Rear defroster? - JeepForum.com
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post #1 of 7 Old 09-07-2021, 05:48 AM Thread Starter
Adhtjk09
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1937 CJ2A 
 
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Location: Pittsburgh
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Rear defroster?

So I recently bought my liberty, now that colder weather has rolled around I needed the rear defroster. I hit the button on the knob. Needless to say no light came on and its not working. My initial thought was the fuse so I checked it, it looked fine. But I went ahead and replaced it to be sure. Still nothing... any suggestions?

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post #2 of 7 Old 09-07-2021, 06:14 AM Thread Starter
Adhtjk09
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Also checked the relay

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post #3 of 7 Old 09-07-2021, 06:44 PM
Rob K
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What year KK Liberty? Are your side mirror defrosters working? The relay sends power to all three defrosters.

Here's a wiring diagram for 2011. The defroster switch connects to the computer CAN data buss. If the switch is pressed the computer is monitoring that and sends info the TIPM(fuse block assembly). This activates the relay and sends power to the two fuses, 40amp rear defroster and 10amp for side mirrors defrosters.

I'd start with the simplest thing. Pull the fuse and probe the two connectors to see if you have power getting to one side of the fuse. If not then the relay is not being activated. Sounds like you may have swapped the relay already. After that you have to figure out why the computer and TIPM are not activating the relay. The most likely suspects are the switch and wiring connections. With computers a reboot sometimes fixes things. Chance are it won't fix your problem but it wouldn't hurt to disconnect the battery for a while so that the computer has to relearn everything when you power it back up. Worth a shot anyway.

If you had the right scanner to connect to the port under the dash you probably could test the switch. I've have never needed to look into buying a scanner yet so I don't know what is available and if consumers even have access to a scanner that will do diagnostic testing on the individual switches, sensors and modules.
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post #4 of 7 Old 09-07-2021, 07:35 PM Thread Starter
Adhtjk09
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Quote:
Originally Posted by Rob K View Post
What year KK Liberty? Are your side mirror defrosters working? The relay sends power to all three defrosters.

Here's a wiring diagram for 2011. The defroster switch connects to the computer CAN data buss. If the switch is pressed the computer is monitoring that and sends info the TIPM(fuse block assembly). This activates the relay and sends power to the two fuses, 40amp rear defroster and 10amp for side mirrors defrosters.

I'd start with the simplest thing. Pull the fuse and probe the two connectors to see if you have power getting to one side of the fuse. If not then the relay is not being activated. Sounds like you may have swapped the relay already. After that you have to figure out why the computer and TIPM are not activating the relay. The most likely suspects are the switch and wiring connections. With computers a reboot sometimes fixes things. Chance are it won't fix your problem but it wouldn't hurt to disconnect the battery for a while so that the computer has to relearn everything when you power it back up. Worth a shot anyway.

If you had the right scanner to connect to the port under the dash you probably could test the switch. I've have never needed to look into buying a scanner yet so I don't know what is available and if consumers even have access to a scanner that will do diagnostic testing on the individual switches, sensors and modules.
I believe disconnecting the battery will be my next step, thank you!

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post #5 of 7 Old 09-08-2021, 06:18 AM Thread Starter
Adhtjk09
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Quote:
Originally Posted by Adhtjk09 View Post
I believe disconnecting the battery will be my next step, thank you!

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I'm sorry I didn't finish answering your question, it is a 2011. I have heated mirrors but I do not believe they are working either. The actual knob works for changing air direction, but when pushing the button for defrost the light doesn't even come on

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post #6 of 7 Old 09-24-2021, 05:30 AM Thread Starter
Adhtjk09
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Location: Pittsburgh
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Update:
I checked fuses, relays, disconnected and reconnected the battery, and last but not least I've replaced the control unit. The button now illuminates but the defroster still doesn't work... I'm at a loss..

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post #7 of 7 Old 09-25-2021, 08:07 PM
Rob K
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So you fixed part of the problem. The next step is to use the schematic and a voltmeter to test your way through the circuit to see what is happening. Easiest thing is to test for 12v at the fuse. If you don't have 12v there then the relay is not turned on or possibly power is not getting to the relay. The other possibility is the the computer is not activating the relay for some reason. Then your looking at more in depth troubleshooting with a volt or ohm meter and a scanner of some type. I've never had to use a scanner so I can't offer advise on that.
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