Dead Battery electrical question (Locating parasitic draw)

[DarkStar]

So last week I replaced the 45 month old battery. AGM style. I removed it and tried to charge it on my tender but it kept failing.

Put the new battery in and a week later car is dead. Just pulled it out and placed on a charger. I fear there is a drain someplace, possibly the vacuum pump system for the locks.

Does anyone know if the pump will continue to run if the vacuum system has a leak?

I ask because the door locks did not actuate when I unlocked it before trying to start it.

 

[jaymanek]

The pump will continue to run if there is a leak but only for a few seconds.

It may keep actuating if there is a fault somewhere.

You will need to carry out a battery drain test by connecting an ammeter in series between earth case and battery terminal. Then you can track down the drain by pulling fuses until the drain drops.

 

[JC220]

This might also make good reading-


http://www.500eboard.com/forums/showthread.php?t=10073

See if your symptoms match what is described there. (Fuel Pump priming when battery hooked on etc)


And as said above you need to carry out a Parasitic Drain Test to find out what is causing the draw. Also make sure the car has a full set of new Copper Fuses; when electrical gremlins in W124’s begin that’s a good thing to do first.

 

[DarkStar]

So no drain seen by system when the trunk pin is pushed in. ~.5A if the trunk light is on.

I charged the new battery off the car for a day or two, it completed the charging cycle and the charger showed green.
I reinstalled it in the car but it would not even give me enough juice to start.

I jumped it and drove it a while. Checked voltage, was 11.5V, checked it with car running 13.65V, so alternator seems to be working. After driving, with engine off voltage was 12.55V. Checked for any current draw and again saw zero.

It started this morning, drove for a while and will check again tomorrow. Might be just a bad battery out of the box.

 

[lowman]

The pump will continue to run if there is a leak but only for a few seconds.

It may keep actuating if there is a fault somewhere.

You will need to carry out a battery drain test by connecting an ammeter in series between earth case and battery terminal. Then you can track down the drain by pulling fuses until the drain drops.

its is alot better measuring voltage draw over the fuse..pulling fuses disturb the whole system..waking it up every time you pull and conenct a fuse.
So its much better measuring "voltage" over the fuse...meaning..on both sides of the fues..there should be 0 volts..if there is ANY voltage between the "fuse ends." you have a parasitic draw

 

[DarkStar]

Thanks lowman! I checked the battery today it was down to 8V ! Checked the current drain and it was 2A! I need to run thru the system and figure out where this is happening.

I don't understand how there was now current draw a day ago, but now there is.

No vacuum to operate the door locks either.
I have to believe there is a correlation. I'll try to charge the system and run thru all the fuses.

 

[JC220]

It's sounding very much like the diagnostic socket to me. To test that theory is quite simple

Remove the smaller cable which is attached to the battery + cable by a 10mm nut. This is the power feed to the Module Box. Leave the car for a couple of days with a fully charged battery & see does the battery stay up.

Im not sure what Lowman means by Voltage. Current draw is measured in Amps - not volts. You could do it fuse by fuse yes. But is is more intuitive to monitor the amp draw for the whole vehicle at the battery negative terminal. Then pull a fuse by fuse.

Top tip - using a multimeter In this manner will blow it quite readily. Use a 'shunt wire' on initial hookup to protect your multimeter. A trick I also did was fix the multimeter wires in place & leave it connected over night etc but switched off. Then the next day or at random times turn it on & check the amp draw. This way you can catch stuff that comes on much later or is problematic.

A healthy w124 will read 0.04 - 0.05 Amp draw.

 

[lowman]

you could have a bad battery indeed.
But do the parasitic draw test like i mentioned...measure OVER the fuse..and see what fuse has a draw...easy peasy.When you measure this way..you DONT want to see ANY but 0 volts over the fuse.is there ANY more than 0 volts..then you have a draw on that circuit.

If the draw is variable..something is obviously shutting on and off..and not many things DOES that..appart from maybe the central locking ...of course you can never know..but...start doing the parasitic draw over the fuses...and go from there.thats my tip

 

[gsxr]

Simple test for a drain at the diagnostic socket.

Connect meter, observe ±2A draw / current drain. Now remove GM/BM module from CAN box. See if current draw goes away. If so... your diagnostic socket X11/4 is highly suspect. BT, DT, same as JC220... click here for more details on diagnosing/repairing X11/4.

 

[DarkStar]

I thought I might isolate things by removing the small cable from the battery, but wasn't sure where it went or what it was, thanks for the info on the socket. It is acting like it is waking up a while after being disconnected from the battery. At first it is flowing zero, but then later as much as 3.5A.

Is the vacuum system for locking also dependent on electronics, it seems like it does not work at all with battery disconnected. That or the vacuum leak is massive and it won't hold any vacuum.

With the fuse box up front I can't monitor the battery/Ammeter and pull fuses. Which means I will likely have to enlist a helper.

Not sure how to test drop across our fuses, the bottom of which is buried, I guess it can be done across the fuse wire that is exposed.

As for the socket, is there a known issue with it that can be fixed or is it a CAN module that is bad?

Thanks for all the advice!

 

[Jlaa]

With the fuse box up front I can't monitor the battery/Ammeter and pull fuses. Which means I will likely have to enlist a helper.
Thanks for all the advice!

one technique that might work for you is to set your phone in video record mode, placed in the trunk, aimed at the ammeter. Then, while you are at the front pulling fuses, yell out "FIRST FUSE!" Pull, replace, yell out "SECOND FUSE!" Pull, replace, etc. Then review the video.

 

[lowman]

I thought I might isolate things by removing the small cable from the battery, but wasn't sure where it went or what it was, thanks for the info on the socket. It is acting like it is waking up a while after being disconnected from the battery. At first it is flowing zero, but then later as much as 3.5A.

Is the vacuum system for locking also dependent on electronics, it seems like it does not work at all with battery disconnected. That or the vacuum leak is massive and it won't hold any vacuum.

With the fuse box up front I can't monitor the battery/Ammeter and pull fuses. Which means I will likely have to enlist a helper.

Not sure how to test drop across our fuses, the bottom of which is buried, I guess it can be done across the fuse wire that is exposed.

As for the socket, is there a known issue with it that can be fixed or is it a CAN module that is bad?

Thanks for all the advice!

you have to measure in the fusebox..OVER the fuse..from the top of the fuse...to the bottom..you are bascally measuring the power going THROUGH the fuse...and when measured in series..there should be NO voltage on it..
So if there is ANY voltage there....then you have parasitic draw.You should NOT do the parasitic draw test by putting the DVOM in series with the battery...then when you pull fuses..you disturb the system..and you CAN get faulty readings.Im not saying you DO get faulty readings...but the way i described is bullet proof when it comes to NOT deal with systems beeing woke up by pulling and putting in fuses.

The small cable going from the battery is the power feed to the CAN network..and should not be of any issue.If there is any issues with it..it will be purely a connection related one...either at the battery connection..OR the connection plate just on the side of the CAN box.A plastic plate with 4 wires i think...screwed onto it..

 

[gsxr]

I thought I might isolate things by removing the small cable from the battery, but wasn't sure where it went or what it was, thanks for the info on the socket. It is acting like it is waking up a while after being disconnected from the battery. At first it is flowing zero, but then later as much as 3.5A.

Is the vacuum system for locking also dependent on electronics, it seems like it does not work at all with battery disconnected. That or the vacuum leak is massive and it won't hold any vacuum.

With the fuse box up front I can't monitor the battery/Ammeter and pull fuses. Which means I will likely have to enlist a helper.

Not sure how to test drop across our fuses, the bottom of which is buried, I guess it can be done across the fuse wire that is exposed.

As for the socket, is there a known issue with it that can be fixed or is it a CAN module that is bad?

Did you try the test I outlined in post #9 above? Do you still get up to 3.5 amp draw with the BM/GM module pulled out of the CAN box?

 

[DarkStar]

Have not tried it Dave. Just got back from getting an alignment done on the F150...

 

[JC220]

The small wire at the battery terminal goes to the Modules. The real issue is the diagnostic socket has permanent power inside it. If the socket is faulty this power feed will cause CAN errors & wake up the ECUs very randomly. This this is how that power lead can drain the battery. The Modules themselves will consume the power.

I can tell you this happens maybe right away- maybe 8 hours later- very hard to nail down. Either disconnecting that cable or pulling the base Module will eliminate it. So with your 2 amp draw showing up- remove the lead or pull the base Module. If they are consuming the power the drain will vanish. The Modules can consume between 1.5 - 2 amps.

 

[DarkStar]

Just ran out and tried it. Disconnected wires for aftermarket alarm and the CAN. Still had a
3.11A draw.
Will attempt testing fuses. Read a good article on testing for voltage drop across fuses. Check for small mV drops
(eg 3mV ) depending on fuse rating.

 

[MCR01]

Checking the current flow is a whole lot easier with a "clamp meter". The better ones will do AC and DC and will read down to 5mA; many will also go to ~80Amps; so useful around both the workshop and house. Using a clamp meter means you don't have to disturb any wiring, you just have to have access to the wire.

 

[gsxr]

The small wire at the battery terminal goes to the Modules. The real issue is the diagnostic socket has permanent power inside it. If the socket is faulty this power feed will cause CAN errors & wake up the ECUs very randomly. This this is how that power lead can drain the battery. The Modules themselves will consume the power.

I can tell you this happens maybe right away- maybe 8 hours later- very hard to nail down. Either disconnecting that cable or pulling the base Module will eliminate it. So with your 2 amp draw showing up- remove the lead or pull the base Module. If they are consuming the power the drain will vanish. The Modules can consume between 1.5 - 2 amps.

Correct! Either pulling the small (~8 gauge) wire off the positive battery terminal, or removing the GM/BM, will effectively do the same thing. Power for the other modules routes through the GM/BM which is why both test methods are effective to eliminate the diagnostic socket. I posted a mind-numbingly detailed explanation in the X11/4 thread linked previously.

Just ran out and tried it. Disconnected wires for aftermarket alarm and the CAN. Still had a 3.11A draw.

OK, if the CAN wire was removed and you still had the draw, it's probably not the diagnostic socket. I'd still pull the BM for grins but it sounds like something else is the root cause. Have you disconnected the cell phone module on the left side of the trunk, if present? I've had problems with those causing a parasitic draw.

 

[lowman]

Just ran out and tried it. Disconnected wires for aftermarket alarm and the CAN. Still had a
3.11A draw.
Will attempt testing fuses. Read a good article on testing for voltage drop across fuses. Check for small mV drops
(eg 3mV ) depending on fuse rating.

yes...
go ahead..been suggesting this now for the last 3 posts...this IS the way to do it..not pulling any modules or stuff..measure OVER the fuses..to get a clue to WHERE the parasitic draw is.

greeets

 

[DarkStar]

I have a clamp type meter on my wish list.

A good auto probe tool is also on my list as well.

 

[DarkStar]

Curious if anyone knows if the 150 A unit can be rebuilt or at least replace the diodes?

I think I have a failed diode.

In testing the system for parasitic draw I found AC voltage at battery.
I'm still seeing up to a 4A draw on the system. No mV drop across any fuses.

I upgraded to a larger Alternator a long time ago, not many miles on it so it's worth saving if I can.

 

[DarkStar]

First couple places I looked, the regulator wasn't sold, but I did confirm that peach has it for $35

 

[DarkStar]

New regulator and everything is good.

PITA to remove the larger alternator. Swapped the regulator while it was still in the car, could not get the thing out! It's been a long time since I installed it, have no idea how I got it in there without removing the swaybar...

 

[lowman]

awesome