Short circuit in car

[DIYerPhil]

I have a Citroen C4 that is suddenly out of power completely (just like having a dead battery). The battery is checked to be still good and there is no blown fuse.

I did some tests with my multimeter and found that there was continuity between the positive terminal and negative terminal of the battery, meaning that there is at least one short circuit somewhere in the system.

I tried pulling out fuses one by one trying to break the continuity, but was in vain until I disconnect a battery fuse (125Amps) which can be traced to a connector in the fuse box (see photo).

I tried looking up the user manual but there was no indication of what the connection or the fuse is for. I tried to locate the relevant system by turning on the car with that connector disconnected, but the electrical system by and large is still not functioning.

I have thought about buying a short circuit finder (like ECT300) to trace the location of short circuit, but with the huge bunch of wires associated with the connector, I am not sure whether it would work and not give false alarms here and there.

Have anyone had any experience in dealing with this before? Any thoughts are much appreciated. Thank you in advance.

 

[RandomGrinch]

I did some tests with my multimeter and found that there was continuity between the positive terminal and negative terminal of the battery,

Did you disconnect one of the battery terminals first, or did you attempt to measure continuity/resistance with the battery in place?
If the latter, you would be attempting to measure the (extremely low) internal resistance of the battery - something that may not do your meter much good.

 

[JohnD]

I did some tests with my multimeter and found that there was continuity between the positive terminal and negative terminal of the battery, meaning that there is at least one short circuit somewhere in the system.

It is normal for a circuit to have continuity.

For example, the two wires to a light bulb have continuity through the filament.

It need not be a short circuit.

 

[foxhole]

Possible circuit breaker fault ? See here.

 

[carmanmemoranda]

Have you checked the starter motor before going further ?

 

[DIYerPhil]

Did you disconnect one of the battery terminals first, or did you attempt to measure continuity/resistance with the battery in place?
If the latter, you would be attempting to measure the (extremely low) internal resistance of the battery - something that may not do your meter much good.

Yes, I have the battery disconnected first before measuring the resistance between the two terminals. And the resistance was extremely low (reading was 0.05 on a 200 Ohm setting) until I disconnect the connector in the fuse box.

 

[DIYerPhil]

It is normal for a circuit to have continuity.

For example, the two wires to a light bulb have continuity through the filament.

It need not be a short circuit.

Yes I understand what you mean and sorry for the confusion. To provide more context, the resistance between the two terminals (with battery disconnected) was just 0.05 in a 200 Ohm setting, which seems a bit low. And after disconnecting the connector in the fuse box and putting back the battery in place, some of the electrical aspects such as dash lights come back on again, which previously have none. My theory was that the shorted circuit took all the current, rendering other functions failed. By disconnecting the shorted circuit, the current can now flow to various other parts, therefore some electrical features come back on. So that’s why I think there was a short circuit. I am all ears if there is anything wrong with my analysis.

 

[DIYerPhil]

Possible circuit breaker fault ? See here.

Unfortunately I have checked all the outlets from the battery and they are all getting power, so I guess it’s not the circuit breaker that was at fault. But thanks for the insight.

 

[DIYerPhil]

Have you checked the starter motor before going further ?

There was no power getting anywhere, not even the window or central locking. So I guess the problem should be a wider electrical issue? Sorry for the confusion.

 

[Burnerman]

Expect there to be a small electrical drain at all times - this is to enable the immobiliser, radio memory etc.
This is what I would do.......my multimeter is capable of reading 10 amps DC though.
Disconnect the battery positive terminal, and insert the meter between the battery post and the loose terminal. Any current draw will then be seen.....only a small current loss is acceptable, maybe one amp or so.

After that, investigate the condition of the thick lead going to the starter motor for fraying, tightness or corrosion etc.

If you have your battery fully charged, does it go flat within a couple of hours, once connected to the car?

John

 

[DIYerPhil]

Expect there to be a small electrical drain at all times - this is to enable the immobiliser, radio memory etc.
This is what I would do.......my multimeter is capable of reading 10 amps DC though.
Disconnect the battery positive terminal, and insert the meter between the battery post and the loose terminal. Any current draw will then be seen.....only a small current loss is acceptable, maybe one amp or so.

After that, investigate the condition of the thick lead going to the starter motor for fraying, tightness or corrosion etc.

If you have your battery fully charged, does it go flat within a couple of hours, once connected to the car?

John

John, thanks for the method provided, I have never thought about measuring current.

But in my case, I think the drain of power from the battery is quite obvious. Before the electrical system suddenly broke down last week, I have been constantly running the car through motorway. As there have never been any warning lights regarding my battery, I assumed that the alternator was running ok and the battery was fully charged at all times.

One day, all of a sudden when I tried to start the car, there were a few weak cranks, followed by a completely dead electrical system (not only the car won’t start, but there was even no dash lights and all accessories such as window and central locking were not working). Several days later when I had time to work on the car and measured the voltage of the battery, there was only around 10v remaining, which was well below the normal 12.6v.

My theory was that there had been chronic issue with wiring, and the last time I tried to crank up the engine the wires just gave it completely and shorted itself out. When I disconnected the suspected culprit connector at the fuse box, some dash lights did come back up. So I am inclined to believe that there was a short circuit. I am eager to know what you think. Cheers.

 

[Burnerman]

To be honest Phil, if the short circuit was large there would be one hell of a spark when you reconnected the battery terminal......you'd both see it and hear it.
If you find a significant current drain, disconnect the alternator and see if the drain stops.
I appreciate that French wiring ain't the best but normally it's pretty reliable.
John

 

[DIYerPhil]

To be honest Phil, if the short circuit was large there would be one hell of a spark when you reconnected the battery terminal......you'd both see it and hear it.
If you find a significant current drain, disconnect the alternator and see if the drain stops.
I appreciate that French wiring ain't the best but normally it's pretty reliable.
John

John, I really appreciate your help on this matter.

Can you elaborate more on the reason behind disconnecting the alternator? What does it mean if the drain stops after disconnecting the alternator?

 

[Burnerman]

The alternator, when it is spinning, produces alternating current (AC) which is no use to the car which runs on direct current (DC).
Inside the alternator there is a device called a rectifier that converts AC to DC - this is done by using electronic 'valves' called diodes which allow current to pass in one direction only.
If the diodes fail, then they can allow electricity to flow back into the alternator, which can effectively become an electric motor and this will flatten your battery big time. Therefore, disconnecting the alternator just rules this factor out.
I'm not saying that this is your problem at all, but I have seen this before.
Be lucky!
John

 

[DIYerPhil]

The alternator, when it is spinning, produces alternating current (AC) which is no use to the car which runs on direct current (DC).
Inside the alternator there is a device called a rectifier that converts AC to DC - this is done by using electronic 'valves' called diodes which allow current to pass in one direction only.
If the diodes fail, then they can allow electricity to flow back into the alternator, which can effectively become an electric motor and this will flatten your battery big time. Therefore, disconnecting the alternator just rules this factor out.
I'm not saying that this is your problem at all, but I have seen this before.
Be lucky!
John

John, thank you for your explanation. I really can't thank you enough. Will definitely give it a go and see how it goes!