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Grand Cherokee Battery Drain

Old 11-14-2016, 06:18 PM
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Default Grand Cherokee Battery Drain

Hi folks.
My 2004 Grand Cherokee has a battery drain if I don't drive the car every 4 or 5 days.
I'm not very sharp when it comes to electrical, but here's what I discovered. In pulling the fuse for the O2 sensor, it reads 1.6 Colts across the posts. Also I get .3 volts across the posts for the rear power outlet with fuse pulled.
Is this normal? Does the O2 sensor have a memory that requires voltage going to it?
Thanks in advance for any and all help.
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Old 11-15-2016, 04:23 AM
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The 02 sensor has a heater that requires current. That's what the fuse is for. The signal back to the PCM is in millivolts.
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Old 11-15-2016, 09:14 AM
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Welcome to the forum!

The first steps are to verify that the generator is charging properly and that the battery is good.

After driving the vehicle and the engine at a high idle, about 2,000 rpm, with all big current consumers turned off, verify that the voltage measured on the battery terminals is about 13.8 VDC. If so, then the generator is probably good. If not, then find out why the generator isn't topping off the battery.

Then the battery needs to be verified as good. Any store selling batteries has a multimeter-type tester that will show good or bad. I used to design those and am not sold on those being appropriate for go / no go testing on batteries.

In this case it sounds like the Jeep is used infrequently. If so, park the Jeep. Disconnect the battery, then measure the battery voltage at-least every day, more frequently is battery. The battery voltage will have an initial sag, from 13.8 to 12.5, as the surface charge from the generator dissipates. It should then hold the voltage with a very, very slow decay. If it drops more quickly then it is bad. If it passes this then it might still be bad.

My favorite battery test is to use a carbon pile load, set to drain a good battery in 20 hours and measure the run time. More than 10 hours is considered still good.
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Old 11-15-2016, 10:12 AM
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I have a similar issue, I picked up one of those solar chargers at harbor freight. I also have one of their 6 dollar battery tenders that Iplug in when I expect the jeep to be sitting for a bit.
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Old 11-19-2016, 09:36 PM
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Shouldn't be anything to do with the O2 sensor... check the Power Draw relay under the hood (diagram should tell which one it is, as well as the manual). The relay provides power to everything that doesn't require a key to function (power seats, radio memory, memory seats and mirrors, security system, keyless entry, power door locks, etc). I had a problem with that on my old '94 ZJ Grand Cherokee and replaced the relay, never had a problem afterwards.
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Old 11-20-2016, 12:07 PM
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Lots of guessing here but not too much troubleshooting. Start with an inline current meter to the battery and see how much is draining. Over 14mA is too much.

But, if you twist my arm and I had to guess, I would suspect the switches on the locks on the drivers, front passenger, and perhaps rear door are stuck in the unlocked position. This won't let the bcm set the alarm usually and the bcm stays 'awake' drawing too much current. Usually there is an issue with the interior lights staying on after the doors are closed and locked, until they time out.

Last edited by 97grand4.0; 11-20-2016 at 12:59 PM.
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Old 11-21-2016, 10:37 PM
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I'd honestly start with the power draw relay before anything else. It's the easiest thing to replace.
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Old 11-22-2016, 03:44 AM
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Originally Posted by 94zj318 View Post
I'd honestly start with the power draw relay before anything else. It's the easiest thing to replace.
Kidding I hope. Power Draw Relay? Exactly what would that be.. the relay for the power draw? What is it drawing power from? And why does it need a relay?

Last edited by 97grand4.0; 11-22-2016 at 03:47 AM. Reason: confusion
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Old 11-22-2016, 01:53 PM
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Default Optima battery and high amp alternator

Hey Bro, don't know if this helps but if you just want to throw some $$$ at the problem, go with a high-amp alternator and a nice yellow Optima battery. (You may have to turn the alt case housing 90 degrese to get your connectors to line up) but my '96 ZJ used to drain every few days too - never could figure out why (best guess is the pwer-amp aftermarket sound system) but replacing the alt with a 90 amp model and the Optima battery did the trick - no drains since then!


(more $$$ than time!)
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Old 11-22-2016, 07:27 PM
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Originally Posted by 94zj318 View Post
I'd honestly start with the power draw relay before anything else. It's the easiest thing to replace.
There ain't no such thing! There are several YouTube videos that show how to do a parasitic draw test. Basically, you disconnect the battery positive cable and put an ammeter between the cable and the post. Then start pulling fuses one at a time to see which circuit is drawing current. You have to make sure the doors are closed and the interior lights are off or they will show a draw. Don't forget the underhood light if you have one. As was stated, more than 14 milliamps is too much. That's for the memory for the radio and PCM. When you find the fuse that drops the draw the most, that's your culprit.

You should use an ammeter that handles at least 20 amps.

Last edited by dave1123; 11-22-2016 at 07:32 PM.
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Old 11-22-2016, 07:59 PM
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With all these guru's I'm surprised no one has sugested checking the balance of the muffler bearing. If it's slightly off ballence that could draw a lot of power and throw the whole system out of wack!
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Old 11-23-2016, 06:38 AM
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Originally Posted by jon-d View Post
With all these guru's I'm surprised no one has sugested checking the balance of the muffler bearing. If it's slightly off ballence that could draw a lot of power and throw the whole system out of wack!
I agree with that. The power draw relay is constantly surveying the pcm exhaust paramaters.
Best to bring it to some place that specializes in muffler systems like Midas or Monroe and tell them the whole story. Ask for the complete replacement including exhaust manifolds. This should centralize the muffler bearings and reset the pcm. Should probably have them lube the alternator resistor bank as well.
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Old 11-23-2016, 07:33 AM
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While it is not cool w/ the Feds and the EPA, people who have done the muffler bearing elimination modification have had positive vehicle results, w/ the added benefits of better personal health and fuller hair.
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Old 11-23-2016, 11:21 AM
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Originally Posted by rbeard2 View Post
Hey Bro, don't know if this helps but if you just want to throw some $$$ at the problem, go with a high-amp alternator and a nice yellow Optima battery. (You may have to turn the alt case housing 90 degrese to get your connectors to line up) but my '96 ZJ used to drain every few days too - never could figure out why (best guess is the pwer-amp aftermarket sound system) but replacing the alt with a 90 amp model and the Optima battery did the trick - no drains since then!


(more $$$ than time!)
Did you stop to think it could have been your alternator that was the problem in the first place? A bad diode trio could have kept the field energized all the time.
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