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Eliminating Defroster Timer
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=1&t=87609		 Page 1 of 1
Author:  casm [ Wed Dec 27, 2017 11:34 pm ]
Post subject:  Eliminating Defroster Timer
Ours is a 2005 CRD Limited, but given that this is probably controlled by the BCM I suspect that it may be a model-independent question.

What I'd like to do is change the behaviour of the defroster timer. Right now it seems to turn on for 10 minutes on the first press, then automatically turn off. Subsequent presses have it run for 5 minutes before turning off; shutting down the engine and restarting resets the behaviour to the initial 10-minute pattern.

What I'd like it to do is to just stay on when first pressed. If it turns off with the ignition, that's fine, but having to keep turning it on every 5 minutes in freezing rain so that the side mirrors don't ice over is both annoying and a safety issue since I have to take my eyes off the road to find the switch when I hear the relay click off.

Is there a good way to accomplish this, or is it something I'll just have to live with?
Author:  Billybob [ Thu Dec 28, 2017 6:49 am ]
Post subject:  Re: Eliminating Defroster Timer
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. 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.

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/KJ

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!

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. :wink:
Author:  casm [ Fri Dec 29, 2017 7:56 am ]
Post subject:  Re: Eliminating Defroster Timer
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.

Quote:
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 ;)

Quote:
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/KJ


Yep, have those, but thanks for the pointer.

Quote:
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.

Quote:
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. :wink:


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 ;)
Author:  joe_ [ Fri Dec 29, 2017 7:39 pm ]
Post subject:  Re: Eliminating Defroster Timer
casm wrote:
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.
I think the idea here is, with the timer, you can't accidentally leave it running and overheat stuff. Would be nice if they programmed it to stay on as long as the ambient temperature sensor in the grill is reading below, say, 40°F or 50°F.
Author:  tjkj2002 [ Fri Dec 29, 2017 10:03 pm ]
Post subject:  Re: Eliminating Defroster Timer
joe_ wrote:
casm wrote:
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.
I think the idea here is, with the timer, you can't accidentally leave it running and overheat stuff. Would be nice if they programmed it to stay on as long as the ambient temperature sensor in the grill is reading below, say, 40°F or 50°F.

You don't need the rear window defroster or side mirror heaters till the temps reach well under 20 degrees,and then you should not need it on for more then 10mins at most.
Author:  joe_ [ Sat Dec 30, 2017 12:23 am ]
Post subject:  Re: Eliminating Defroster Timer
Well under 20 degrees? Unless you're talking Celsius, I disagree. Water's long been frozen by 20°F. Even above freezing, it's useful for removing dew from the window in the morning or evaporating light rain (although moreso on vehicles without a rear wiper).

10 minutes at most? I've been in plenty of situations where I've needed it on for more than 10 minutes. So has the original poster:
casm wrote:
... but having to keep turning it on every 5 minutes in freezing rain so that the side mirrors don't ice over ...
Author:  WWDiesel [ Sat Dec 30, 2017 11:17 am ]
Post subject:  Re: Eliminating Defroster Timer
Just a thought! Has anyone with a DRBIII or similar device that can access the BCM checked to see if there is any adjustability in the heat length cycles for the defrosters in the BCM? :idea:
I know there are some things adjustable with a DRBIII! :roll:
Author:  casm [ Sun Dec 31, 2017 10:28 am ]
Post subject:  Re: Eliminating Defroster Timer
tjkj2002 wrote:
You don't need the rear window defroster or side mirror heaters till the temps reach well under 20 degrees,and then you should not need it on for more then 10mins at most.


Well, that was an easy fix! :roll:

In other news: a tech at one of the local dealers has agreed to take a look at what (if anything) might be changeable via DRB. I'll by swinging by with it later this week and will update once I know more.
Author:  WWDiesel [ Sun Dec 31, 2017 10:37 am ]
Post subject:  Re: Eliminating Defroster Timer
casm wrote:
tjkj2002 wrote:
You don't need the rear window defroster or side mirror heaters till the temps reach well under 20 degrees,and then you should not need it on for more then 10mins at most.


Well, that was an easy fix! :roll:

In other news: a tech at one of the local dealers has agreed to take a look at what (if anything) might be changeable via DRB. I'll by swinging by with it later this week and will update once I know more.

:D
Author:  casm [ Wed Jan 03, 2018 10:40 pm ]
Post subject:  Re: Eliminating Defroster Timer
Update:

The dealer tech took a look into changing the defroster timer behaviour today. His comment: it might be possible, but it's not clear to him which parameter(s) may need to be changed.

I'll drop an email out to some of the places that are offering FCA BCM tweaks in the next day or two and see what they may say.
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