12v Auxiliary Battery rapid discharge

[OrkneyTim]

Hello,

I went to start the car after a gap of three days. The vehicle was dead - no dashboard display, courtesy lights, nothing. I took off the 12v auxiliary battery and put a multimeter on it which gave a reading of just over 2v.

Assuming the 12v battery was faulty I connected up a brand new 12v and several things occurred.

EV Service Required Stop Safely message on dashboard display, which went blank very shortly afterwards.

The car alarm went off, albeit very faintly.

I disconnected the battery, and the multimeter showed 9v.

So as soon as the 12v battery was connected the car starting draining it down very quickly, to 9v in about 5 minutes.

Any suggestions as to what might be causing this?

When the fault originally occurred nothing had been left on ( headlights etc and the doors and hatch were all closed ). The fact that the battery drain started immediately I connected up the 12v suggests it is not the the usual left something on reason.

thanks in advance for any advice.

 

[kenny256]

This is quite an unusual problem. What model year is your car, and what is the age of the 12V battery that was replaced?

Did you measure the "brand new" battery voltage, or give it a charge to full? Many new batteries sit on the shelves for extended periods and tend to self discharge, such that they really need to be charged before put into service.

If you have a 12V battery charger then put it on the new one and give it a good full charge, then measure the voltage before and after making the terminal connections.

The chances are really good that the errors will clear on their own if the 12V battery voltage was the source of the codes. If indeed there is a large current draw then more diagnostics will be required, such as monitoring the current and pulling fuses to find the suspect circuit.

 

[OrkneyTim]

Hi Kenny.

Many thanks for the reply.

The car is a 2016 model.

The battery that went down was new in January this year after the manufacturers original battery failed.

The brand new battery I put on the other day had a start voltage of 13.6v. I did check it before I connected it up.

As I mentioned originally , in less than 20 minutes the car had drained it down to 9v. I've had the same battery on charge and back up to 13.6 +/- a tiny amount. I did consider connecting the multimeter in series and pulling fuses but at the rate of drainage I wonder if I'd run out of charge before finding the right fuse. But all the usual suspects such as courtesy lights and alarms are irrelevant ( I don't lock the car when it's parked up at home ), so I'm assuming something more nasty at work.

It will be a case of calling out recovery tomorrow and getting a fault reader on the car but I'll replicate the fault for the benefit of the recovery company as I've got two fully charged Aux batteries to play with.

Always frustrating that things only breakdown with the petrol at 90% and traction battery at 80%.

 

[AndyInOz]

One thing that many of us have been caught by is the timer controls for electric pre-heating.

If your car has the MMCS or can respond to the application, check to make sure that there are no timer slots for heating set up.

Otherwise, check anything that is after market.

I have a separate battery installed for my cameras for example, because they would flatten the tiny 12V battery very quickly.

The burglar alarm is also a good thing to check. If it is really turned off, it should only have a miniscule current draw.

You're looking for something that is drawing power from the circuit that remains hot all the time, i.e. is not controlled by the state of the car.

Worst case, you have a wire rubbed through somewhere and you're connecting power directly to ground.

Again, I'd start by inspecting the entire wiring path of everything that has been added after market.
If the vehicle shows any signs of damage anywhere, look closely at any wiring in the vicinity of the damage.

A good example of the kind of thing that can go wrong:

A person had an after-market head unit installed, and the new unit didn't need all the wires in the existing harness, so the installer just left some cables hanging free. The hot wire that is part of the circuit that lights all the lights on the dashboard was shorting to ground periodically, resulting in a blown fuse and lots of odd electrical errors.

While you're doing your testing, test that everything in the car works (headlights, interior light, windows, locks, radio, heater, fan, etc.) if you can find something that isn't functioning properly, that could be a guide to where the problem lies.

For an issue like this, you need a friendly auto electronics specialist who has access to all the manufacturer's wiring diagrams etc.

And specialised testing equipment. (Wire probes, multimeter, oscilloscope, current detector).

Good luck, and please let us know how you go.

 

[DaveL59]

Not sure I'd recommend trying a multimeter to test for the drain, at least not in line with the battery. At that rate of drop I expect there's a fair few amps being drawn so blown fuses in the meter is a high probability. Perhaps worth checking what continuity/resistance there is between the 12v aux positive and negative/body to see if there's some form of short between the battery and fuseboards.

Any non-standard extras, tow bar etc are worth checking over and perhaps disconnecting as a start point. Then work along the high drain circuits, check the inside of the ciggy/aux sockets in case something got in there to short etc. Then its down to pulling all the fuses and checking for shorts with a meter, then adding one back at a time to see where the fauly might be.

I'm also wondering if the infotainment system might be involved, has the potential to shunt a few amps after all.

Beyond that, all cable flex joints (doors, boot lid) for damage, electric windows/sunroof - working, parking correctly etc?

 

[kenny256]

Yeah check for rodent damage, might be a short to chassis to drop from 13.6 down to 9 so quickly.

 

[AndyInOz]

I'm frustrated that manufacturers appear to use wiring with insulation made of peanut butter to attract rats.

(This give me a random idea, maybe I should use electrical cable to bait rat traps!)

 

[kpetrov]

Firstly you check how much amps are draining from the battery, then one by one on every fuse.

 

[kenny256]

Tim,
Remove the terminals from the 12V battery and measure the resistance between the + and - cables to see if a short to chassis exists.

Never seen or heard of one failing, but there is a big diode module to rectify the H-bridge output in the DC/DC Converter. This could create a high current short if one or both legs failed/melted.

 

[OrkneyTim]

Thanks all for the replies.

I can eliminate aftermarket fittings as there aren't any on the car, except for a tow bar.

The vehicle is never locked at home so I'm rejecting and issues with the security system.

What is really annoying is that I popped a fully chargeed battery on the car last Sunday to try and replicate the fault before calling out recovery yesterday and to my horror the car powered up perfectly!

I did a 12v check yesterday afternnon and the battery was sitting on 12v.

I'll do a chdeck later to day and tomorrow.

I think the only way I'll get to resolved is a trip to a garage with diagnostic equipment and skills and see what that throws up.


Rest assured I will update on the findings.

Regards,

Tim

 

[DaveL59]

Does yours not lock automatically when left a while then?

 

[AndyInOz]

I'm wondering if there is a different power draw when the car is left unlocked or locked.

It would be interesting to know.

Leaving the car unlocked and idle for long periods may be a use case that the designers did not allow for.

For example, it is possible that the traction battery is not recharging the 12V battery because the car is unlocked.

 

[OrkneyTim]

Re locked / unlocked.

The vehicle doesn't automatically lock itself if left on its own for a period.

I take the point re the main traction battery not charging the 12v if unlocked.

Yesterday ( 7/12 ) I tested the 12v connected up on the car and the multimeter reading was 12v and this was with the battery on the vehicle for 3 days. Vehicle powered up perfectly, showing 14.6v on the 12v.

This is where it gets really stupid!! I put the 12v battery clamp on, put the boot floor back in and powered up the vehicle to take it out for a test run. 'EV Service Required' warning on dash display and 12v battery voltage fell straight away to 9v. Not enough to power up the ICE.

So, is the boot floor pressing down on a wire, or caused a wire to chafe somewhere ,causing a short / drain?

I suspect I'm getting close now.

Thanks again for all your comments.

Tim

 

[kenny256]

Yesterday ( 7/12 ) I tested the 12v connected up on the car and the multimeter reading was 12v and this was with the battery on the vehicle for 3 days. Vehicle powered up perfectly, showing 14.6v on the 12v.

This is where it gets really stupid!! I put the 12v battery clamp on, put ...

What is meant by putting the 12V clamp on--What is this clamp device? If it is the hold-down clamp for the battery, then it may be putting force on the battery case to cause an internal shorting of the battery plates or current collector bars.

 

[HarriK]

Re locked / unlocked.

The vehicle doesn't automatically lock itself if left on its own for a period.

I take the point re the main traction battery not charging the 12v if unlocked.

Yesterday ( 7/12 ) I tested the 12v connected up on the car and the multimeter reading was 12v and this was with the battery on the vehicle for 3 days. Vehicle powered up perfectly, showing 14.6v on the 12v.

This is where it gets really stupid!! I put the 12v battery clamp on, put the boot floor back in and powered up the vehicle to take it out for a test run. 'EV Service Required' warning on dash display and 12v battery voltage fell straight away to 9v. Not enough to power up the ICE.

So, is the boot floor pressing down on a wire, or caused a wire to chafe somewhere ,causing a short / drain?

I suspect I'm getting close now.

Thanks again for all your comments.

Tim

Or do you have electric tail gate? I have same problem and not finding reason yet

 

[nrayanov]

12V batteries put on the PHEV are not the best and they fail every 2-3 years. Mine failed earlier this year and I had to change it. Also if it's reading exactly 12V it's probably almost dead, you should replace it immediately.

One of the things that's killing the battery could be the Wi-Fi module, so you start by deactivating it.

 

[HarriK]

Wifi module goes off if car is sitting down more than 35hours. Car charges 12volt battery automaticly 2pm evry day before wifi goes off.

My problem was oem phev radio which drains battery after 2days. Same issue with other phev also here in Finland.

 

[michael8554]

12V batteries put on the PHEV are not the best and they fail every 2-3 years.

Seriously ?

My UK 2014 still has the original 12V battery.

Measured just now, 12.17V at 2 degrees C on the "jump start" terminal in the fuse box under the bonnet.

 

[nrayanov]

You are just lucky, Michael. There are thousands of people who fell victim to their beliefs that the 12V battery can endure for long.

You can check the PHEV UK group on Facebook.

 

[michael8554]

Agreed, just look at all the recently posted 12V Battery Problems.