2021 JLUR (manual, 3.6L ESS) Won't Start

[NBB]

Have to see a wiring diagram - and someone can correct me - but seems to me the two batteries have to be connected in some way. If so, then charging and checking voltage would be non-trivial unless completely removed or isolated from vehicle. I understand the smaller aux is basically there to keep the electronics powered during starting. That your uConnect is going blank during the attempted start seems like a clue to me. Maybe that aux battery is not in the condition you think it is in - maybe a few days of work killed it - permanently. My personal experience on CAN bus vehicles is that poking and prodding "wakes up" many individual pieces of the system, which will kill the battery in just a day or two. Charger may make you think it's good, but it really needs to be load tested while isolated - you're really looking at voltage from the larger battery. If it were me and I had no complete wiring diagram, I'd remove and test the battery, then put a scope directly on the terminals and look for voltage drop during start process.

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[demisx]

Following this thread I am measuring current parasitic drain. It's been drawing ~1A for the past 15 min. It seems pretty high. I'll give it another 15 min and start pulling out fuses hoping to isolate the offending circuit. Maybe these two issues are related.

EDIT: The voltage settled to ~70mA after about 30 mins.

 

[demisx]

Have to see a wiring diagram - and someone can correct me - but seems to me the two batteries have to be connected in some way. If so, then charging and checking voltage would be non-trivial unless completely removed or isolated from vehicle. I understand the smaller aux is basically there to keep the electronics powered during starting. That your uConnect is going blank during the attempted start seems like a clue to me. Maybe that aux battery is not in the condition you think it is in - maybe a few days of work killed it - permanently. My personal experience on CAN bus vehicles is that poking and prodding "wakes up" many individual pieces of the system, which will kill the battery in just a day or two. Charger may make you think it's good, but it really needs to be load tested while isolated - you're really looking at voltage from the larger battery.

This is a good point. I've tested the AUX battery in isolation and it gave ~12.6V reading. I will be receiving battery load tester today and will load test it in isolation with it later tonight.

If it were me and I had no complete wiring diagram, I'd remove and test the battery, then put a scope directly on the terminals and look for voltage drop during start process.

Should I do this test with both batteries connected or should I isolate a particular one? I am also going to try to start from the main battery once the parts arrive and I can make a fused N1->N2 jumper. Hopefully, Amazon's van is going to fit everything I've ordered for this "little" project.

 

[NBB]

Following this thread I am measuring current parasitic drain. It's been drawing ~1A for the past 15 min. It seems pretty high. I'll give it another 15 min and start pulling out fuses hoping to isolate the offending circuit. Maybe these two issues are related.

There are many devices that wake up and go back to sleep according to criteria you'll never find published specs for. IMO you'll pull your hair out chasing that. As noted in the other thread - given enough time everything goes back to sleep - maybe - you don't and won't know for sure. IMO, time is better spent chasing the likelihood your aux battery is now dead from a few days of computers and sensors waking up - isolate it from vehicle and load test.

EDIT - per your above post - the uConnect is your load test, IMO - does it normally go blank during start? I don't know, my Jeep hasn't arrived yet. If not, then definitely load test the aux battery. No - a "surface charge" of 12.6 or whatever with no load tells you nothing. You need wires right on the terminals and straight to a meter fast enough to see what could possibly be a very brief voltage drop causing uConnect to go into reset. I have to think if uConnect goes into reset, so does other parts of the system needed for starting.

Good luck..!

 

[demisx]

There are many devices that wake up and go back to sleep according to criteria you'll never find published specs for. IMO you'll pull your hair out chasing that. As noted in the other thread - given enough time everything goes back to sleep - maybe - you don't and won't know for sure. IMO, time is better spent chasing the likelihood your aux battery is now dead from a few days of computers and sensors waking up - isolate it from vehicle and load test.

Got it. As soon as I get this load tester. Hopefully, it's the right kind.

 

[ChattVol]

This is a good point. I've tested the AUX battery in isolation and it gave ~12.6V reading. I will be receiving battery load tester today and will load test it in isolation with it later tonight.



Should I do this test with both batteries connected or should I isolate a particular one? I am also going to try to start from the main battery once the parts arrive and I can make a fused N1->N2 jumper. Hopefully, Amazon's van is going to fit everything I've ordered for this "little" project.

Have you tried to jump start it with good 'ol fashion jumper cables?

 

[demisx]

Have you tried to jump start it with good 'ol fashion jumper cables?

No. My car is in such position right now that none of my jumper cables would reach. I guess this would be the next thing to order.

Also, as far as parasitic drain goes, it settled at 70mA after about 30 min, so I guess it's within normal. My next steps would be to load test the Aux battery once the tester arrives and try to start from main battery only (via N1->N2 jumper).

 

[ChattVol]

No. My car is in such position right now that none of my jumper cables would reach. I guess this would be the next thing to order.

Also, as far as parasitic drain goes, it settled at 70mA after about 30 min, so I guess it's within normal. My next steps would be to load test the Aux battery once the tester arrives and try to start from main battery only (via N1->N2 jumper).

I wouldn't overthink it. Put it in neutral, release the parking brake and push the jeep into a place you can try and jump start it.

 

[demisx]

EDIT - per your above post - the uConnect is your load test, IMO - does it normally go blank during start? I don't know, my Jeep hasn't arrived yet. If not, then definitely load test the aux battery. No - a "surface charge" of 12.6 or whatever with no load tells you nothing. You need wires right on the terminals and straight to a meter fast enough to see what could possibly be a very brief voltage drop causing uConnect to go into reset. I have to think if uConnect goes into reset, so does other parts of the system needed for starting.
Good luck..!

I don't remember if uConnect normally goes blank during start or not. Maybe one of the current JLUR owners can confirm. I've tried to start it off of the isolated AUX battery right now and I haven't noticed any voltage drop. It stayed around 12.3V-12.4V. Maybe my volt meter is not fast enough (Fluke 117). Don't know. Anyway, I'll load test both batteries once this tester arrives. Should be any minute now. But so far, I haven't seen any indication of a battery fault.

 

[demisx]

Both batteries have passed the test. At this point, I am pretty confident that they are both in good working condition. Gotta be something else.

 

[calemasters]

Lots of good information here. I am glad you are going to test both batteries with a load tester. I have seen many graveyard batteries that will read 12 volts on a DVOM with no load, but as soon as you put a load on the battery the voltage drops below 10 volts.

It would be interesting to see what happens if you replaced both batteries (even though they both test good) with "known good batteries". I have seen threads where this fixes a no start issue.

Good luck.

 

[NBB]

Did that thing come with a calibration sticker?

According to wire diagrams I see posted and procedures to remove aux battery - doesn’t seem to me you are actually testing aux battery. Aux battery is buried and has multiple wires connected to it. Without a 2021 factory wiring diagram confirmed to be for your vehicle - definitely NOT some well intentioned sketch - you have no means to confirm you are actually measuring anything about that aux battery until you physically remove all connections from the battery terminals on the actual battery - then test.

Again - the uConnect screen going blank - is this correct? If not, I 100% guarantee some part of your system is dropping way below 12v - like probably below 10v.

 

[maxmxa]

I agree with NBB. The Aux battery is buried in a box under main battery and you have to disconnect it to test. I've also heard people with bad Aux batteries that seemed to have normal voltage, but had to be replaced.

There is also possibility of a bad / loose ground somewhere if the battery, sensor and start button is not the problem. There was some recall last year on a ground jumper under the passenger side front wheel well near engine. It's kind of hard to find too, but should be on this forum. The recall had a picture of the location, but even with that it was hard to find.
Good luck

 

[NBB]

I tried to look up spec for that BT100 tester - how much power that tiny little toy looking thing can dissipate during its load test. I did not see a spec in the manual nor on manf site. I did find this note “Please note that this battery tester for car can't do load test and deep cycle.” - whatever that means in Chinglish. No offense here - just my experience having my time wasted with cheap tools. Consider removing that thing from the vehicle and going to a store with it to test - IMO you might be needing to go there anyway. Note many of their testers aren’t much better...

 

[SirMagnus89]

At this point, call your dealer, have them pick it up and fix it> no sense in doing any electrical damage when you do not need to. They will pick it up with a flat bed and give you a loaner.

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