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  #13  
Old 06-01-2013, 06:36 AM
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Re: Flat Towing Problem – Jeep Grand Cherokee 2014

Installed diodes. And I had the same thought and mentioned it to the dealer. But at this point the diodes do not seem to be the problem. I am not saying that diodes can't short but so far I have not found a single case of shorted diodes. My installer has found some "open" diodes and they typically fail immediately. If you know of any "shorted" diodes I would like to hear about it.

I am reading about 2014 GC "loose grounds" causing problems that are identical to the same symptoms I had. Could be that flat towing and an instrument panel full of warning lamps may only be coincidental.

Even more of a mystery is the fact that the fault codes of "low voltage" are inconsistent with the engine starting with no hesitation. But the "low voltage" fault code does show up with the loose ground problem and the batteries are not discharged.

I have added a charging circuit to make sure that the battery stays charged just in case my problem is battery related. It is conceivable that IF the vehicles computers are running in the background then over time they would discharge the battery. But the two dealers I have spoken to have not been able to confirm what would be using power.

If I have a "loose ground" problem I am expecting to see the problem again. And since we are on the road it makes it more difficult to troubleshoot with the same dealer.

This morning I am going to look at the ground connections that I can find to see if there is anything obviously loose or corroded (on a vehicle with 1,600 miles?). Otherwise, time will tell if we still have a problem. Thanks for your input.
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Old 06-01-2013, 10:35 AM
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Re: Flat Towing Problem – Jeep Grand Cherokee 2014

Admit do not know much about MOPAR alternators but in GM CS-130 and CS-144s I have seen the regulator fail which turns the alternator on max.

Years ago I remember havng a shorted diode in a 10DN though it is more common for them to fail open.

My concern is a loose ground particularly to the battery could cause major surges that could affect anything including the alternator. Can happen in a fraction of a second particularly with an alternator capable of over 150 amps. Milage is irrelevant.

Back in the 70s with 55 amp alternators and rugged components it was a known issue but rare (cars then also had a heavy short ground wire from the battery to the block & much smaller chassis grounds). Today with three times the alternator power, remote batteries, and 22 nanometer electronics, welll...

ps have never measured the heep but for my GM cars the quiescent spec is "under 50 milliamps" and mine usually run 17-20. A 1970 mechanical clock will draw more.

Can only say what I would do but if buying a '14 I would torque all of the grounds (including under the seat) and have the dealer check for codes before ever leaving the lot. And then I would not worry about it (could set my OBD reader to record high and low voltage excusions but why ?)
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Old 06-01-2013, 08:49 PM
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Re: Flat Towing Problem – Jeep Grand Cherokee 2014

<!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <wontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]-->I did stick my head under the hood this morning and found four grounds and put a socket on them. I did not feel like any of them were “loose”. One thing I noticed is that the grounds were screwed to the frame and as you attempted to tighten the bolt the wire attachment ring terminals also rotated pulling on the wire(s). So I got a screwdriver and attempted to wedge it in a way to keep the terminal rings from turning as I tightened the bolt. Awkward and it didn’t leave me thinking I had the bolt as tight as it might go but it’s probably tight enough. What I did not do is remove the bolts and clean the terminals. All this work is taking place in a parking lot so I’ll leave that step to the Jeep dealer if we have another episode. <!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]-->
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Old 06-01-2013, 11:11 PM
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Re: Flat Towing Problem – Jeep Grand Cherokee 2014

During 40 years in electronic repair I have seen shorted diodes.....but I have not seen any of these heavy duty, dual input - single output diodes shorted input to input where the coach system could feed back into the Jeep system. That don't mean it can't happen but I have not seen that. I agree that most diode failures are opens.

When I started to wire my '11 JGC the first thing I did was remove a tail light bulb and then turn the ignition to ON. I saw a message in the EVIC that the Left Rear tail light was out. It flashed up there for a few seconds and then it was gone. That made me think that the tail light circuit was monitored by some system in the Jeep. I was afraid of wiring the coach lights to the Jeep lights with diodes because the sensor could be on the ground side of the tail light circuit and I also had a ground back to the coach through the tow bar. Anyway, being a coward I opted to install the Blue Ox separate light bulb kit.

I had used the diodes on my two previous tow cars, a Geo Tracker and a Jeep Liberty, but with all of the electronics, data busses, and processors on these new vehicles I was leery of inducing any foreign voltages and grounds into the system.
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Old 06-02-2013, 07:44 AM
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Re: Flat Towing Problem – Jeep Grand Cherokee 2014

I actually think that it's the braking system causing his problems. First, it's the only thing different than stock.

Second, reading about how this device is installed...it activates the towed vehicles brakes (so I wonder...does that actually activate the towed vehicles Brake Lights...and by design...does that mean it activates the towed vehicles brake light switch).

Now without a wiring diagram...I think the following is happening... Brakes activate...brake light switch on towed vehicle is actuated...computers in towed vehicle wake up... and somehow this is tripping up computer logic...etc.

So...I think the condition is because of the computers yes...but not their fault. Something tells me these new Jeeps don't have a wire going direct from battery through brakelight switch to brakelight bulb....

Instead, I picure activating the brakelight switch sends a signal to a logic circuit in the body control computer...that isn't designed for extended "brake light with vehicle in motion but engine not running" scenarios...
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Old 06-02-2013, 07:48 AM
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Re: Flat Towing Problem – Jeep Grand Cherokee 2014

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Originally Posted by SteveCG View Post
Installed diodes. And I had the same thought and mentioned it to the dealer. But at this point the diodes do not seem to be the problem. I am not saying that diodes can't short but so far I have not found a single case of shorted diodes. My installer has found some "open" diodes and they typically fail immediately. If you know of any "shorted" diodes I would like to hear about it.

I am reading about 2014 GC "loose grounds" causing problems that are identical to the same symptoms I had. Could be that flat towing and an instrument panel full of warning lamps may only be coincidental.

Even more of a mystery is the fact that the fault codes of "low voltage" are inconsistent with the engine starting with no hesitation. But the "low voltage" fault code does show up with the loose ground problem and the batteries are not discharged.

I have added a charging circuit to make sure that the battery stays charged just in case my problem is battery related. It is conceivable that IF the vehicles computers are running in the background then over time they would discharge the battery. But the two dealers I have spoken to have not been able to confirm what would be using power.

If I have a "loose ground" problem I am expecting to see the problem again. And since we are on the road it makes it more difficult to troubleshoot with the same dealer.

This morning I am going to look at the ground connections that I can find to see if there is anything obviously loose or corroded (on a vehicle with 1,600 miles?). Otherwise, time will tell if we still have a problem. Thanks for your input.
I also can only guess at this without the engineering drawings/logic circuit and coding... Your "Low voltage" requirements to set that error code are probably a higher voltage than the bare minimum to start the vehicle. Low voltage doesn't necessarily equal "no voltage"...it just means that an error checking piece of code didn't have it's minimum voltage met...hence the "low voltage" is set. Happens on aircraft all the time...we'll trip a "error" code in the computer like "low oxygen pressure" when there is still plenty on the analog gauge, but it's outside the coding threshold for that error signal in the digital system.
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Old 06-02-2013, 09:10 PM
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Re: Flat Towing Problem – Jeep Grand Cherokee 2014

Thanks for the reply’s. We towed 4 hours today with the new charge line charging the toad battery. At arrival we had no problem. In my mind the problem isn’t yet solved but it was helpful that we weren’t burdened with having to run to a Jeep dealer.

I sure would not argue against installing separate bulbs as I did that with my last toad. By doing so it would eliminate the potential of diode failure or as you describe bypassing the risk of some unknown circuit design. I did not do it on this 2014 as I thought the space was too tight. Maybe I need to look at it again and also see if there are smaller bulb configurations that might better fit.

The 2014 GC brake lights are not operative when the ignition is in the “off” position. This means it is not possible to use the existing brake switch. This required me to install a RoadMaster brake switch designed to fit the Jeep GC. I wired 12VDC from the toad battery and connected it to the new brake switch that when activates provides voltage through a prewired circuit in the motor home to a dash mounted LED. Thus when the brake petal is pushed by the air cylinder the switch closes and power illuminates the dash bulb which tells me the toad brake system is active.

The voltage to activate the toad’s brake, running and turn signal lights comes from the motor home light circuits. The diodes prevent the two power systems from colliding and causing electrical mayhem. Thousands of cars use this system successfully but that doesn’t mean my car and this system is not serving up a problem. It’s just that so far I can’t determine if these components are causing the problem.

What happens when the brake petal is pushed, the ignition is off and the car rolling? I do not know. Is this 2014 Jeep GC different from the previous 2010, 2011, 2012 and 2013 Jeep GCs? All of which use more or less the same toad braking systems installed while being towed that pushes the brake petal to activate the toad’s brake system. I spoke to a 2012 Jeep GC owner who uses a toad brake system and who has towed his Jeep all over the USA. So far he has never had a battery discharge problem over multiple towing days. So if my problem for the 2014 is that the new design uses more power then the previous Jeep GCs then maybe the charge line I added is the solution. Or when I fiddled with the four ground straps yesterday maybe I solved the problem. Only towing time is going to bring this problem to a conclusion. In the meantime, I am going to make sure I do not have a ground problem and evaluate if I can find a bulb kit that will fit the space so I can use independent bulbs.

Again, thanks for your input as it always gets me to thinking. <!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]-->
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Old 06-03-2013, 01:18 AM
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Re: Flat Towing Problem – Jeep Grand Cherokee 2014

Now my question is...I wonder if anything in the Jeep "powers up" in the background when it senses the vehicle rolling...

Sounds like your charging circuit helped... I just wonder if the ABS/wheel speed sensors turn a computer on...
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