Hi all,

2007 STi. I'm having issues with my alarm. Sometimes I lock the car, walk away and in about a minute, the alarm goes off / hazards flash.

I've had a mouse under the bonnet....more seeds and nuts still collecting under the bonnet lining. I wonder if I have a chewed wire somewhere....but this could be a red herring.

The main battery is only a few years old if that, Yuasa. Although I didn't drive the car much a few months ago and it did go flat once, but it jump started straight away.

Possibly related symptoms of a duff battery :

Heated rear window is very slow whilst car is idling on a cold morning, hardly melts frost, then start driving and it works "better"
When I switch my headlights on, the RPM's dip by about 250 - 300RPM and then it stabilises almost instantly....I never used to get this though, normally lights / RPM wouldn't react this way.
Also I have noticed when I first switch the headlights on, they get brighter if I rev it slightly, then they stay bright.


I seem to have lost some bottom end performance too...drives a bit flat then pulls hard at 3.5k RPM
My PSI3 data monitor tells me that the battery is getting between 13.9 - 14.1 volts whilst driving so I guess the alternator is ok. Belt is fine with good tension, no screeches, no battery lights on dash.

Battery terminals are tight, and so is the main alternator terminal.

If I put a volt meter on the battery whilst engine off...what should I see in volts?

Bad earth? I've checked what I think look like earths on the inlet manifold, but there must be others......but as said, no battery light ever on dash whilst driving.

Other history which maybe killed my battery? :
I changed my A/C belt a few months ago, and started the car to check a/c was working. I did this without the alternator belt on, it didn't idle well. Would idling for 20 seconds without the alternator belt kill or at least harm the battery?

 

alarm check bonnet sensor and then door sensors , have volt meter connected as you turn the lights on , check earth connections or just put an extra earth wire on

 

The charging rate on the PSI3 drops to about 13.5 when loaded up with heated rear window, lights, wipers etc.....engine dips quite a lot then picks up again at idle.

Where are the earth leads?
I can see two on the inlet manifold.

The red rubber cap on the alternator has been chewed by a mouse or rat. Bonnet lining now removed.
I'm going to charge the battery up and see what happens, if in a few days the engine is dipping again when loaded with electrics, perhaps my alternator isn't the best.

 

i always stick a spare earth cable on , block to battery negative or to the chassis , voltage sounds ok , are you sure the alternator belt is tight enough , how much rpm drop , it’s normal to drop a bit then back to normal , worth a voltmeter on the battery as you test it under load and see if what you used to test it before is ok , the battery could also be the issue and not working as well as it should even it is getting a full charge , if you have another car swap the battery over and see if it voltage drops or struggles , my maloo is very sensitive to poor end of life batteries , other option get a drop test done on your battery eurocarparts or halfrauds 😁 should be able to do it for you

 

Fingers crossed all it needed was an overnight battery charge.

Charged up the battery last night with my C-Tek charger....up to green 8 on the charger.
Disconnected the charger, engine wasn't started, no load on the battery, and the battery tested at 12.6 volts.

Started the car, no load on the battery with any extra's, battery tested at 14.6 volts.
Engine running, loaded it up with a/c and everything electric, heated rear window (so mirrors too), heater fan speed on full chat, full beam lights, fogs, hazards, even I/C waterspray...everything! and the test reading was 14.4 to 14.5 volts. Didn't use power windows or wipers to be fair - but I think the above was a sensible test load.

Car now drives so much better, and hardly dips when at idle.

I do wonder if just running it for that short time when I did the A/C belt. I ran it for about 20 seconds without the alternator belt on.
Perhaps the battery had never caught up after that or that I have in fact damaged the battery....dark in the morning and evening now, lights, wipers, heated rear window etc. Could be me just being wishful of course!

Time will tell, but for now the alternator seems to be doing it's job fine. The Yuasa battery is just under two years old, so either it's damaged from when I did the A/C belt change job, or, a drain that catches up and overtakes the battery after a while, and a good charge puts in back on par (perhaps only temporarily)

I'm happy now that the alarm issue is separate from the battery issue. I think I just had that in my mind as I've had the alarm chirp when the battery is flat several times now over the last 2 or 3 batteries over the last 8 years!

PSI3 shows BV as 13.9 to 14.2 volts when driving along, and hardly changes when I load up electrics driving along.....for now. Idling is the real test, so I will keep testing periodically for now. At the moment with my results, if I replace anything it will be the battery.

How do I check the bonnet alarm trigger? I can see it of course, but how do I inspect it?

 

Hopefully issues solved , push the bonnet button down arm it give it 30 seconds or so then take your thumb off it alarm should go off