Alarm issues after flat battery

[James_T_Kirk]

Hello - back story, I’ve not started the car since before Christmas and hence a flat battery. Never had any issues with the car before this.
2003 TF 135.

My new CTEK charged my flat battery no issue. Great piece of kit. Now when I use the fob to lock the car after a few moments the flashers flash (alarm sounder/horn is unplugged to not annoy anyone). I can lock and unlock with the key or fob but using the fob sets the alarm and then after a few moments it activates the flashers (and horn I guess if it was plugged in).

I initially thought it was because I had the charger attached but I’ve removed it now.

So what gives? Following the flat battery and subsequent charging do I need to reset the alarm? Note, I also disconnected the battery leads whilst I fitted my CTEK comfort charger leads but considering the battery was flat I figured this would make no odds.

[Notanumber]

Have you used the Search function on the 3 different forums that you have posted the question on ?

[James_T_Kirk]

Yes.

[nigelandjo]

Have you pressed unlock 5 or more times to resync the fob? Have you tried the spare fob?

[Charless]

Interesting but I only have experience of Fs so for my tupennyworth:
Can the car be started and driven normally?
What happens if you lock the car with the key?
Do you have a multimeter, what is the (recovered) battery resting voltage? Does the alternator charge normally?
If the operation of the locks caused a voltage drop in a weakened battery it might trigger the alarm.
Microswitches in door locks can give up at any time.
As the response sounds immediate it might be the ECU needs resynching to the immobiliser.
Pscan or a T4 analysis might throw up what is triggering the alarm.
Good luck and do let us know when you crack it.

[Geoff.F]

Cetec will float charge to maintain a charged battery but not a flat battery. You need a “Proper charger”
A voltmeter will show any voltage drop due to a dirty connection if you know how to use it.

[Notanumber]

If you only have a modern charger the work around to make it charge a flat battery is to run jump leads to a spare car battery which has some charge in it. The charger will work. After an hour or so remove the jump leads and it will continue charging your battery.

[James_T_Kirk]

I've ben thinking about it a bit more and maybe its just a coincidence that the alarm issue showed up at the same time as i let the battery go flat. I initially figured that allowing the battery to go flat caused the alarm issues but maybe i have an existing alarm issue thats not related.
So tomorrow (if it ever stops raining) i'll recheck the battery (my new CTEK which i really like will confirm if i have full battery power) and see if i can isolate the issue.
Some have suggested door switches, others have said it may be the left-hand side boot wiring.

Just one more thing i think is prudent to mention is that since charging the battery i have not started the car yet. When i checked the charge state it was getting dark, rain was imminent so i just locked it with the key and put the cover back on (last Monday).

[James_T_Kirk]

Thank you for all the great information.

[James_T_Kirk]

Good news, it stopped raining for a bit on Sunday so i whipped the cover off and started the car (not started it since charging the battery remember) and what do ya know, its all back to normal. Dunno if starting the car has any impact on resetting the alarm/immobiliser but i have plugged the alarm sounder/horn back in and it sets as it should, On pressing the lock part of the fob the red LED on the dash flashes furiously for a few moments (whilst holding my breath) and then settled down to a slow flash (and breath).
On a general note, i let her warm up, took her for a spin, water temp gauge just below halfway, oil temp was about 90 (hard to tell on that gauge) and radiator cooling fan was coming on and going off correctly.
So spring is in the air, all is good in the MG TF world.
Sticky throttle next....

Oh, almost forgot, to my forum stalker, i will be posting this in all three forums that i normally post in.
To the other helpful forum members, thank you.

[RobboMC]

All modern cars like to have that power supply close to 13 volts.

I had a flat battery in my Captiva last week; it's taken 3 days for me to get the Bluetooth from the phone to reconnect

So I have given up and driven the F to work

[Charless]

Good result James. Sticky throttle should be easy to check but probably means a new cable which is a bit more involved; but doable.

[Reckless Rat]

My 'F' still has sporadic issues with the alarm. Sometimes when I lock it, it's fine other times it goes off after a minute or so. I have got to the stage, after messing with the boot lid wiring loom on several occasions that I just don't bother locking the car any more. There's nothing inside it worth nicking anyway and they'll never get it started without the key and the blipper.

Fingers crossed!

[Bikibob]

2004 TF I charged the battery and it is reading 'full' and more than 12v. Insert ignition key and turn to start the car it lights the dash warning symbols but wont go through to turn the engine and there is a waring noise high - low not very loud.
I suspect the alarm system has locked/disabled the starter. Help please.

[nigelandjo]

It sounds as though the immobiliser isn't fully disabling. Have you tried the spare fob?

[Bikibob]

Neither fob will lock the car - suspect they need new batteries for them - is that an easy fix. I can lock/unlock the car using the key.
I have tried your five times on off trick. Problem remains - frustrating.

[nigelandjo]

Worth trying a new battery ~ clearly if the battery is dead it won't work. Easy to switch the battery, the old one just slides out once you have the fob apart. Then you need to resync it to the car by pressing unlock 5 or so times.