Hi guys, things are not good. I left the car for a week and battery went dead. I think - no problem, old battery, time to get a new one. I've put the new battery in, drove the car, OK. Two days later I want to drive it again - the new battery is DEAD. Measure voltage - about 2.5V left. Remove battery, put ohmmeter between + and - cables, shows about 10ohms, looks like a short somewhere. No lights etc left on.
Any ideas what could be shorting the battery? If the short is in an unlucky place it could even caue some fire if the car is started and driven (?), so driving it could be a problem too. I don't really feel like having it towed to the dealer now, so any help is appreciated
thx
George
2002 Q45 dead battery - what could short it? HELP
When I first read your post I thought you said you put our ohm meter across the + and - of your battery and that's a huge no no and would have burned up your meter. If I'm reading you right you did that between your + and - cables after disconnecting them from your battery? Is that right?
10 ohms is not a sign of a short. There are many circuits that are low impedence that will show resistance from + to -. You need to hook up your battery and put an ammeter inline with either your negative OR the positive of your battery so the current your car is pulling/drawing is going through your ammeter. Do not put our ammeter from + to - or it will blow it up or burn up the fuse. Most typical ammeters will handle up to 10 amps on the proper setting and using the proper terminals. DO NOT ATTEMPT TO START THE CAR LIKE THIS OR YOU WILL BLOW YOUR METERS FUSE!
Leaving the key off and make sure you unplug your underhood light let the car sit with all doors shut so you "think" everything is off. Your amperage should settle down to a very low amount.
Here is a quote from an old post I did regarding amperage draws under various conditions on my '94 Q45. It should give you a good idea of where your car should be if it was not draining the battery. If you have more than about .05-.07 amps draw from your battery with everything off after a couple of minutes there is something draining the battery so start pulling fuses for various circuits to narrow it down. I give several examples in my testing on what to disconnect and it's effect.
=====OK, I have some baseline numbers from my '94 that's currently great in the electrical department. I pulled the negative terminal and installed my Fluke ammeter inline. Leads in the 10 amp terminals on the meter. You could use the positive as well, would make no difference. I just used the negative as it doesn't have all the other wires connected to it. Negative meter lead to B- and the meter positive lead to the negative battery cable. If you get these backwards you will just read negative amps, no big deal.
Upon connection the dome turned on and stayed on due to my aftermarket alarm until I armed and disarmed it. Then it turned off. Also, there are apparently some systems that operate for a couple minutes upon connection of power as the amps take about 1-2 minutes to stabilize at the low level.
Initial connection w/alarm disarmed, dome light on -> 3 amps, settled to 2.6 amps
Aftermarket alarm armed, dome light off -> .24 amps then settled to .066 amps after approx. 1 minute.
Alarm disarmed, dome light off -> .063 amps after 1 minute
Start pulling large fuses in under hood fuse compartment, unless noted I reinstalled the fuses prior to pulling the next fuse/relay"IGN SW" 30A fuse -> .056 amps"ENG CONT" 25A fuse -> no change"INJ" 25A fuse -> no change"COND FAN" 30A fuse -> no change"MAIN" 75A fuse -> .043 amps"MAIN" and "IGN SW" -> .035 amps*When "MAIN" reinstalled amps were at .5 amps 2 minutes then settled back to .063 indicating that a circuit was operating for a couple minutes upon power up, ECU?"Power window" fuse -> no change"Anti Skid" fuse -> no change"Blower Motor" -> no change
Small underhood fuses"Eng Cont" 10A fuse -> no change"Fog Lamp" 15A fuse -> no change"Room Lamp" 10A fuse -> no change (unless the dome light was on already)"Tail Lamp" 10A fuse -> no change"ALT (S)" 10A fuse -> no change"Hazard" 10A fuse -> no change"Horn" 15A fuse -> no change"Headlamp LH" fuse -> no change"Headlamp RH" fuse -> no change
Relays underhood in junction box (same box as above)"Anti Theft" -> no change"Cond Fan" -> no change"Cruise Cont" -> no change"Inhibit" -> no change"A/C" -> no change
MiscellaneousTrunk open w/trunk lamp on -> .4 amps (amps fluctuating +/-)Room lamp fuse out, door open -> .233 amps (might be alarm LED drawing)Room lamp fuse out, door open, park lights on -> 6.2 ampsHeadlights on -> Exceeded 10 amps, couldn't get accurate reading
This should give you a good start on tracing the amp draw. I didn't pull the two really large fuses next to the fuse/relay box (100A+) or the two black/white wires plugged in at the B+ terminal.
10 ohms is not a sign of a short. There are many circuits that are low impedence that will show resistance from + to -. You need to hook up your battery and put an ammeter inline with either your negative OR the positive of your battery so the current your car is pulling/drawing is going through your ammeter. Do not put our ammeter from + to - or it will blow it up or burn up the fuse. Most typical ammeters will handle up to 10 amps on the proper setting and using the proper terminals. DO NOT ATTEMPT TO START THE CAR LIKE THIS OR YOU WILL BLOW YOUR METERS FUSE!
Leaving the key off and make sure you unplug your underhood light let the car sit with all doors shut so you "think" everything is off. Your amperage should settle down to a very low amount.
Here is a quote from an old post I did regarding amperage draws under various conditions on my '94 Q45. It should give you a good idea of where your car should be if it was not draining the battery. If you have more than about .05-.07 amps draw from your battery with everything off after a couple of minutes there is something draining the battery so start pulling fuses for various circuits to narrow it down. I give several examples in my testing on what to disconnect and it's effect.
=====OK, I have some baseline numbers from my '94 that's currently great in the electrical department. I pulled the negative terminal and installed my Fluke ammeter inline. Leads in the 10 amp terminals on the meter. You could use the positive as well, would make no difference. I just used the negative as it doesn't have all the other wires connected to it. Negative meter lead to B- and the meter positive lead to the negative battery cable. If you get these backwards you will just read negative amps, no big deal.
Upon connection the dome turned on and stayed on due to my aftermarket alarm until I armed and disarmed it. Then it turned off. Also, there are apparently some systems that operate for a couple minutes upon connection of power as the amps take about 1-2 minutes to stabilize at the low level.
Initial connection w/alarm disarmed, dome light on -> 3 amps, settled to 2.6 amps
Aftermarket alarm armed, dome light off -> .24 amps then settled to .066 amps after approx. 1 minute.
Alarm disarmed, dome light off -> .063 amps after 1 minute
Start pulling large fuses in under hood fuse compartment, unless noted I reinstalled the fuses prior to pulling the next fuse/relay"IGN SW" 30A fuse -> .056 amps"ENG CONT" 25A fuse -> no change"INJ" 25A fuse -> no change"COND FAN" 30A fuse -> no change"MAIN" 75A fuse -> .043 amps"MAIN" and "IGN SW" -> .035 amps*When "MAIN" reinstalled amps were at .5 amps 2 minutes then settled back to .063 indicating that a circuit was operating for a couple minutes upon power up, ECU?"Power window" fuse -> no change"Anti Skid" fuse -> no change"Blower Motor" -> no change
Small underhood fuses"Eng Cont" 10A fuse -> no change"Fog Lamp" 15A fuse -> no change"Room Lamp" 10A fuse -> no change (unless the dome light was on already)"Tail Lamp" 10A fuse -> no change"ALT (S)" 10A fuse -> no change"Hazard" 10A fuse -> no change"Horn" 15A fuse -> no change"Headlamp LH" fuse -> no change"Headlamp RH" fuse -> no change
Relays underhood in junction box (same box as above)"Anti Theft" -> no change"Cond Fan" -> no change"Cruise Cont" -> no change"Inhibit" -> no change"A/C" -> no change
MiscellaneousTrunk open w/trunk lamp on -> .4 amps (amps fluctuating +/-)Room lamp fuse out, door open -> .233 amps (might be alarm LED drawing)Room lamp fuse out, door open, park lights on -> 6.2 ampsHeadlights on -> Exceeded 10 amps, couldn't get accurate reading
This should give you a good start on tracing the amp draw. I didn't pull the two really large fuses next to the fuse/relay box (100A+) or the two black/white wires plugged in at the B+ terminal.
Re: (qsiguy)
Thanks qsiguy, very usefull data! (Yes, I did measure ohms on the car, not battery).
Putting the ammeater in-line I'm getting similar numbers to yours, except that when the car is settled with the alarm disabled 0.035, with alarm armed and the car locked 0.165, which sounds high. But also not high enough to drain the battery in a few days (assuming 200Ah battery - would take 50 days to drain to 0Ah with 0.165A). So either there was some transient problem which went away or there is something which can not be explained yet...
Putting the ammeater in-line I'm getting similar numbers to yours, except that when the car is settled with the alarm disabled 0.035, with alarm armed and the car locked 0.165, which sounds high. But also not high enough to drain the battery in a few days (assuming 200Ah battery - would take 50 days to drain to 0Ah with 0.165A). So either there was some transient problem which went away or there is something which can not be explained yet...