Dead short?

Nimby

Distinguished Member
Hi

I went to start the car after a week without motoring. Not a sign of life. Not even the clock! I checked the battery with a DMM and it read 1.2V.

I removed the positive clamp and the battery then read about 11V.

The car was a recent purchase and it was dead flat when it should have started at the dealers.

They used jump cables and it started. I test drove it, bought it and took it home.

Then it needed a new battery because it was flat again the very next day despite a good run.

I'm still within the dealer's guarantee but he's miles away and not likely to make a house call.

What should I be looking for? This has never happened to me before. No lights were left on. I am very careful about that.

BTW It's a '96 Corolla 1,3.

Thanks for any advice.
 

Trollslayer

Distinguished Member
If the battery is on the way out and losing charge it may have trouble with all the systems drawing power when connected - clock, remote locking, etc..
There is quite a lot now and frankly if it didn't start at the dealer on it's own then I suspect you will have to replace the battery because you accepted it in that condition.
 

Nimby

Distinguished Member
If the battery is on the way out and losing charge it may have trouble with all the systems drawing power when connected - clock, remote locking, etc..
There is quite a lot now and frankly if it didn't start at the dealer on it's own then I suspect you will have to replace the battery because you accepted it in that condition.

Thanks, but it has a brand new Varta battery.
 

IronGiant

Moderator
Either there is a bad connection (hence the difference between 1.2V and 11V) or, and I suspect this is more likely, the alternator has packed up. Any motor accessory dealer should be able to test it for you and tell you if the alternator is knackered.
 

Nimby

Distinguished Member
Either there is a bad connection (hence the difference between 1.2V and 11V) or, and I suspect this is more likely, the alternator has packed up. Any motor accessory dealer should be able to test it for you and tell you if the alternator is knackered.

Thanks, I'll get the alternator checked. I have to get it going first to be able to reach a dealer. I have an emergency starter/charger but I haven't used it for several years. I'll leave the device on charge overnight then try starting the car tomorrow. The car seems fine when it's driven more regularly.

I must admit to being confused by the very low connected voltage. I thought at first there must be a drain or a blown fuse. But such a low reading suggested a short.

The battery terminals are clean and the clamps look as good as-new. I removed them and replaced them just to check.
 

IronGiant

Moderator
Not sure, but it could be shorting out through the alternator if that is the problem.
 

Thug

Moderator
Check the earth wire too.
You said you checked the battery clips, but the wire has another end to it, that is either connected to the engine or the body work. Take that off and give a good clean too.
I suspect the alternator though, but usually if that is faulty it will effect the running too.
 

Nimby

Distinguished Member
Check the earth wire too.
You said you checked the battery clips, but the wire has another end to it, that is either connected to the engine or the body work. Take that off and give a good clean too.
I suspect the alternator though, but usually if that is faulty it will effect the running too.

Thanks. I'll check the earth strap connection next.
 

Nimby

Distinguished Member
Thanks. I'll check the earth strap connection next.

O.2 Ohms between the battery terminal and the head.

I hope it's not the alternator. £160 new even if I fit it myself.

I could see if the dealer will go halves. It was a known fault at purchase. :suicide:
 

Nimby

Distinguished Member
Not sure, but it could be shorting out through the alternator if that is the problem.

I have been searching around the very low voltage reading. Apparently a duff diode in the alternator can cause a short. I had never heard of this before. I hope you are wrong but it looks increasingly likely.

Thanks.
 

IronGiant

Moderator
If you go to motor accessory place you can usually get a refurbished exchange alternator in exchange for your knackered one for much less than the price of a new one. I assume you can still do this... By less I mean very much less...
 
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Nimby

Distinguished Member
If you go to motor accessory place you can usually get a refurbished exchange alternator in exchange for your knackered one for much less than the price of a new one. I assume you can still do this... By less I mean very much less...

Thanks. Not sure this is available over here. I haven't needed anything so have never asked.

There is a used parts service available from car breakers. It's a popular car so there should be plenty of spares about.
 

jasonf01

Active Member
Hi,

Did it go flat while running or while parked?

If it went flat while parked, then something is drawing too much out of it while the engine is off.

I watched an episode of wheeler dealers or autotrader once where they were getting to the bottom of a constant flat battery, turns out there was a short causing the aircon clutch to activate even with the engine off, causing the battery to go flat very quickly.

You might be able to hear where the power is going to by connecting the battery and listening for the clicks or feeling for heat. Nothing should be getting warm with the engine off, if it is then youre getting to the bottom of the problem. Its not necessarily the hot part thats the problem (in the case of the TV show, it was a stuck relay, a £7 part, and they heard both the aircon clutch click and the relay in the fusebox click), but if this is the case it will point you in the right direction.

Course, you are going to need power to try that. Your batteries will be OK if theres a short, just flat. Might be worth investing in a battery charger.

Jas.
 

Nimby

Distinguished Member
Hi Jas

Thanks for those useful suggestions. :)

The battery seems to go flat if I don't drive the car for at least three days. I have been trying to avoid using the car just for shopping trips and go on my bike instead. The obvious thing is to run the car every day but that seems wasteful.

I have several battery chargers but they all seem to have stopped working. Perhaps the fuses are blown but that's another matter.

I have discovered that part exchange does exist over here (Denmark) which will help make a reconditioned alternator far more affordable.

I'm off to try the starter/charger device after it being on charge for 12 hours overnight. I'm torn between connecting to the battery without the positive battery clamp connected. Or just giving it a try to see if it will start. If there is a short through the alternator diodes it may just undo my overnight charging. :suicide:

I'll be back! ;)
 

Nimby

Distinguished Member
Well the charger/starter didn't work. It hasn't been charged regularly so I can hardly blame it for not working. :blush:

I managed to get a charger going and have connected it to the bare battery. At 3A it may take some time. :suicide:
 

Nimby

Distinguished Member
Four hours of charging got the motor running. I found a friendly mechanic who put his meter on the alternator under maximum load.

His best guess is the radio is drawing power even when everything is switched off. He suggested I should try disconnecting it completely to eliminate it.

Until I figure out how to remove a car radio I'm removing the positive battery clamp while the car stands idle. It takes but a moment to refit it. Which is better than hours of charging before I can drive it. I don't think there's anything which will get lost or damaged without power on an old car like this.

I am most grateful for all your helpful suggestions. Thanks. :smashin:
 

DVD-Man

Distinguished Member
You can test the alternator yourself, get the car running then test the battery again, your looking for 14.4v or there abouts.

A 96 Corolla shouldn't have a ton of gadgets so you might be able to spot aftermarket accessories or perhaps where devices have been removed but show signs of bad wiring.
 

Nimby

Distinguished Member
You can test the alternator yourself, get the car running then test the battery again, your looking for 14.4v or there abouts.

A 96 Corolla shouldn't have a ton of gadgets so you might be able to spot aftermarket accessories or perhaps where devices have been removed but show signs of bad wiring.

Hi

I got the radio out using a couple of hacksaw blades to lift the security springs and pulled off the plugs.

Overnight the battery dropped from 12.7 to 12.6V. (both battery clamps still connected)

It's a Sony Xplod 4 x 50W CDX2050. It all looks standard as do the speakers. (fronts only) All neatly done. No taped up, twisted joints. Nothing else added that I can see.

The car was a one owner from new, non smoker. Very tidy throughout. Spoilt only by the dealer's addition of chemical perfume and a coarse rebuff of the paintwork. :rolleyes:
 

jasonf01

Active Member
If you have a tester that measures amps, you could put it inline with the battery to see what the power drain is with the car off, reconnect/disconnect the stereo should show up if its running the battery down so quickly.

Cars shouldnt take more than a couple of amps when the engine isnt running, if your stereo is causing a problem then this test should tell you for sure.

Jas.
 

Nimby

Distinguished Member
If you have a tester that measures amps, you could put it inline with the battery to see what the power drain is with the car off, reconnect/disconnect the stereo should show up if its running the battery down so quickly.

Cars shouldnt take more than a couple of amps when the engine isnt running, if your stereo is causing a problem then this test should tell you for sure.

Jas.

Thanks, Jas.

Whoops. I should have tried yesterday before I disconnected the radio. I can check now without the radio to see if there is any residual drain. There should only be the clock unless the original Toyota anti-theft system draws power? It's not central locking. Just a big ignition key.

Edit: It's drawing 0.4A without the radio.
 
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car-man

Well-known Member
To check if the alternator is drawing current simply disconnect the alternator wires and measure without the alternator.
 

Nimby

Distinguished Member
To check if the alternator is drawing current simply disconnect the alternator wires and measure without the alternator.

Thanks, but I can't remove the plug from the alternator. Its stuck tighter than I am willing to risk damage trying to get it out. I presume it's a straight pull multi-pin?
 

jasonf01

Active Member
0.4A is fine. Whatever youve changed seems to have fixed it.

Your battery should have a rating on it eg 100AH or amp hours. If yours is 100 AH, it will take that 0.4A 250 hours to flatten it. From what youve said its happening practically overnight with the stereo in, so if its 0.4A with the stereo out Id say you probably have the culprit.

Did the stereo keep the radio stations? I ask because theres two power inputs, one connected direct to the battery for storing the settings which is a low power drain thing (say 0.05A), and another connected through the ignition switch for powering the unit which is a high power connection. Ive noticed some cars wiring (or car stereo wiring) swap over the two power inputs, meaning the stereo is fully powered (and draining the battery) at all times. The other side effect is that many stereos would lose their radio presets when the power went off.

If thats the case, its just a matter of swapping over the two power wires.

If not, probably time for a new stereo.

Jas.
 

Nimby

Distinguished Member
Hi Jas

Hmm. There were some stored channels. Now I wish I'd checked the amperage with the radio connected. I had to remove some trim on the dash but it only amounted to 6 screws and bit of fiddling with some plastic mouldings.

I could be looking at an intermittent alternator fault and blaming the radio. I really ought to reconnect the unit just to double check.

Thanks for all the feedback, chaps. :smashin:
 

car-man

Well-known Member
Thanks, but I can't remove the plug from the alternator. Its stuck tighter than I am willing to risk damage trying to get it out. I presume it's a straight pull multi-pin?


There should be a bolt on connector as well, this is what needs to be removed.
 

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