Billybob wrote:
Yeah the BCM controls the timing.....unlikely that this is an item that would be a Dealer programming option....probably a fire hazard in the mirrors and rear glass heater if power is ON for too long.
Understood, and I agree with your reasoning on that. Thing is, it's not really much different if I keep having to turn the defroster back on every 5 minutes; they're going to get just as warm either way.
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The Theory of Operations section of the manuals does refer to the "programmed" value of ten minutes in the BCM so it should in theory be possible to re-program this value.
Ah, good, my observations were in line with the behaviour described in the manual I didn't bother to verify them against
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If you do not have the Wiring Diagrams...download the 2005 KJ Service Manual which includes the Wiring Diagrams at:
http://www.colorado4wheel.com/manuals/Jeep/KJYep, have those, but thanks for the pointer.
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Section 8g Heated Systems explains the operation...section 8W is the Wiring Diagram section.
The wiring diagrams have a Component Location section where you can find where the Defroster Relay is located on the rear of the interior fuse panel ie. the Junction Block.
Looking at pages 8W-48-2 and 8W-62-2 you can see that the BCM supplies Ground to the Defroster Relay on pin 85 to energize the Defroster Relay. You could try putting a large capacitor across pins 85 (minus) and 86 (positive) so that the capacitor charges up when the relay is energised and then keeps the relay energised for a while after power is dropped.
Not sure what capacitor to try....probably around 100 micro Farads but this would need some experimentation. Adding Capacitors in parallel adds up the capacitance. The BCM may pick up that this is happening and may complain about it. To much capacitance and the initial surge current could blow a fuse!
Thought about doing this, but my general apprehension towards electrical modifications (it's not a fear or misunderstanding of electrical and electronic theory; rather, I've had too many vehicles with poorly-hacked electrical systems and don't want to contribute to potential future electrical problems) has me somewhat cold on the idea.
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Or else rather fit a large-ish toggle switch to bypass the relay and directly pass +12 volts to the heated elements....or use a small switch and have it control a separate new relay.
The Dark Blue/White wire coming off the Junction Block C2 pin 2 can be cut and connected to the Common pole of your toggle switch.
The one side of the toggle switch gets connected back to the cut wire going off to the heated elements so that in this position all is as it has been.
The other side of the Toggle switch must go to a switched +12 volt position somewhere so that if you toggle to this side the heated elements pick up their power from +12 volts directly and bypasses the relay completely...power is not maintained when Jeep is switched off so as to stop your battery going flat. I would use an Inline 30 Amp Fuse to pick up this power at RUN F921 on page 8W-1023.
Totally agreed on having this be an ignition-switched mod, and for exactly the reasons you describe. It's also one reason I'd prefer to not go the capacitor route, since that would need to be discharged when the ignition was turned off. It's doable, but a bit more than I'd like to get into if it can be done otherwise.
So it looks as though altering the BCM's programming is probably the 'cleanest' method. I've found a small amount of info on people who are doing this for other FCA vehicles, but nothing specific to the KJ. Might give a couple of them a shout and see if they know anything I don't; if that doesn't pan out, the beefy switch and fuse may start looking appealing