Battery drains overnight

MICHAEL GOSNEY

MEMBER
2004 JEEP GRAND CHEROKEE
4.7L
V8
4WD
AUTOMATIC
180,000 MILES

I have a friends JGC Overland that has been giving me fits with diagnosing what is causing the un-metered yet overnight draining of the battery. A rear passenger door sensor is showing when closed, I can remedy that, will that tell the ECU (ECM) to essentially stay "awake"long enough to drain the battery that quick? I know that a 50ma draw is acceptable and I have not metered it yet to see the actual number of ma being drawn but I am guessing 250+ in order to drain overnight. They have put a bunch of money into this rig and want as little as possible to continue. One other thing I noticed is the security system red light is on "top"of dash and is a steady on instead of blinking, is that unusual? Any help is good so as to hopefully save them some money. Thank you.

Thursday, October 18th, 2018 AT 4:00 PM

3 Replies

KEN L

MASTER CERTIFIED MECHANIC
54,137 POSTS

It sounds like a weak battery. The first thing I would check is to load test the battery let's use this guide to confirm. If okay it does sounds like the car is not "sleeping" you will need to scan the CAN system to see what is going on but if I had the guess it sounds like the rear door latch is having an issue not closing the protocol.

https://www.2carpros.com/articles/car-battery-load-test

This may help as well:

https://www.2carpros.com/articles/car-battery-dead-overnight

Please run down these guides and report back.

Cheers, Ken

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Saturday, October 20th, 2018 AT 11:11 AM

MICHAEL GOSNEY

MEMBER
16 POSTS

Thank you Ken, they do not use the vehicle now and it has had the problem for at least two years. Two years ago, I bought a new battery for it and it was draining it instantly so I suggested unhooking it for the time being. Well, after a while they left it connected for a long time which drained it so far that in less than the two years, it will not take a charge anymore. I have told them to get a new one again so that I can test things properly with strong voltage. I need to run it so I can test the alternator
and with most cars newer than 2000, maximum voltage is required to operate all the on board systems. I am suspect of the rear passenger door indicator switch being bad since I have not found bad wires or connections.
But again, thank you for your input and once a new battery is obtained, I can get to the real cause (causes) for the drain.

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Saturday, October 20th, 2018 AT 9:48 PM

KEN L