Parasitic Power Drain
Thread Starter
1st Gear
Joined: May 2015
Posts: 1
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From: The Woodlands TX
Parasitic Power Drain
Have a 2000 convertible. The battery drops about .3 volts every 24 hours. Headlamp motors are both pulling about .3 mA each, cooling fan is pulling 7 mA, approach lights are pulling about .5mA, alternator is pulling about .5 mA with switches and key off
Problem seems systemic to the entire electrical system. Have started the process of cleaning all the grounds. Is there anything else that could create this problem?
Problem seems systemic to the entire electrical system. Have started the process of cleaning all the grounds. Is there anything else that could create this problem?
Le Mans Master
Joined: Mar 2011
Posts: 6,835
Likes: 302
From: Columbia SC
Here is my input for drain.
Suggest you remove the hood light bulb first so it does not provide a drain.
For measuring battery drain I would hook up an ammeter to the negative side of the battery by removing the negative cable and measure between the cable and the negative battery post.
When you connect the ammeter the car should draw several amps until it goes into "sleep" mode which can take several minutes. Normal sleep mode drain should be 30 milliamps or less by GM standards. You will need an ammeter that can transition from whatever the drain is down into the sleep mode. If you have a drain I suggest the following:
Once you determine you have a drain with an ammeter what I recommend first is to listen to each fuse box and see if you hear any relays operating. If not, then place your hand on each relay to see if any of them feel hot. That can be the start if you find something like that is happening.
If nothing shows up you can hear or feel then I recommend you separate the two fuse boxes from each other. This is easy and done by removing the Red cable from the engine fuse box that feeds the passenger fuse box. It is on the right rear side of the engine fuse box. There is a stud there where the large Red wire from the battery connects. Just remove the nut and disconnect the large Red wire feeding the passenger fuse box and reattach the Red battery cable. NOTE: I would recommend disconnecting the negative ammeter hookup when working on the positive side doing this.
What you will be doing is measuring the drain with an ammeter to see if disconnecting the passenger fuse box causes the drain to go away or not. By depowering the passenger fuse box you will depower the BCM which controls the sleep mode so do not expect the sleep mode to happen.
If removing the feed to the passenger fuse box you then see you have eliminated the drain then you know it is something related to those circuits. If it does not reduce the drain then you know it is related to the engine fuse box. It could be a rare case where you have some drain via both fuse boxes and we can deal with that if you think it is the case.
Just so you know, even though it may appear to be a problem in the engine or interior area the fuse boxes do feed circuits to each other that are not affected by separating the boxes. So, separating the fuses boxes can tell you how to narrow down your search but still not where the issue may be. That is where the schematics come into play to track down the “real” culprit. Hope that makes sense.
Once you basically know where it is then you can remove fuses and relays to see where the drain is coming from.
PS: There are cases where the alternator causes a drain so it can be disconnected and see if the drain drops.
Suggest you remove the hood light bulb first so it does not provide a drain.
For measuring battery drain I would hook up an ammeter to the negative side of the battery by removing the negative cable and measure between the cable and the negative battery post.
When you connect the ammeter the car should draw several amps until it goes into "sleep" mode which can take several minutes. Normal sleep mode drain should be 30 milliamps or less by GM standards. You will need an ammeter that can transition from whatever the drain is down into the sleep mode. If you have a drain I suggest the following:
Once you determine you have a drain with an ammeter what I recommend first is to listen to each fuse box and see if you hear any relays operating. If not, then place your hand on each relay to see if any of them feel hot. That can be the start if you find something like that is happening.
If nothing shows up you can hear or feel then I recommend you separate the two fuse boxes from each other. This is easy and done by removing the Red cable from the engine fuse box that feeds the passenger fuse box. It is on the right rear side of the engine fuse box. There is a stud there where the large Red wire from the battery connects. Just remove the nut and disconnect the large Red wire feeding the passenger fuse box and reattach the Red battery cable. NOTE: I would recommend disconnecting the negative ammeter hookup when working on the positive side doing this.
What you will be doing is measuring the drain with an ammeter to see if disconnecting the passenger fuse box causes the drain to go away or not. By depowering the passenger fuse box you will depower the BCM which controls the sleep mode so do not expect the sleep mode to happen.
If removing the feed to the passenger fuse box you then see you have eliminated the drain then you know it is something related to those circuits. If it does not reduce the drain then you know it is related to the engine fuse box. It could be a rare case where you have some drain via both fuse boxes and we can deal with that if you think it is the case.
Just so you know, even though it may appear to be a problem in the engine or interior area the fuse boxes do feed circuits to each other that are not affected by separating the boxes. So, separating the fuses boxes can tell you how to narrow down your search but still not where the issue may be. That is where the schematics come into play to track down the “real” culprit. Hope that makes sense.
Once you basically know where it is then you can remove fuses and relays to see where the drain is coming from.
PS: There are cases where the alternator causes a drain so it can be disconnected and see if the drain drops.
