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Old 08-17-2013, 07:49 PM   #1
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What is this thing on the battery tray?

This was my first attempt of posting a picture on this forum. On my 2002 TJ 4.0 with auto trans I had my battery out so I thought I'd remove the battery tray to scrub it down and repaint. There is a hole in the middle of the tray with a flat plastic gizmo fitted to it with two wires attached to it. Or should I say there was because I broke it. I don't see it anywhere in my Chilton book. Does anybody know what this is?

Also, underneath the tray is a triangular looking plastic thing. I'm assuming that is the vacuum canister I've heard other people refer to? Thanks for any advice you can give.
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Old 08-17-2013, 07:50 PM   #2
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Temp sensor I believe.

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Old 08-17-2013, 07:50 PM   #3
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BTW, I don't know why I called the thing underneath triangular. It's a rectangular looking plastic object.
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Old 08-17-2013, 07:57 PM   #4
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Yep that is the battery temperature sensor. It is there to insure the alternator doesn't overcharge the battery or charge it at too high of a rate which could overheat the battery & cause it to burst.
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Old 08-17-2013, 08:15 PM   #5
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Thanks for the info. I should have been more careful. It's $33 at Advance autoparts. That's Ok, I deserve this.
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Old 08-17-2013, 09:48 PM   #6
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Originally Posted by 2004CSOTP View Post
BTW, I don't know why I called the thing underneath triangular. It's a rectangular looking plastic object.

Yes the box is a vacuum canister
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Old 08-17-2013, 11:05 PM   #7
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Yes the box is a vacuum canister
The p.o. disconnected it. I imagine if I put a vacuum pump on it and it holds I should reconnect it?
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Old 08-18-2013, 07:17 AM   #8
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Yes I would
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Old 08-18-2013, 05:21 PM   #9
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I put a vacuum pump on the canister and it held vacuum so I reconnected it. I got the temp sensor from Advance Auto Parts and put it all back together. The Jeep's running good. Thanks all for the info.
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Old 08-18-2013, 05:22 PM   #10
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Originally Posted by Jerry Bransford View Post
Yep that is the battery temperature sensor. It is there to insure the alternator doesn't overcharge the battery or charge it at too high of a rate which could overheat the battery & cause it to burst.
I thought it was a pressure sensor that will close the circuit in a roll over?
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Old 08-18-2013, 07:39 PM   #11
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I thought it was a pressure sensor that will close the circuit in a roll over?
Nope, it's a temperature sensor as described above.

And if you installed an aftermarket switch to cut the power in a rollover, you'd want it to open the circuit, not close it.
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Old 08-19-2013, 08:51 PM   #12
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The vacuum line going to the canister was blocked off with a screw and there were no vacuum leaks. I drove it about 100 miles today after removing the screw and reconnecting the canister. I didn't notice any difference in how it ran which really makes me wonder why it was disconnected in the first place. Also, I have never owned a vehicle with a battery temperature switch and wonder if exploding batteries is something common to Jeeps.
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Old 08-19-2013, 08:55 PM   #13
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That you have never noticed a battery temperature sensor doesn't mean they aren't commonly installed. Once again, it is there to prevent the alternator from overcharging the battery or charging it at two fast of a rate. All three of my vehicles have one.

The vacuum cannister is there so the HVAC controls can stay put as the engine vacuum level changes. What would cause engine problems is if the hose that connects the cannister to the engine were to be disconnected, causing a vacuum leak.
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Old 08-21-2013, 12:51 PM   #14
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Does every TJ have this sensor? I've pulled my battery out and didn't see anything like this.

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