Jebiruph
Well-Known Member
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This problem seems to be occurring more often. The JL/JT won't start (hot or cold) and the system electronics are going crazy. Jumpstarting doesn't work and the tow to the dealer results in a new aux battery. A few days later the same thing happens again, won't start, flashing electronics, towed to the dealer who finds and replaces another bad aux battery. This cycle continues until the dealer finds an replaces the bad high capacity fuse array with the blown N3 fuse.
Here's how the N3 fuse gets blown. I've modified my battery cable diagram to show the battery cables disconnect from the main battery. You can see that when the negative cables are disconnected from the main battery, the aux battery negative cable is still connected to ground. When the positive cable is removed from the main battery, the aux battery positive is still connected to it. At this point, it will look like battery power is completely disconnected, but if the positive cable is allowed to contact ground, it will create a short circuit from ground to the aux battery positive terminal and blow the high capacity N3 fuse.
There is not an immediate impact when the N3 fuse blows, but the aux battery and system electronics are now isolated from the alternator and the main battery. Everything will work as normal until the aux battery no longer has enough charge left to power up the electronics, resulting in the flashing system electronics and an inoperative jeep.
With the system electronics and the aux battery isolated from the main battery, connecting a charger to or trying to jump start from the main battery does not help, you need to get power to the N1 terminal. This can be done by using a jumper from the main battery positive to N1, but the aux battery ground cable needs to be completely disconnected from ground first. Otherwise the depleted aux battery will be trying to charge through the jumper, taking power from the system electronics and possibly exceeding the capacity of the jumper wire used. A fused bypass jumper (https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/post-423590) can be used, but this application may exceed the capacity of a 30A fuse.
Edit - To make sure the aux battery is completely disconnected, disconnect both negative cables like this.
Edit - If the N3 fuse (or any of the high capacity fuses) is blown, the whole fuse array has to be replaced. There are 2 different fuse arrays to accommodate the 2 different radiator fans.
fuse array with 60A fan - 68368853AA
fuse array with 100A fan - 68368854AA
Here's how the N3 fuse gets blown. I've modified my battery cable diagram to show the battery cables disconnect from the main battery. You can see that when the negative cables are disconnected from the main battery, the aux battery negative cable is still connected to ground. When the positive cable is removed from the main battery, the aux battery positive is still connected to it. At this point, it will look like battery power is completely disconnected, but if the positive cable is allowed to contact ground, it will create a short circuit from ground to the aux battery positive terminal and blow the high capacity N3 fuse.
There is not an immediate impact when the N3 fuse blows, but the aux battery and system electronics are now isolated from the alternator and the main battery. Everything will work as normal until the aux battery no longer has enough charge left to power up the electronics, resulting in the flashing system electronics and an inoperative jeep.
With the system electronics and the aux battery isolated from the main battery, connecting a charger to or trying to jump start from the main battery does not help, you need to get power to the N1 terminal. This can be done by using a jumper from the main battery positive to N1, but the aux battery ground cable needs to be completely disconnected from ground first. Otherwise the depleted aux battery will be trying to charge through the jumper, taking power from the system electronics and possibly exceeding the capacity of the jumper wire used. A fused bypass jumper (https://www.jlwranglerforums.com/forum/threads/3-6l-ess-aux-battery-bypass.17293/post-423590) can be used, but this application may exceed the capacity of a 30A fuse.
Edit - To make sure the aux battery is completely disconnected, disconnect both negative cables like this.
Edit - If the N3 fuse (or any of the high capacity fuses) is blown, the whole fuse array has to be replaced. There are 2 different fuse arrays to accommodate the 2 different radiator fans.
fuse array with 60A fan - 68368853AA
fuse array with 100A fan - 68368854AA
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