Complex electrical issue solved

[Medictrode]

Long Thread alert!

First, some back story. I, as well as many others have a JL that would freak out so much, it would sometimes render the vehicle useless. In some cases, you'd be driving and lose power steering as every light flashes on the dash, Tach and speedo go away and other oddities happen. Other times, the Jeep wouldn't start, and if it did you'd not be able to shift it into gear because again, every damned light would start flashing. Sometimes pulling the negative battery cable(and the AUX GND Wire) then reconnecting would fix the issue, sometimes it would not.

Reading codes was pointless because there would be 70+, and most of them had to do with the various modules losing CAN BUS and not being able to talk to each other. Mine started while it was under warranty, so I took it to the dealer with doubts of any success. This is due to most guys being simple parts changers with zero troubleshooting skill, and the fact that they really don't get paid to fix issues that aren't in their time allotment schemes. Needless to say I was right, they didn't figure it out after wasting 3 months at various dealers, and most simply changing random parts.

So I figured it was time to use my skills and get dirty with this thing. First, of course is searching around. Many people whom have had this issue had their dealers say it was the AUX battery(hint for later) and they replace that, the main batt or both and send it on it's way. Well, as you read these poor peoples posts, shortly thereafter their Jeeps start doing the same thing.. Hmmm

My AUX battery was indeed weak, but I knew deep down in my skillset that it wasn't directly related to the issues. I ended up doing the Bypass mod(Jumper) which connects both batteries together. This didn't solve the issue, but I did notice my charging system with that AUX Battery connected going upwards of 14.8-14.9 volts. If I disconnected the AUX Batt completely, the voltage would drop to normal charging levels. This makes sense as the extra load on the Alternator caused it to crank output a bit..Again, more clues for later..

So the parts changers at the dealer somehow concluded that a front wiring harness was to blame, then it was a whole new front sway bar disconnect that "Should fix the issue". Ok, more clues for my wasted time.

My next steps was to research what is all on the High Speed CAN BUS line, and every affected system like the power steering and shifter control were on same, but so was the front sway bar disconnect for some idiotic reason. At this point, it was time to hook some CAN sniffing tools to said network, as well as my oscilloscope then start data logging when I did my normal driving. What I found was a complete failure of this network. Like asystole for a split second, which the other modules didn't like, hence the freak out.

Ok, cool more clues. However, CAN BUS is such a crappy network to use in vehicles due to the fact that as stated above, one thing brings it down, the entire network goes down, and also that fact that you can't unplug certain items, like power steering or the vehicle won't let you drive. This makes troubleshooting super difficult.

What I did find interesting was when I unplugged the front sway bar disconnect, things operated perfectly except the sway bar warning light. All data was transmitted uninterrupted as well. But didn't I say the parts changers replaced said sway bar module and disconnect ? I certainly did, but I ripped into the module and found a damaged voltage regulator which has a threshold voltage input of around 15-16 volts.

So this got me thinking.... And I could be wrong.... But as stated earlier, the voltage output of the charging system would go to ~15V to try and make of for that idiotic non necessary AUX battery for the stupid stop/start system. If this happens, it likely was the cause of this voltage regulator going bad both in the old module, and the new one. When this happens, it would bring the entire CAN BUS down and brick the vehicle.

The current fix was to either unplug the sway bar, but I actually use the Jeep and a off road vehicle, so I've added 2 330 Ohm resistors in line with each leg of the CAN Line going to the STAR connector behind the glove box. This "cushions" the CAN BUS signal so it doesn't bring down the entire system, and I can still use the sway bar. My next step is to re design the sway bar circuit so it has a proper voltage regulator.

I hope this helps some people as I feel your frustrations with these pointless dealers and the Narcan eaters they employ(moslty, not all). I also cannot guarantee this is your issue on your particular Jeep, but it's more information than I could find already out on the internet. Thank you for reading...

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[Flip]

Long Thread alert!

First, some back story. I, as well as many others have a JL that would freak out so much, it would sometimes render the vehicle useless. In some cases, you'd be driving and lose power steering as every light flashes on the dash, Tach and speedo go away and other oddities happen. Other times, the Jeep wouldn't start, and if it did you'd not be able to shift it into gear because again, every damned light would start flashing. Sometimes pulling the negative battery cable(and the AUX GND Wire) then reconnecting would fix the issue, sometimes it would not.

Reading codes was pointless because there would be 70+, and most of them had to do with the various modules losing CAN BUS and not being able to talk to each other. Mine started while it was under warranty, so I took it to the dealer with doubts of any success. This is due to most guys being simple parts changers with zero troubleshooting skill, and the fact that they really don't get paid to fix issues that aren't in their time allotment schemes. Needless to say I was right, they didn't figure it out after wasting 3 months at various dealers, and most simply changing random parts.

So I figured it was time to use my skills and get dirty with this thing. First, of course is searching around. Many people whom have had this issue had their dealers say it was the AUX battery(hint for later) and they replace that, the main batt or both and send it on it's way. Well, as you read these poor peoples posts, shortly thereafter their Jeeps start doing the same thing.. Hmmm

My AUX battery was indeed weak, but I knew deep down in my skillset that it wasn't directly related to the issues. I ended up doing the Bypass mod(Jumper) which connects both batteries together. This didn't solve the issue, but I did notice my charging system with that AUX Battery connected going upwards of 14.8-14.9 volts. If I disconnected the AUX Batt completely, the voltage would drop to normal charging levels. This makes sense as the extra load on the Alternator caused it to crank output a bit..Again, more clues for later..

So the parts changers at the dealer somehow concluded that a front wiring harness was to blame, then it was a whole new front sway bar disconnect that "Should fix the issue". Ok, more clues for my wasted time.

My next steps was to research what is all on the High Speed CAN BUS line, and every affected system like the power steering and shifter control were on same, but so was the front sway bar disconnect for some idiotic reason. At this point, it was time to hook some CAN sniffing tools to said network, as well as my oscilloscope then start data logging when I did my normal driving. What I found was a complete failure of this network. Like asystole for a split second, which the other modules didn't like, hence the freak out.

Ok, cool more clues. However, CAN BUS is such a crappy network to use in vehicles due to the fact that as stated above, one thing brings it down, the entire network goes down, and also that fact that you can't unplug certain items, like power steering or the vehicle won't let you drive. This makes troubleshooting super difficult.

What I did find interesting was when I unplugged the front sway bar disconnect, things operated perfectly except the sway bar warning light. All data was transmitted uninterrupted as well. But didn't I say the parts changers replaced said sway bar module and disconnect ? I certainly did, but I ripped into the module and found a damaged voltage regulator which has a threshold voltage input of around 15-16 volts.

So this got me thinking.... And I could be wrong.... But as stated earlier, the voltage output of the charging system would go to ~15V to try and make of for that idiotic non necessary AUX battery for the stupid stop/start system. If this happens, it likely was the cause of this voltage regulator going bad both in the old module, and the new one. When this happens, it would bring the entire CAN BUS down and brick the vehicle.

The current fix was to either unplug the sway bar, but I actually use the Jeep and a off road vehicle, so I've added 2 330 Ohm resistors in line with each leg of the CAN Line going to the STAR connector behind the glove box. This "cushions" the CAN BUS signal so it doesn't bring down the entire system, and I can still use the sway bar. My next step is to re design the sway bar circuit so it has a proper voltage regulator.

I hope this helps some people as I feel your frustrations with these pointless dealers and the Narcan eaters they employ(moslty, not all). I also cannot guarantee this is your issue on your particular Jeep, but it's more information than I could find already out on the internet. Thank you for reading...

Thank you for sharing your dilemma, experience, and resolution! You found and fixed the problem yourself without the help of the useless dealerships. Great job ?

 

[Bob Burd]

Funny, one of the reasons to use CANBUS is to allow all these modules to tap onto the same pair of twisted wires to save routing 17 (or whatever) extra pairs of wires. Yet Jeep simply routes them all to same two passive junction boxes behind the glove box. If they replaced those boxes with an active controller, debugging these issues would be WAY easier, and your jeep far safer, too. I disconnected my sway bar at the box two years ago for what could be the same problem. Props for digging way deeper than I could.

 

[DonH63]

I have read for years about the requirement to add resistors for bus isolation. But automakers will do anything to save a penny (or less) when it is multiplied over millions of vehicles. Many years ago I read an article about the up and coming CANBUS and how it needed some serious HW and protocol standards work before being ready for prime time, but it was implemented pretty much as-is back then. That said, I do not follow it, and perhaps the recommendation made it into the standard but was not required for compliance certification? Wouldn't be the first time engineering was sacrificed for money.

 

[Als@Ohio]

Long Thread alert!

First, some back story. I, as well as many others have a JL that would freak out so much, it would sometimes render the vehicle useless. In some cases, you'd be driving and lose power steering as every light flashes on the dash, Tach and speedo go away and other oddities happen. Other times, the Jeep wouldn't start, and if it did you'd not be able to shift it into gear because again, every damned light would start flashing. Sometimes pulling the negative battery cable(and the AUX GND Wire) then reconnecting would fix the issue, sometimes it would not.

Reading codes was pointless because there would be 70+, and most of them had to do with the various modules losing CAN BUS and not being able to talk to each other. Mine started while it was under warranty, so I took it to the dealer with doubts of any success. This is due to most guys being simple parts changers with zero troubleshooting skill, and the fact that they really don't get paid to fix issues that aren't in their time allotment schemes. Needless to say I was right, they didn't figure it out after wasting 3 months at various dealers, and most simply changing random parts.

So I figured it was time to use my skills and get dirty with this thing. First, of course is searching around. Many people whom have had this issue had their dealers say it was the AUX battery(hint for later) and they replace that, the main batt or both and send it on it's way. Well, as you read these poor peoples posts, shortly thereafter their Jeeps start doing the same thing.. Hmmm

My AUX battery was indeed weak, but I knew deep down in my skillset that it wasn't directly related to the issues. I ended up doing the Bypass mod(Jumper) which connects both batteries together. This didn't solve the issue, but I did notice my charging system with that AUX Battery connected going upwards of 14.8-14.9 volts. If I disconnected the AUX Batt completely, the voltage would drop to normal charging levels. This makes sense as the extra load on the Alternator caused it to crank output a bit..Again, more clues for later..

So the parts changers at the dealer somehow concluded that a front wiring harness was to blame, then it was a whole new front sway bar disconnect that "Should fix the issue". Ok, more clues for my wasted time.

My next steps was to research what is all on the High Speed CAN BUS line, and every affected system like the power steering and shifter control were on same, but so was the front sway bar disconnect for some idiotic reason. At this point, it was time to hook some CAN sniffing tools to said network, as well as my oscilloscope then start data logging when I did my normal driving. What I found was a complete failure of this network. Like asystole for a split second, which the other modules didn't like, hence the freak out.

Ok, cool more clues. However, CAN BUS is such a crappy network to use in vehicles due to the fact that as stated above, one thing brings it down, the entire network goes down, and also that fact that you can't unplug certain items, like power steering or the vehicle won't let you drive. This makes troubleshooting super difficult.

What I did find interesting was when I unplugged the front sway bar disconnect, things operated perfectly except the sway bar warning light. All data was transmitted uninterrupted as well. But didn't I say the parts changers replaced said sway bar module and disconnect ? I certainly did, but I ripped into the module and found a damaged voltage regulator which has a threshold voltage input of around 15-16 volts.

So this got me thinking.... And I could be wrong.... But as stated earlier, the voltage output of the charging system would go to ~15V to try and make of for that idiotic non necessary AUX battery for the stupid stop/start system. If this happens, it likely was the cause of this voltage regulator going bad both in the old module, and the new one. When this happens, it would bring the entire CAN BUS down and brick the vehicle.

The current fix was to either unplug the sway bar, but I actually use the Jeep and a off road vehicle, so I've added 2 330 Ohm resistors in line with each leg of the CAN Line going to the STAR connector behind the glove box. This "cushions" the CAN BUS signal so it doesn't bring down the entire system, and I can still use the sway bar. My next step is to re design the sway bar circuit so it has a proper voltage regulator.

I hope this helps some people as I feel your frustrations with these pointless dealers and the Narcan eaters they employ(moslty, not all). I also cannot guarantee this is your issue on your particular Jeep, but it's more information than I could find already out on the internet. Thank you for reading...

Good read, long but good. Same issue a friend had on his Dodge truck. It would freak, every dash light flashing. If I remember correctly the dealership replaced the steering rack twice! It would be fine for less than one day then freak out again. Dodge through in the towel and said unrepairable and did a buyback. I give you a lot of credit for finding the issue and fixing it. You must really love that jeep.??

 

[storyg]

Medictrode,
Excellent troubleshooting and result. Regarding the 330 ohm resistors, what is the minimum wattage rating needed? I suspect the current draw is fairly low. Perhaps with aging of the circuit, the current draw could increase slightly. I should think upsizing the minimum resistor wattage by say, 30% won't take up any appreciable space with never a worry about the circuit and the resistors-addition from failing at all.

I image you may encase the resistors and leads against dirt/water/other once you are certain the results are final. I am thinking a close-fitting plastic tube over the resistor, plus an inch or two longer at each end of soldered (?) connections (room allowing) to help with vibration or movement over time, plus heat shrink over the plastic tube-ends but maybe I am over thinking that.

Gene

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