Battery Drain with a cyclic load?

[Guest Greg Ross]

About a year and a half ago I had a battery drain down problem, turned out to be in the "Driving Lamps" circuit. As long as I left them turned off there was no problem.

Was away from home last week and on our return the Reatta had a dead battery-reading 9.66 V

Recharged it and had it go down in voltage again overnight. Recharged it again, disconnected the battery and no drop in voltage. Appears the Battery is Ok.

As per the '88 FSM section 6D1-6 "Battery Electrical Drain Check" I inserted the VOM in line at the Battery/ negative connection. I pulled the CPS (No. 5) Fuse as the first step.

When I connect the meter I hear a relay closing up in the front left corner of the car, I see about 5 Amp load dropping back to .3 A and then after about 10 seconds it goes to .01 A

With the CPS Fuse plugged back in I see the same Relay response as above, then sometimes immediately and sometimes with a lag of a few seconds I see a cyclic pattern. It goes from .05 A to .10 A to .19 A, down and up, down and up in about a 2 second cycle continuously.

Included on that CPS Fuse circuit is the CPS module, BCM, IPC, GCC, CRT Controller, Radio module, Casette Deck module, and Chime module.

We first thought it might be the Chime Module, it hasn't worked thankfully for quite some time-never did like the noise. Thought perhaps there was a problem with one of the signal feeds, door switch, ignition switch, wiring, causing the Chime module to function (2 seconds would be about the audible sound rate?) Pulled the glove box this morning, pulled the Chime module and the "Beat Goes On" -same cycling load showing at the Meter.

Swapped out the BCM while I was in there, no difference!

According to the FSM section noted above it indicates if the load drops below 50 milliamps with the CPS fuse pulled you should reconnect the negative battery cable and "see BCM Draw Test"

I have been back and forth thru the FSM til I'm half blind and I cannot find any reference to this BCM Draw Test.

Any and all suggestions greatly appreciated.

Not directly related to this issue apparently but one of the other load tests you run into (if the load doesn't dissapear by pulling the CPS use) is to disconnect "Fusible Link F"

I was looking at the cluster of fusible links and could see no immediate means of identifying which was which-anybody?

Greg

[Jim]

I too have tried on a couple of occasions to figure out which fusible link is which with no good results.

I cannot help on the service manual procedures but do know it is normal to hear the click coming from the headlight control module when you reconnect the battery and like you observed there will be a decreasing current drain for about a minute.

[Guest kennyw]

Yah:> a module in the left front lower.......I have the same click, its on.....and the battery drains....sometimes a week. Sometimes just a day.....I am no good at using a meter to see the drain.....car is seldom driven....I just use a battery disconnect.....If you find a fix I sure would like to keep my battery connected..........ken

[Guest Greg Ross]

I could easily get around this problem by installing a toggle switch under the dash that's spliced into Fuse No. 5 feed wire, the CPS circuit. That way I could disable the fuse without pulling it but I would also lose the clock and radio station presets evry time it's switched off.

And my problem may not be the same as yours' Kenny. As Jim points out, the sound we hear when the battery is hooked up is the Headlight module warming up, or whatever. Once it goes thru its' start cycle the load then drops, at least in my case drops down to nothing.

I think I'm right, there's no benifit at this point pulling fuses, they're all separate functions from the CPS, Dash and BCM. There's a relay or module in that CPS circuit somewhere thats' gone wonky. The FSM schematic notes says not to test resistance on any of those modules as they're solid state.

[Guest kennyw]

And my problem may not be the same as yours' Kenny. As Jim points out, the sound we hear when the battery is hooked up is the Headlight module warming up, or whatever. Once it goes thru its' start cycle the load then drops, at least in my case drops down to nothing.

so: the headlight module is supposed to come on.....OR...be on when the battery is connected? Then somehow, its drain on the battery drops to 0? That could be the reason my battery stays up and sometimes is dead. The module isn't droping to 0....? Someone will speak up and tell us how this module stops taking power? I hope........ken

[Guest steakneggs]

Now I know what that click is every time I hook up the battery. I had problems with battery drain for awhile but it fixed itself. Steak

[Guest simplyconnected]

Gentlemen, let's put things in perspective with a little MATH (that everyone hates):

Your battery is about 55-amp/hour (or more). It produces 55 amps for one hour.

With a constant drain of .19amps:

55amps/.19amps=289 hours, (nearly five days to discharge).

If you are discharging in 24 hours, your drain HAS to be 55/24=2.3-amps continuously.

Something is draining a whole lot more than you are measuring, OR your battery is shorting internally. Remember, if one cell goes bad, there goes 16% of your capacity (and 2-volts).

Have your battery checked with a hydrometer.<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Ross</div><div class="ubbcode-body">The FSM schematic notes says not to test resistance on any of those modules as they're solid state.</div></div> That's right, resistance checks mean nothing. you can still check current draw while it is connected.

Sometimes your alternator/voltage regulator pulls power when a diode goes bad. The alternator is always connected to your battery. You can easilly check it by pulling the wires off, then check for current flow at the battery.

Hope this helps. - Dave

[Guest Greg Ross]

I don't have a constant draw of .19 amps as you've used in your example. A failed diode would not draw current in a cyclic fashion as I have described.

Thought my initial decription made clear that I had read load at the battery and the cyclic load was what I discovered.

Sealed/ maintenance free battery so a load test would be necessary.

Thanks anyway

[Guest kennyw]

this is the module that makes the click-on noise on my reatta..The battery cable puts out a nice spark when connecting. From this I figure a large current draw. answers? ken

[Guest Greg Ross]

Ken,

With my Volt Meter set to Amps (maximum 10 Amps) And the ground cable disconnected from the battery I touch the battery neg. anode with one pin and touch the other to the Neg. cable end. As soon as I make this connection I see 5-6 Amps on the Meter, as mentioned previously it soon drops back to about 1/3 of an Amp and then (Jim says within one minute) within about 10-15 seconds on my car the amperage drops right off. Whatever this module does to warm itself up or whatever, that's what it does. I think like me, you have something else that's draining slowly to ground/ seized relay/ something that's running the battery down.

It's a fairly basic digital Meter BTW, DC and AC Volts, Ohms and the one setting for Amps-probably not more then about $30.00

Same as you, when I connect the battery cable I see some arcing while I'm tightening up the side terminal. That sparking is according to my metering only 5 amps!

[Guest Greg Ross]

Had my wifes' car in for a major service interval and brought the FSM along for some light reading while I was waiting.

Went thru schematic by schematic and plucked off/ listed the relays and fuses by system with the intent of tackling the next phase of troubleshooting in a logical fashion.

Went out this morning and rigged up the VOM, positioned it on top of the strut tower so I could see it from the passenger side as I pulled out relays, etc. I connected and disconnected several times. All I read was 20 and 30 miliamps, steady.

It had seemingly healed itself, I hate intermittants!

[padgett]

Sometimes the act of measuring influences the outcome. The right size hammer often helps.