Electrics gone mad!

B

B300ABT

Member
The electrics on my TDI seem to have gone mad.
First off, the alarm took to going off seemingly randomly, but it occurred to me that it started to happen when it had been a cold night.... and generally at about 7 in the morning!
Then I found out that whenever I unlocked the car ( I only use the key, fob battery is dead), the interior lights flashed like mad, but went out when I started the engine.
Following that, I realised that in addition to the above, the other doors of the car, including boot and fuel flap, wouldn't unlock, and nor would the electric windows operate........ until I'd been driving for about 20 minutes or so.
So far my only action has been to disconnect the siren..... and that's quite a challenge in itself!
Anybody got any ideas as to how I fix this properly?
Thanks in advance
John
 
This sounds like a classic case of (in)convenience control unit failure - this is the black box you see when you open the passenger footwell and it controls all the features you mention.

Replacement is physically straight forward, althoiugh you will need to have the unit coded to the car and the keys re-matched as well. A new unit costs around the £220 mark from a dealer.

Cheers,

Mike
 
Thanks Mike...... needless to say I had guessed it was going to cost a few quid to fix! I think I'd already been told that a replacement set of keys was going to cost me £150.
Modern electronic controls are an absolute nightmare once they start to go awry some years down the line. Porsche 928 is a classic example: Car of the Year in 1977 or '78, and now the majority of them are being sold for buttons because hardly anyone has a clue how to deal with their electronic systems, and many of the main units are no longer available from Porsche.
 
I used to have alarm randomly going off (mostly on rainy days). Then my battery's voltage dropped significantly over the first cold snap this year. There was engine cut-out and lights dimming. I've since replaced it and I've never heard the alarm going off since.

I can't say i'm sure, but could it be your battery running a bit low on voltage? Wouldn't hurt to give it a quick check.
 
It is my turn!

I can hardly believe it! I last drove my car on Sunday. It wasn't motorway but it was a good drive on 40/50mph roads for about 1hr in total. Tonight, I want to go out, took the key and nothing was responding. Thought Keyfob battery died, tried second key, same. Used the mechanical way to open the driver door, then WOOHOOO! Alarm goes off, dot matrix dashboard flashed the engine oil sign, power steering sign and a yellow sign I've never seen before nor can I see in the manual. It looked like a wing mirror with a + sign in the middle with arrows on top and bottom (?). Anyway, the alarm was not stopping, remote had no effect. I even started the engine, alarm was still on. Central locking all dead still. I had to at least stop the alarm noise, so grabbed my screw driver, popped the emergency boot release and unplugged the battery!! Phew!

Quickly measured the battery voltage, 12.26V... This seems low, as low as the OE battery when I had engine cut out. I then reconnected the battery, central locking back on, disarmed the alarm, a couple of signs on dashboard still. Started the engine, things started to settle down. Voltage is at ~13.9V when engine is idle. Gave it some gas ~2000rpm, goes to 14.1V, turn off climate, 14.2V. Back to normal-ish. Then drove for 15mins, stopped, engine off. Couple of beeps as if I didn't switch off the lights, but I did. Power steering sign again. Started the engine, drove another 15mins, keeping revs at 2krpm+. Seems to be ok now.

The car has a 2 months old Lead Calcium (more ££) battery from Halfords when I last had battery problem. Here are my questions:
1. 12.26V, that should be low? I remember it was 13.8V when my old battery was fine.
2. idle voltage of 13.9V, is this normal? Alternator problem?
3. Engine running rev voltage of 14.2V, this is fine right? Should rule out alternator?
4. Does this still sound like a battery issue? or I have a faulty CCU?

I'll see how it goes tomorrow. At least I have the receipt of the Halfords battery. May be I should get them to battery test it.
 
Sounds like the battery not holding charge to me Humps - not a massive fan of Halfords tbh - Angie had one in her Yaris that lasted about 3 months before we took it back and swapped it out for one that now seems to be working properly.

I'd take it back to them - don't the calcium ones have a 3 or 4 year warranty?

Cheers,

Mike
 
Hi Humps,

After having plenty of battery problems recently I found this table useful. The Open circuit voltage you are seeing suggests that the battery is 50-60% charged. If you have a smart charger such as a ctex 3600 or Optimate 4 then try this, as it will recover the lost "sulphided" charge capacity. Sometimes if the battery sits on the shelf a long time the lead plates react with the sulphuric acid to form lead sulphide. Only a smart charger will recover this sort of thing. An old fashioned charger will try an charge the battery but will end up putting in more than 14.4V, which will result in the battery acid decomposing and bubbling. But it will never recover the lost capacity.

Open Circuit Voltage / Approximate charge / Relative acid density
12.65 V / 100% / 1.265 g/cm3
12.45 V / 75% / 1.225 g/cm3
12.24 V / 50% / 1.190 g/cm3
12.06 V / 25% / 1.155 g/cm3
11.89 V / 0% / 1.120 g/cm3

If the car has been running recently then the battery voltage you measure will be masked by surface charge (hence your 13.9V reading), the best way to get the real voltage of the battery is to warm the glow plugs a few times, without starting the engine, or put the headlights on full beam for 3-4 mins without the engine running (this is what the RAC man did when coming to fix my car!!).

I put my A2 on the charger every month of so just to keep it in tip top condition. I would recommend the CTEX 3600, very easy to use and powerful enough to recover the 80Ah OEM battery on the A2 with ease.

But as your battery is only a few months old I would take it back, but a Smart charger is the best way to look after your battery, especially in my case since the car does lots of short trips. I also have is permanently connected to my MX-5 in the garage during the winter.

Cheers,

David
 
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