Battery light on and cannot start the car

[N-Gen]

It's a 90' (as it turns out) 316i with the 1.6 M40. I gave it a few spins when I got it last week, day 1 I thought the battery was weak as when I turned the key I could hear clicking sounds but the engine wouldn't start.

Took the battery in, charged it and the next morning it started without a problem. A couple of starts later, everything was still fine. Then at one point I tried to start it, none of the other instrument lights came on (parking brake light and so on) apart from the battery light. I changed to a better newer battery that was charged to no avail. When I turn the key to start it's dead silent, no clicks or any sort of sign of life. We thought it might be the starter but surely you could hear it click or attempt to kick off when the key is turned.

I'm lost at this point, any ideas?

[ELVA164]

How long after you got the new battery did it die? It sounds like you have a short somewhere that's draining the battery. Start by giving the battery a charge to make sure it has some juice. Use a test light at the battery to check for shorts. Disconnect one lead to the battery, attach the clip from the test light to that cable, and touch the probe to that post. If the light lights up, you have a short. Start pulling fuses one at a time until the light goes out. Check anything attached to that circuit for shorts.

[N-Gen]

The newer battery didn't even get the car started once, dead silent before and after the change. I checked both batteries with a multimeter and they were both fine, in fact all the electrics operated just fine and the older battery is now powering LED strips in the garage and happily getting trickle charged off of a solar panel.

I will however conduct the tester test for shorts once I visit the old girl, probably on Saturday.

[997_rich]

you should do the test for shorts for sure.


BUT... i notice that you use the words "old" and "newer" battery. Don't assume those are good batteries. You can have them checked at the store or you can check them in the car and be reasonably certain in your results.

Pick your best battery, charge it, measure it out of the car (should be about 12.5v).

put it in the car, connect the wires, no key in the ignition, measure the voltage across the terminals (again, should be about 12.5, if you're getting like 8v then it's prob a short in the car, sort that out until you can get 12.5v).

now if you feel good about no shorts, get a helper, measure the voltage at the battery while the helper turns the key (should be about 12v while the key is turned). if it's like 8v or less and keeps going down while the key is turned you need a new battery.

while you're playing this game, once you get the car started measure the voltage at the battery again. should be around 14v. if it's like 12v you probably need a new alternator.

[N-Gen]

Measured them both at around 12.45, 12.47-ish volts outside of the car, will run some tests with it in the car then. Hopefully it's a short and not the case for a new alternator.

[N-Gen]

Just popped round real quick, tried both batteries which are sat below 12v (11.8v and 10.9v) at the moment, figured I'd try anyway while was there. Turning the key draws no power whatsoever it seems. Brought the newer one which was at 11.8v with me home for a good couple of days charge and will try again.

[roguetoaster]

Is this a trunk mounted battery? If so you might want to check the fusible link.

The likely alternative is the ground either at the passenger side engine mount or at the alternator is shorting on something, or is simply no longer connected.

[N-Gen]

It's a front mounted battery, drivers' side on RHD.

[ELVA164]

Another thing you could do that makes it pretty clear whether or not the batteries are good is buy/borrow a load tester and just load test the batteries.

[N-Gen]

In that case I think I could just try starting another car with it, right? It's on charge right now, will see on Saturday.

[bmwman91]

Does the battery light stay on even when the car is off / key is removed?

If so, the rectifier diodes in the alternator are shot and you will need a new or rebuilt alternator.

[N-Gen]

No, it's only on when they key is turned and the usual dash instrument lights come on. However they don't light up anymore, just the battery. When the key is not in that position the battery indicator light is off.

[N-Gen]

Ok, it's update time.

Put a fully charged battery in, nothing happened, battery light was still on when the key was turned. Primed the starter and the starter turned with no problem. It seems like somewhere there might be something disconnected as there is simply no current going into the starter motor.

I did find disconnected cables in the car and under the hood but I have no idea if those should actually be related.

The first photo shows the disconnected cables under the dash, the second one shows a disconnected plug with cables going into the engine and the air filter.

[jlevie]

With a fully charged battery in the car (one that reads 12.7v) if the starter fails to turn the engine there is a problem with the primary power/ground connections, a problem with the starter solenoid control power, or a bad starter. Diagnostics would be:

Use a meter or test light to check for solenoid control power when the key is turned to start.

Use meter to see that primary power is present at the starter when the key is turned to start.

Use a meter to measure resistance from the starter case to the battery ground.

If those checks don't reveal a problem the starter is bad.

[N-Gen]

Sorted the starter problem, bypassed the ignition cable that goes into a relay, directly to the starter and the engine turned. It did not start but that's probably because I removed the alarm and the immobiliser kicked in.