Strange electrical fault!

[danimerebean]

Hi guys!

Got a really odd issue that i'm hoping someone may have come across before.

My car is a 2013 1.6 Mazda 3 Tamura, bought the car privately in April. 2 months later the fault started developing.
The car seemed to struggle on full lock when parking on a drive or supermarket etc. The headlights would flicker and the radio would stutter or maybe reset to the 'Hello' screen as seen when first started. This would happen very rarely and would not happen on demand to demonstrate.
The next symptom is once the car is warm (ie blue icon gone out), when driving on a dual carriageway/motorway with the headlamps on and you indicate to change lane the headlamps will flicker and dim in time with the indicators. The headlamps also dim very momentarily when you apply the foot brake. Sometimes when flashing main beam the instrument lights will light up like a tree and the car will cough but then continue as if nothing has happened! This sometimes also happens when turning the headlamps on while driving.
This has gone a while sporadically but has now got more frequent.
I have drop tested the battery and it passed no problem.
I have checked the alternator output with headlamps on, 12v socket occupied, air con on - 14.5v at idle and 3000rpm
I have checked every earth i can find, even added a thick new one from battery to gearbox!
I had the car diagnostically scanned - It showed battery low voltage, battery high voltage, EC Relay fault code.
Bought a new relay from Mazda - still no joy!

If anyone can suggest a check or share any wisdom i would very much appreciate it!

[Willpower]

Although you say you have checked already, all the symptoms you have are classic earthing problems.  I would suggest revisiting your steps investigating the earthing strips and connections.  Make sure that you have a clean metal to metal connection.
 

[danimerebean]

I've been over the more obvious things like that today after fitting the new relay.

I have just read on a US forum there was a PCM software update for 2013 models presenting with flickering headlights when applying foot brake. Going to give Mazda a call tomorrow to book in for the boot hinge re-call and see what they say about the PCM software.

Fingers Crossed!!!

[StevenRB45]

Have you tried another battery? I know you said you tested it but what you are describing sounds like the voltage is dropping so low when you combine the load of lights and the power steering pump the dash thinks the cars switched off then on again (hence the hello).

[speedy mazda]

I was going to suggest the same steven sounds like  a battery problem  ,is it the original battery ? my lights always dimmed with the  power steering with the original mazda battery.

[moozmooz]

Almost certainly a voltage regulator problem. The alternator output isn't keeping up with demand as fast as it should.

[hanix]

I would think the cheap first option is swap the battery for a known good one. Batteries and car software are sometimes strange bedfellows. (Try owning a Jaguar).

[danimerebean]

Thanks for all the replies guys.

I checked with Mazda UK Technical dept about the PCM update and was as good as stonewalled.
Spoke to a local independent Mazda specialist today and the guy pretty much guaranteed its a Body Control Module fault. Very common apparently. Its a main dealer only job because it needs to be coded - typical.

Tried something new tonight - Reset the ECU, the still with the battery disconnected, removed the BCM. Cleaned all the multi plug pins on the loom and BCM and refitted. Took it for a 1/2 spin when it was dark with main beam, A/C and radio blasting and so far NO FAULTS. Whether this is luck or a fix remains to be seen.

I'll post any updates if it goes sour!

[danimerebean]

Its been a few weeks now and so far so good! Car has run like a dream and behaved itself - until today 

NEW FAULT!

Central locking not working - key fob flashes but the car doesn't lock. When i press the unlock button the indicators flash - how weird.
Interior lights have all stopped working completely
Car says 'Trunk Open' when its not.

All the above symptoms just appeared earlier together when i left work.
If i fix it its being sold ASAP cannot keep chasing faults like this!!

[StevenRB45]

Do the lights flash only when you press unlock or both lock and unlock?

Edit re read first post. My feeling is the tail gate sensor is giving duff information to the BCM telling it a door is open, this disables the locking (just tried it on mine if I leave a door open it only flashes when you press unlock). Does your boot light work?

[danimerebean]

Thanks for the reply, that makes perfect sense.
Took the car to Mazda today for the recall. They phoned me to say the boot wouldnt open, the tech didnt know there was a mechanical opener inside, i had to explain how to open it!

The lights only flash when pushing the UNLOCK button. The boot light doesnt work with the boot open or closed (tried the switch to make sure it wasnt on the OFF position)

[StevenRB45]

I seem to recall reading on honest John there had been issues with the rubber button cracking allowing water ingress into the electric latch. May be worth a look at it, don't know what the car uses to detect if the boot is open though logically it will have a sensor but I can't see it, it's certainly not an old school plunger switch.

[StevenRB45]

Had a play with mine today.

Couple of videos:
https://drive.google.com/file/d/0B62qUAgmdcPddHN4dzE4bjJneU0/view?usp=drivesdk
https://drive.google.com/file/d/0B62qUAgmdcPdbGJSSWlyV2pjRkk/view?usp=drivesdk

My thoughts, the boot light not working suggests the car thinks the boot is shut. The lock button not working suggests it thinks the boot is open. The thing that tells the car if the boot is open or shut is the tailgate latch.

I would imagine there is a Microswitch in the tail gate lock that tells the car what position it is in. In your car it appears the BCM thinks you have shrodingers tailgate (both open and closed).

Do your normal door open functions work? It could be the tailgate switch is faulty but the lack of interior lights suggest perhaps all doors have the same problem but it's only really noticeable on the tailgate due to the electronic release.

To sum up, it could be a Microswitch or it could be the BCM isn't interpreting the signals from the latches properly.

[danimerebean]

Wow great videos thanks, i really appreciate you taking the time out to have a play.

What do you mean by normal door open functions?

[StevenRB45]

When you open a door does the centre screen say door open?