a dodgy battery or a bad connection to me.

i assume that you checked the battery cables for corrosion and cleaned and TIGHTENED the lugs when you put the battery back in?? They need to be bright and shiny and TIGHT.

How old is the fob battery? If any doubt it’s cheap to put a new one in there.

Thank you for the reply.I have thought about trying a new battery, I just haven’t wanted to commit to buying a new one yet, but that might just be where it goes.

When we removed the battery we noticed some corrosion around the positive terminal. Cleaned both battery posts and the connectors, applied battery terminal grease, and tightened the connectors on securely.

I FOB batteries are less than a year old. Tried putting a new one in one of the FOBs and it didn’t help.

 

[CycloneCX5]

Just a long shot here but any chance you have critters under the hood chewing wires? Happened twice to a step-daughter's Ford SUV, car ran both times but all sorts of bizarre electrical gremlins appeared.

That is something we didn’t think about. We tried examining all the wiring we could in the engine bay and under the steering wheel. Did not see any wiring that looked damage, or any signs of rodents. Thank you for the idea.

 

[CycloneCX5]

It might be something unusual, critters are a possiblity, as this is the time of year they plan invasions.
Maybe a bad ground somewhere important, as all of the codes refer to various communication modules.
Do you drive through deep water on the way to work?

I have not driven through any deep water in this thing. We have tried to check every ground to make sure it’s secure and looks right. So far all the ones we have seen appear normal.

 

[CycloneCX5]

My Dad had a squirrel chew through his Lexus wiring harness, so yeah.

Also it's possible one of the CAN bus modules went bad. I would see if those functions all route through the same module. I know this isn't Mercedes, but they are a known failure point on those cars. Especially when water leaks in...

I will try to take a look at this, given some of the intermittent failures it seems like it could be a module failing. That is a good idea.

 

[CycloneCX5]

When my CX-3 developed electrical problems (different from yours) this May, I looked up the codes and searched broadly for anything that is remotely relevant. One thing that came up was the ROOM fuse for a different model and set of symptoms. I swapped it out and the codes went away. I also cleaned the terminals and replaced the 2-yrs battery because it was leaking.

It could have been a lot worse, rodents are active at my weekend getaway spot.

When dealing with fuses and relays, I swap them out if I can find a new replacement. I understand that they may still be healthy. But I know folks who punch in at work on time and do nothing.

That is a good idea. I will see if I can get my hands on any relevant relays, and try some new fuses.

 

[SparkYellow]

That is a good idea. I will see if I can get my hands on any relevant relays, and try some new fuses.

Can you also test swapping out the room fuse just for fun? There should be a spare fuse in the box.

 

[CycloneCX5]

Can you also test swapping out the room fuse just for fun? There should be a spare fuse in the box.

WHAT IS THIS FUSE POWERING!?

I looked at the fuse and it was blown. I replaced it and everything seems to be working fine. I will update tomorrow if everything continues to work well. So far it looks like that room fuse is the root of all my problems.

 

[N7turbo]

I will try to take a look at this, given some of the intermittent failures it seems like it could be a module failing. That is a good idea.

I'm looking up wiring diagrams but am having some trouble finding what I'm looking for. I've done this for a Mercedes. The idea is that there are 2-5 modules (sort of like a router or switch in computing) where everything plugs into, so if the module fails, a whole group of items will stop working.

Edit: just saw the above post. Hopefully it was just that simple.

 

[gobroncos]

WHAT IS THIS FUSE POWERING!?

I looked at the fuse and it was blown. I replaced it and everything seems to be working fine. I will update tomorrow if everything continues to work well. So far it looks like that room fuse is the root of all my problems.

2018 online manual says “overhead light”. 2025 online manual says “for a protection of various circuit”. Based on your experience and other’s experiences, I’m guessing it’s always been more than just the overhead light.

 

[RedBaron]

I went through the schematics for my CX-50 and tracked what every fuse powered. Obviously, this will not be the same for the CX-5, but just to give you an idea, the room fuse covers the following for the CX-50. Yep, a lot of dissociated things :

15A

Room light

Active driving display (B+); Remote start; Seat posn memory ctlr; EPB/Hold parking indictr; Shift indictr; Map/mirror lights; Power liftgate ctlr (B+); Sunroof switch; Autodim Homelink;