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Discussion Starter #1
Just got back from a trip to Colorado with my new 2012 Rubicon Unlimited with auto trans. This is the first of my five Wranglers that I was comfortable enough in to drive long distances rather than trailering it. Now on to the problems.

I was going up Tin Cup Pass outside of Buena Vista, CO with the Jeep in 4Lo and trans in third gear. This is not a difficult road but is quite bumpy. After one mile I pulled over to the side to let a car past going the other way. This was an escort and had no business being on a bumpy road like this but you see everything on the Forest Service Roads in Colorado. I slipped the Jeep into neutral waiting for him to pass and when he was gone I dropped it back into gear to keep going and had nothing from the trans, it just reved. I checked to make sure the transfer case had not jumped to neutral and all was fine. The shifter would not allow any changes from what was indicated on the dash as third gear. When you moved the shifter from side to side there was no change. I tried 2hi and had a little creeping forward movement while the trans was still stuck in 3rd. I did have reverse so I turned around and headed down hill. Back in 4lo I now had full use of third gear so I crept the one mile down the hill to St. Elmo.

Now I had full use of third gear in 4lo or 2hi. The shifter was completely unresponsive and would not change gears in the drive position but did have reverse. When in 2hi taking off in third gear was as you can imagine a slow excelleration. I tried turning the engine off again as I had when the trouble first started and this time all went back to normal. The next 980 miles home in 2hi were uneventful.

I did have the presence of mind to record absolutely all of this on my iphone in video. Three weeks from now I will be heading back to Colorado going deep in the woods hunting for ten days. 80 miles into the forest with no cell phone reception and most likely snow on the ground is no time to lose a transmission, you can't walk out from that at my age. Now watch the dealer simply say they can't duplicate the problem.

Cruise control also quits from time to time while on the interstate and I got an indicated 186.3 miles per gallon on the trip home. Real math said a good bit less.:nonono:
 

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Sounds more like a computer control issue than a hardware (tranny) failure. The "re-boot" of when you turned off the engine and restarted and things were normal is what makes me say that. Or, am I missing something in your description?
 

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Discussion Starter #3
Computer is what I was thinking too but it did not reset it the first time I shut it off, only the second. I can't get my mind around what a computer tells the trans. to not allow any movement while mechanically in forward gear but to go ahead and allow reverse. There could not have been a heat issue as it was 40 degrees and I had only gone a mile, heat could have put it in some sort of limp mode and possibly allowed only third gear but that still does not explain zero movement when it all began, seemed like it was in neutral but was stuck in third and 4lo.

I just absolutely fear them saying they reflashed it and go enjoy the woods! I am in a new Jeep vs. an old one so I don't get stuck in the woods miles from nowhere. There are real dangers being many miles in the cold away from civilization, a Jeep trans/computer does not need to be one of them.
 

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Computer is what I was thinking too but it did not reset it the first time I shut it off, only the second. I can't get my mind around what a computer tells the trans. to not allow any movement while mechanically in forward gear but to go ahead and allow reverse. There could not have been a heat issue as it was 40 degrees and I had only gone a mile, heat could have put it in some sort of limp mode and possibly allowed only third gear but that still does not explain zero movement when it all began, seemed like it was in neutral but was stuck in third and 4lo.

I just absolutely fear them saying they reflashed it and go enjoy the woods! I am in a new Jeep vs. an old one so I don't get stuck in the woods miles from nowhere. There are real dangers being many miles in the cold away from civilization, a Jeep trans/computer does not need to be one of them.

Well, sometimes it takes a minute or so to clear buffers, so maybe it wasn't off for long enough the first time, if our theory is correct? It sounds like a bug to me, and I would ask my dealer to escalate to the regional service manager for Jeep, so that they know it has happened. If it happened to you, it will (or has) happened to others, and if it is software, then that kind of fix is much easier and cheaper for them to create and deploy than hardware. Hell, I bought a new BMW motorcycle in 2004 and its brain got a couple of new flashes inside of 2 years, and each was an improvement so...
 

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If that happened to me, I would have disconnected the negative terminal of the battery, for 5 or 10 minutes, to "re-set" the computer.

That may or may not have worked, but it is definitely worth a try.

Be sure to carry the correct size wrench with you (a complete tool kit is better) to do this when you are in the woods.

Mabar
 

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If that happened to me, I would have disconnected the negative terminal of the battery, for 5 or 10 minutes, to "re-set" the computer.

That may or may not have worked, but it is definitely worth a try.

Be sure to carry the correct size wrench with you (a complete tool kit is better) to do this when you are in the woods.

Mabar
I agree. What I also don't understand is when the OP did get it to move from a stop if the transmission is in "3" it should still start in "1" and shift up to "3", not start in "3" lugging the engine. I have a feeling this has something to do with the +/- which is a electrical switch IIRC, and is causing others issue with downshifting by the slightest touch, something it shouldn't be doing. It could be a tranny problem too, I'm not so sure about a reflash. JMO
 

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Discussion Starter #7
I agree. What I also don't understand is when the OP did get it to move from a stop if the transmission is in "3" it should still start in "1" and shift up to "3", not start in "3" lugging the engine. I have a feeling this has something to do with the +/- which is a electrical switch IIRC, and is causing others issue with downshifting by the slightest touch, something it shouldn't be doing. It could be a tranny problem too, I'm not so sure about a reflash. JMO
Yes, it was stuck in third gear when in both 2hi and 4low. This makes it rev and excellerate slowly. I think the computer had the shifter locked out electrically. There are several electrical gremlins with this Jeep now including the cruise control and the fuel use computer.
 

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Yes, it was stuck in third gear when in both 2hi and 4low. This makes it rev and excellerate slowly. I think the computer had the shifter locked out electrically. There are several electrical gremlins with this Jeep now including the cruise control and the fuel use computer.
Sounds like your tranny went into 'limp-home' mode for some reason. Hopefully you will have some codes stored to help dealer figure out why. It shouldn't have been overheating with that huge trans cooler on the 2012s, unless your failure to move forward while in gear and reving was due to a fault in the torque converter causing it to not lock up. Slipping torque converter is a big cause of heat in tranny. IIRC
 

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Yes, it was stuck in third gear when in both 2hi and 4low. This makes it rev and excellerate slowly. I think the computer had the shifter locked out electrically. There are several electrical gremlins with this Jeep now including the cruise control and the fuel use computer.
Now it sounds like you lost a sensor that tells the brain how fast you are going. All those faults are in systems that have to know how fast your wheels are turning.
 

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If that happened to me, I would have disconnected the negative terminal of the battery, for 5 or 10 minutes, to "re-set" the computer.

That may or may not have worked, but it is definitely worth a try.

Be sure to carry the correct size wrench with you (a complete tool kit is better) to do this when you are in the woods.

Mabar
On everything sold in the USA since 96 you also need to turn on the headlights or hazard flashers to reset the PCM. Part of the OBDII requirements are that the computer have a power reserve to prevent the loss of data in the event of a power loss. To achieve that they put capacitors in there to store enough energy to keep the memory alive for quite some time. The capacitors are easily discharged by turning something on that has power available with the key off.

Sounds like your tranny went into 'limp-home' mode for some reason. Hopefully you will have some codes stored to help dealer figure out why. It shouldn't have been overheating with that huge trans cooler on the 2012s, unless your failure to move forward while in gear and reving was due to a fault in the torque converter causing it to not lock up. Slipping torque converter is a big cause of heat in tranny. IIRC
Limp mode is dead on. It saw a problem and threw a fit. Your drive home may have caused the codes to be erased, but they may still be stored. I don't know what kind of drive cycle protocol is used in these.
 

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On everything sold in the USA since 96 you also need to turn on the headlights or hazard flashers to reset the PCM. Part of the OBDII requirements are that the computer have a power reserve to prevent the loss of data in the event of a power loss. To achieve that they put capacitors in there to store enough energy to keep the memory alive for quite some time. The capacitors are easily discharged by turning something on that has power available with the key off.



Limp mode is dead on. It saw a problem and threw a fit. Your drive home may have caused the codes to be erased, but they may still be stored. I don't know what kind of drive cycle protocol is used in these.
You brought a slightly off-topic question to mind. In some past Jeep models, especially my 2002 GC, you could display stored codes by cycling the ignition key from off to run three times. Codes were displayed in odo.

Anybody know if there is a way to do this in JKs other than an OBD code reader?
 

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You brought a slightly off-topic question to mind. In some past Jeep models, especially my 2002 GC, you could display stored codes by cycling the ignition key from off to run three times. Codes were displayed in odo.

Anybody know if there is a way to do this in JKs other than an OBD code reader?
That's a good question. I know on my truck you can do it by holding the trip reset button in as you turn the key to run. It won't give the whole story, but it's something.
 

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That's a good question. I know on my truck you can do it by holding the trip reset button in as you turn the key to run. It won't give the whole story, but it's something.
These are always 'undocumented' tricks, probably discovered by accident or leaked by automotive engineer types. Most of the 'tuners' also read OBD codes, it seems, and I'll get one eventually, but, in the mean time, what the heck is wrong with owners being able to read the codes?
 

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These are always 'undocumented' tricks, probably discovered by accident or leaked by automotive engineer types. Most of the 'tuners' also read OBD codes, it seems, and I'll get one eventually, but, in the mean time, what the heck is wrong with owners being able to read the codes?
Many of them are documented in the service manual. I suspect that techs use them and start telling their friends. On some Cadillacs the secret handshake is the only way you can get the codes.
 

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Quadratec says:
To check your JK Codes, use this sequence on your ignition. Insert key and turn the ignition On-Off-On-Off then back to the On position and then notice the codes given in the odometer read-out.
https://www.quadratec.com/jeep_knowledgebase/article-139.htm

Of course, JK ignitions are off-acc-on-start, so??

Yeap, it works! Three quick cycles; off-acc-on and back to off (before dash lights go on.) Has to be quick cycles back off or it doesn't work. I have no codes stored so I just get "---------" in odo display.


So, OP, read your codes and let us know....
 

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Just curious as to why you would choose to head up-hill on 3rd gear, while on 4L. If a car was able to go past you... if seems the Jeep would've made it just fine on 2H. Also, I don't think the 4L is meant for sustained speeds in excess of 30mph.

The manual also says shifting to 4L is easiest while in motion in a straight line... at a speed <5MPH. This helps the gears fall into place.
 

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Sounds to me like a hard fault, is there a CEL on, there should be? If not maybe the computer is shot.:confused:
 

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Just curious as to why you would choose to head up-hill on 3rd gear, while on 4L. If a car was able to go past you... if seems the Jeep would've made it just fine on 2H. Also, I don't think the 4L is meant for sustained speeds in excess of 30mph.

The manual also says shifting to 4L is easiest while in motion in a straight line... at a speed <5MPH. This helps the gears fall into place.
Depends on how "low" a low gear you want for the hill, and road conditions.

Assuming a 3.73 axle ratio, WA580, 5-speed auto transmission, and a Sport or Sahara 2.72 transfer case ratio:

2HIGH or 4HIGH in 1st gear = 13.39 crawl ratio (1st gear is 3.59 ratio)

4LOW in 3rd gear = 14.31 crawl ratio (3rd gear is 1.41 ratio)

These 2 gear combinations are for all practical purposes, the same crawl ratio.

Craw ratio = transmission gear ratio x axle ratio x transfer case ratio

I personally prefer to be in 4LOW while off-roading, since my off-roading is generally much slower speed driving. 4LOW gives you more torque/power at the wheels at any given road speed, a much slower road speed, and it is easier on the engine and transmission.

Generally, you should never exceed 20 or 25 mph in 4LOW.

Mabar
 

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Depends on how "low" a low gear you want for the hill, and road conditions.

Assuming a 3.73 axle ratio, WA580, 5-speed auto transmission, and a Sport or Sahara 2.72 transfer case ratio:

2HIGH or 4HIGH in 1st gear = 13.39 crawl ratio (1st gear is 3.59 ratio)

4LOW in 3rd gear = 14.31 crawl ratio (3rd gear is 1.41 ratio)

These 2 gear combinations are for all practical purposes, the same crawl ratio.

Craw ratio = transmission gear ratio x axle ratio x transfer case ratio

I personally prefer to be in 4LOW while off-roading, since my off-roading is generally much slower speed driving. 4LOW gives you more torque/power at the wheels at any given road speed, a much slower road speed, and it is easier on the engine and transmission.

Generally, you should never exceed 20 or 25 mph in 4LOW.

Mabar
Agreed... althought I prefer being on 2H or 4H until I know I may need 4L. That's just personal perferenace I suppose.

OP said a car made up the hill with no issues... If so, I can't imagine a stock Wrangler, regardless of trim, needing anything other than 2H. Am I missing something?
 

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Up Hill Bill said:
Quadratec says: https://www.quadratec.com/jeep_knowledgebase/article-139.htm

Of course, JK ignitions are off-acc-on-start, so??

Yeap, it works! Three quick cycles; off-acc-on and back to off (before dash lights go on.) Has to be quick cycles back off or it doesn't work. I have no codes stored so I just get "---------" in odo display.
I'm thinking we need a sticky on this! :thumb:
 
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