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Old 10-22-2015   #1
90 L98 TransAm
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Battery Drain

I’m trying to track down an excessive drain on my battery. my alternator is a recent rebuild and the factory gauge indicated it was charging the battery at 13.5 – 14 volts. battery voltage after a drive was 12.7 volts. I started tracking the voltage drop. after sitting for two days the voltage was down to 12.3 volts. I charged the battery back up and let the car sit for five days at which time the voltage was down to 10.2 volts.

I took the 17 month-old battery back to Wal-Mart for testing. I had asked them if it needed to be charged up for testing and they said “no”. so I laughed a little when they tested it and all they could tell me was it ”needed a charge”. they decided to give me a warranty replacement battery.

So I put a multimeter in series with the ground cable and negative battery terminal and measured 140 mA. Supposedly a drain over 50 mA could be considered excessive. my friends IROC has a drain of just 9.7 mA.

I did the following to try to isolate the drain:
Disconnected both leads to the alternator – no change in current drain.

Removed ALL of the fuses in the interior fuse box – no change. Also disconnected a couple of power taps to the fuse box for boost gauge, gauge sensor, MSD box, etc. with no change.

Disconnected the power wire from battery to subwoofer amplifier and removed Pioneer head unit from the car. Drain dropped to 130 mA when I removed the head unit.

I did notice that when I kept the meter in place for ~3 seconds relays at the firewall and very front of the car would click and the reading would go to 0. not sure if that was some sort of meter protection function or what.

The Owner’s Manual indicates there are two 15 A fuses in the “convenience center” which I believe is under the instrument panel near the steering column. I haven’t located this yet but would like to know what these fuses protect (headlight system?).

The GM Service Manual indicates there are three headlamp relays at the front of the car (headlamp motor, headlamp isolation and headlamp motor isolation) but I have not been able to find any of them. do you have to do disassembly to reach these relays?

Is the ECM a likely source of the current drain?

Any suggestions on what else to check would be much appreciated!
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Old 10-22-2015   #2
rhomanski
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GTA Year: 1988
GTA Engine: 350 TPI Automatic
Re: Battery Drain

The motor for the rear hatch, power door lock switches, computer. That's all I can think of you haven't mentioned. The rest would require the key to be on. I think.
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Old 10-22-2015   #3
90 L98 TransAm
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Re: Battery Drain

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Originally Posted by rhomanski View Post
The motor for the rear hatch, power door lock switches, computer. That's all I can think of you haven't mentioned. The rest would require the key to be on. I think.
thanks rhomanski - are the items you mentioned protected by the fuses in the fuse box (and would have eliminated/reduced the current drain when I pulled their fuses) or are they on their own separate circuits?
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Old 10-22-2015   #4
rhomanski
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GTA Year: 1988
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Re: Battery Drain

I'd have to look it up. I'm pretty positive the computer is on a fuse under the hood hidden in the wiring harness. I think the others are fused elsewhere too but I'm not sure. I'll look into it in a while.
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Old 10-26-2015   #5
90 L98 TransAm
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Re: Battery Drain

OK. I think I made some progress today. Removed the fuel pump
20A fuse (at least I think that's what this fuse is for) since it appears to have a direct connection to the battery's positive terminal:



No change in current drain so that wasn't it.


Then I went searching for the "Convenience Center" under the instrument panel. for access you only have to remove the lower kick panel under the steering column not the knee bolster above it. look for a black plastic box that looks like this and pull it out sideways:





That is the door open chime.


Look straight up and you can see the convenience center shown on the right side of this picture with two blue 15A fuses and the white cube.





I pulled the lower 15A fuse here then checked current drain and found that it had dropped from 130 mA to ~3.7 mA (the stereo head unit is still out of the car). the headlights light up but do not raise with this fuse removed (they work fine with it installed). so I think I have found the circuit that is causing the excessive current drain.

I still need to locate and check the three headlamp relays, associated wiring and headlamp motors at the front of the car. Does anyone know where those relays are located? Do you have to remove the front bumper cover or some other parts to access them?
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Old 10-31-2015   #6
90 L98 TransAm
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Re: Battery Drain

I re-installed the convenience center fuses and removed the headlight door module from the firewall near the brake booster. I know that a module that doesn't shut down can cause a current drain. I checked the current drain and it was 3.7 mA. my factory original module for a '90 TA is GM #16509097 per the little orange sticker on the firewall side of the module:




Performed the headlight door module tests in the Pontiac Firebird Service Manual. 4-pin connector C2 is on the passenger side of the module and 5-pin connector C1 is on the driver side. all testing yielded the correct results. the manual indicates that if the wiring between the module and the headlight door motors is also OK I should replace the module.





so I bought a used module #16514174 from a '91 Firebird. this site indicates it is the replacement for my module:

http://www.gmpartswiki.com/gmpart?gmpartno=16514174





you just disconnect the two connectors, slide the old module out toward the driver side and slide the new one in. my headlights still work as they should. current drain dropped to 0 (on 10A scale) and there was no voltage drop over night.

I read that the solder joints inside the headlight door module can break so I will be opening up my original module and looking for any obvious breaks or cracks in soldered joints. then try fixing it myself or take it to someone who solders everyday.

here are some links that might be helpful for others having battery drain or headlight door issues:

http://www.aa1car.com/library/battery_runs_down.htm

http://www.thirdgen.org/forums/dfi-e...line-fuse.html

http://www.thirdgen.org/forums/elect...ery-drain.html

http://www.thirdgen.org/forums/elect...-location.html

http://www.thirdgen.org/forums/elect...odule-fix.html

http://www.firebirdnation.com/forums...-third-gen-ta/

http://www.thirdgen.org/forums/elect...ol-module.html
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Old 10-31-2015   #7
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Re: Battery Drain

Nice detective work! I look forward to seeing what you find inside that module, because as you indicate, the usual failure mode for these is intermittent/no operation, not current drain.
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Old 10-31-2015   #8
90 L98 TransAm
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Re: Battery Drain

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Originally Posted by DynoDave View Post
Nice detective work! I look forward to seeing what you find inside that module, because as you indicate, the usual failure mode for these is intermittent/no operation, not current drain.
thanks. yes it is strange because my headlights always worked just fine. but I don't want to worry about my battery going dead in just two or three days.

you can pry the module case open with a small screwdriver:





bottom of circuit board:




the board drops right out of the front of the case:






unfortunately, I didn't find any obvious broken solders or fried components after a quick check with a magnifying glass. maybe a good electronics tech could find and repair the problem.


here's a link where someone opened up their module. you can see that the module design appears to be somewhat different than mine:

http://forums.aaca.org/topic/222906-...e-information/
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Old 11-01-2015   #9
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Re: Battery Drain

Yes, working or not, you wouldn't want to live with this drain.

Actually, as I was reading this thread, when you got to the chime module, I expected to hear it was culprit. Not that they are know for this necessarily, but I've had two GM vehicles with this style module, and both had this module removed by a previous owner. I guess they were fairly troublesome.
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Old 11-01-2015   #10
90 L98 TransAm
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Re: Battery Drain

i'm leaving the chime out for now. might leave it in if this was my daily driver but I drove the car less than 150 miles this year due to insane road construction where I live. washed it and put it away for winter today.

I would also leave the 20 A fuse for the interior lights out except I would lose use of the power door locks. I sure wish Pontiac had put on/off switches on the dome light and the cargo area light. it couldn't have cost much more to do so. maybe the GTAs got switches?

and i'm going to install a fuse for my auxiliary inline Walbro fuel pump. it comes on when you turn the key to the first detent so it runs when you are trying to set radio presets, adjusting your sound system, etc..
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