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Discussion Starter #1
I've got a very strange shifting issue on my 2015 JKU. I'll be cruising down the highway at highway speeds and all of a sudden the trans will down shift to 4th and never shift back to 5th. The only way to get back into 5th is the manually shift to 5th. If I shift out of manual mode the trans will go back to 4th and stay there. At that point if I kick the accelerator the trans will go down to 3rd and be stuck there. So I have to shift back into manual mode to get the engine revs down. Here's the weird part, it only happens on the highway at highway speeds. It doesn't happen in local traffic. In local traffic it shifts as it should. This only happens at cruising speeds on the highway. I've had times in in rush hour traffic where speeds slow down, the trans seems to reset itself and shifts normally again until it gets back to cruising speed. After about 5 minutes of cruising speed it'll downshift again to 4th and be stuck there. I took it to the dealer and they couldn't replicate the issue I even made a video of it but they weren't interested.

After living with this for a while here's what I've narrowed it down to.

Possible speed sensor issue
I haven't been able to pinpoint a speed that triggers it. It'll happen anywhere between sustained 50 -70 mph. The truck is not throwing any codes. The only thing it'll do occasionally is to throw the ABS and traction control light but it'll go off within minutes and not result in a code.

Engine coolant temp, trans fluid temp, outside heat and humidity

Trans temp is between 167 to 172. Higher or lower trans temps don't seem to matter. Coolant temps don't seem to matter either. Intake air temp doesn't seem to matter, but may be part of it.

Outside ambient outside temperature seems to be the culprit. I'm in the mid Atlantic and we've had a very wet and warm fall. Once the outside temperatures cooled down I have been able to make a correlation to ambient temperature and the shifting issues. When the outside temperature is above 68 degrees it'll downshift to 4th and get stuck there, 68 and below trans shifts fine at highway speeds. Below 68 degrees the issue does not occur.

I'm guessing it's a sensor but I'm not sure which one or ones I should be looking at. I'm hoping someone may have an idea which sensors I need to look at. Thanks for taking the time for reading this overly long post!!!
 

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I would do a full code scan first (some codes do not set lights).. If your scan tool does have the ability to monitor “mode 6” data, you can many times find sensors that are faulting periodically but not enough to hit the threshold for setting a dash light or setting a trouble code.

You may also want to disconnect the negative cable from the battery for 30 minutes and hook a jumper wire between both positive and negative cables (while negative is off the battery of course) to drain any parasitic charge in the system. Often times the transmission control unit (TCU) will have to reload basic shift strategy and then relearn your driving style.
 

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might be a crankshaft position sensor issue... that sensor is near a catalytic converter. Its cheap and easy to replace. Try that first. Might also need a trany fluid flush. If its over 80k miles I would get that done aswell.
 

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I've got a very strange shifting issue on my 2015 JKU. I'll be cruising down the highway at highway speeds and all of a sudden the trans will down shift to 4th and never shift back to 5th. The only way to get back into 5th is the manually shift to 5th. If I shift out of manual mode the trans will go back to 4th and stay there. At that point if I kick the accelerator the trans will go down to 3rd and be stuck there. So I have to shift back into manual mode to get the engine revs down. Here's the weird part, it only happens on the highway at highway speeds. It doesn't happen in local traffic. In local traffic it shifts as it should. This only happens at cruising speeds on the highway. I've had times in in rush hour traffic where speeds slow down, the trans seems to reset itself and shifts normally again until it gets back to cruising speed. After about 5 minutes of cruising speed it'll downshift again to 4th and be stuck there. I took it to the dealer and they couldn't replicate the issue I even made a video of it but they weren't interested.

After living with this for a while here's what I've narrowed it down to.

Possible speed sensor issue
I haven't been able to pinpoint a speed that triggers it. It'll happen anywhere between sustained 50 -70 mph. The truck is not throwing any codes. The only thing it'll do occasionally is to throw the ABS and traction control light but it'll go off within minutes and not result in a code.

Engine coolant temp, trans fluid temp, outside heat and humidity

Trans temp is between 167 to 172. Higher or lower trans temps don't seem to matter. Coolant temps don't seem to matter either. Intake air temp doesn't seem to matter, but may be part of it.

Outside ambient outside temperature seems to be the culprit. I'm in the mid Atlantic and we've had a very wet and warm fall. Once the outside temperatures cooled down I have been able to make a correlation to ambient temperature and the shifting issues. When the outside temperature is above 68 degrees it'll downshift to 4th and get stuck there, 68 and below trans shifts fine at highway speeds. Below 68 degrees the issue does not occur.

I'm guessing it's a sensor but I'm not sure which one or ones I should be looking at. I'm hoping someone may have an idea which sensors I need to look at. Thanks for taking the time for reading this overly long post!!!
Hi billybobjku,
I understand why this would be concerning. Please feel free to send us a private message if you would like to continue pursuing this with your dealer or if you would like to get a second opinion. We would be happy to assist in getting this concern addressed.
Lydia
Jeep Social Care Specialist
 

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Discussion Starter #5
Hi billybobjku,
I understand why this would be concerning. Please feel free to send us a private message if you would like to continue pursuing this with your dealer or if you would like to get a second opinion. We would be happy to assist in getting this concern addressed.
Lydia
Jeep Social Care Specialist
Thanks so much I'll be in touch!
 

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Have you tried a code reader that can read transmission codes? Not all code readers can read transmission codes.
 

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Discussion Starter #8
I would do a full code scan first (some codes do not set lights).. If your scan tool does have the ability to monitor “mode 6” data, you can many times find sensors that are faulting periodically but not enough to hit the threshold for setting a dash light or setting a trouble code.

You may also want to disconnect the negative cable from the battery for 30 minutes and hook a jumper wire between both positive and negative cables (while negative is off the battery of course) to drain any parasitic charge in the system. Often times the transmission control unit (TCU) will have to reload basic shift strategy and then relearn your driving style.
Thanks Randy!
I've had the codes read at the dealer still nothing shows up. They did reset the trans module and that didn't help. Since it's been cooler here the issue hasn't happened until it warmed up a bit yesterday. I was on the highway trans sticks in 4th gear, the outside temp was 71, speed was 67, revs were 3070, coolant temp was 208, trans was 167, IAT was 93. Coming home using the same route and speed the outside ambient temp was 65 no shifting issues. Kinda wish I noted the coolant, trans and IAT temps on the way back.
 

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No codes makes it tougher, you'll need someone that can actually trouble shoot a transmission. It could be a solenoid, something with the valve body, or a multitude of other issues. I'm thinking a transmission solenoid. Keep us posted.
 

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Thanks Randy!
I've had the codes read at the dealer still nothing shows up. They did reset the trans module and that didn't help. Since it's been cooler here the issue hasn't happened until it warmed up a bit yesterday. I was on the highway trans sticks in 4th gear, the outside temp was 71, speed was 67, revs were 3070, coolant temp was 208, trans was 167, IAT was 93. Coming home using the same route and speed the outside ambient temp was 65 no shifting issues. Kinda wish I noted the coolant, trans and IAT temps on the way back.
That can be a real bugger...
As noted by another poster on this thread, it may be a lagging or sticky solenoid. Manually shifting the transmission uses the same circuitry as the TCU doing the shifting. Only difference is that the TCU may have shifted the solenoid and then you gave the solenoid a second bump by shifting it manually...
But...
When the solenoids are shifted, constant power is kept on that solenoid...

Via the OBDII port and scan tool, you can read out the current gear that the TCU (or you manually) have selected. If you can connect a code reader that displays this - you would then know if the TCU has selected 5th gear, but the solenoid never completed the shift.

Mode 6 data is what I would go after at this point. You can isolate every sensor on the vehicle along with the solenoids. Your dealer or a pretty tech savvy shop can do this.

How many miles are on this unit and are you still under warranty?
 

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Discussion Starter #11
That can be a real bugger...
As noted by another poster on this thread, it may be a lagging or sticky solenoid. Manually shifting the transmission uses the same circuitry as the TCU doing the shifting. Only difference is that the TCU may have shifted the solenoid and then you gave the solenoid a second bump by shifting it manually...
But...
When the solenoids are shifted, constant power is kept on that solenoid...

Via the OBDII port and scan tool, you can read out the current gear that the TCU (or you manually) have selected. If you can connect a code reader that displays this - you would then know if the TCU has selected 5th gear, but the solenoid never completed the shift.

Mode 6 data is what I would go after at this point. You can isolate every sensor on the vehicle along with the solenoids. Your dealer or a pretty tech savvy shop can do this.

How many miles are on this unit and are you still under warranty?
When the problem started it was 97000 over 100K now. Its been documented at the dealer they said they would honor the warranty if they could replicate the issue but who knows. So far every time I've taken it in they've said couldn't replicate it. Being that the issue is tough to replicate I think I may have to do the scan trouble shooting myself.

Something interesting yesterday however. To recap, at highway speeds, when the issue occurs and it gets stuck in 4th I'll manually shift to 5th. If I shift out of manual mode it'll go right back to 4th. It wont start shifting normally again on it's own until traffic slows enough for it to get a few shifts in at slower speeds. At that point it'll shift perfectly at highway speeds until it pickups whatever errant signal that triggers the downshift to 4th and the process starts all over again.

Yesterday it was warm again, the truck was stuck in 4th going highway speed. I manually shifted to 5th, turned on the cruise control. With the cruise control still on I shifted out of manual mode, the truck stayed in 5th, I turned off the cruise control, the truck stayed in 5th. No issues for the rest of the ride home. This is the first time I've been able to get it out 4th at highway speeds. If that will work consistently that's the best workaround I've found so far.
 

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Billybob, What gear/tire combo are you running? It is possible that the transmission is shifting exactly as programmed but is behaving this way due to a change in tire height or gear ratio. If your tire height and gearing are stock ignore this reply. If they are not you might want to consider TCM programming modifications.
 

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Discussion Starter #13
Billybob, What gear/tire combo are you running? It is possible that the transmission is shifting exactly as programmed but is behaving this way due to a change in tire height or gear ratio. If your tire height and gearing are stock ignore this reply. If they are not you might want to consider TCM programming modifications.
You bring up a great point as when it happens it does feel like I've got my old gears back, but I've been running a 3.5 lift, 35s and 4.56 gears for a number of years now with no shifting problems at all. This is a recent issue. This issue just started in August, right after I had the dealer change the filter and flushed the trans, but yeah when the issue happens it does feel like it did before I re-geared. I've got a trail dash 2 with an unlocked pcm I've tried different tunes but the issue still occurs in every tune I've tried. So it has to be some signal from somewhere that triggers the tcm to downshift. That signal only occurs at ambient temps of over 68 and only at highway cruising speeds. Pretty crazy. I'd be happy to talk to you about tcm programming if you think it may help. Let me know what you think.
 

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Unless the tunes you have tried include TCM tuning then it is unlikely that they will have any impact on the transmission shifting. I suspect that when you took your Jeep to the dealer that they followed standard procedure and plugged a Witeck 2.0 module into your OBDII port, it indicated that there was a TCM flash/update available and they flashed that into your Jeep (along with any other module updates that were recommended). At that point the new TCM programming may have impacted your shift schedule. Even if you go to the dealer to have your floor mats changed they will follow this process. We also utilize Witech at our shop and it is a great tool. Plug it into the vehicle and everything about that vehicle pops up on the laptop on our workbench wirelessly. All the codes that have ever been in the vehicle, service bulletins, modules that need flashed, access to any previous service etc.

When you vehicle downshifts to 4th are any of the following changing?
- Throttle pedal position
- Vehicle speed (mph) - even slightly
- Engine RPM
- Engine load

If the answer is yes to any of these I would bet that a TCM tune would correct your issue. If you want to purchase a TCM outright from us just go to the link in my previous post. If you can afford your Jeep being down for a few days you can pull your TCM and ship it to us for a reflash for less $$ - which is also an option in the link above.
 

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Discussion Starter #17
Unless the tunes you have tried include TCM tuning then it is unlikely that they will have any impact on the transmission shifting. I suspect that when you took your Jeep to the dealer that they followed standard procedure and plugged a Witeck 2.0 module into your OBDII port, it indicated that there was a TCM flash/update available and they flashed that into your Jeep (along with any other module updates that were recommended). At that point the new TCM programming may have impacted your shift schedule. Even if you go to the dealer to have your floor mats changed they will follow this process. We also utilize Witech at our shop and it is a great tool. Plug it into the vehicle and everything about that vehicle pops up on the laptop on our workbench wirelessly. All the codes that have ever been in the vehicle, service bulletins, modules that need flashed, access to any previous service etc.

When you vehicle downshifts to 4th are any of the following changing?
- Throttle pedal position
- Vehicle speed (mph) - even slightly
- Engine RPM
- Engine load

If the answer is yes to any of these I would bet that a TCM tune would correct your issue. If you want to purchase a TCM outright from us just go to the link in my previous post. If you can afford your Jeep being down for a few days you can pull your TCM and ship it to us for a reflash for less $$ - which is also an option in the link above.
Hey Mike I took a look at the invoice from the dealer and yeah you're right they did reprogram the TCM.

When the issue happens the RPMs fly up, throttle was at 24% not sure if that moved though. I don't know about engine load but I can tell from a butt dyno perspective once the issue happens and I manually shift to 5th it does feel like it's lugging in 5th. It doesn't feel like that when the truck is shifting normally. It's still pretty strange that this issue only happens in warmer weather only at highway speeds. It's like the TCM is getting something from a sensor that triggers the downshift. However I never had the problem until that TCM was reprogrammed. Maybe a bug in the programming? What's the over under on bug vs temp sensitive sensor? LOL

I'll give you a call tomorrow thanks for getting back to me!
 

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I have similar problem. My transmission gets stuck in 3rd no matter what you do to it. Seems to happen after things have warmed up. In manual mode, I cannot get the transmission to shift up from 3rd when it is misbehaving. if i pull off to the side of the road, things seem to settle down for just a few minutes. It behaves as if the vacuum system loses its vacuum. The malfunction seems to happen most when I am on a long climb at high altitude...loss of vacuum due to heavy throttle and perhaps an undersized electric vacuum backup pump installed by Jeep for such a problem. the manual shift mode also acts like a bad switch on the manual upshift side of the mechanism. Local dealer has not been helpful and has caused more problems than I started with...reluctant to go back. if there is a Jeep Rep on line here, please respond. thanks.
 

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I have similar problem. My transmission gets stuck in 3rd no matter what you do to it. Seems to happen after things have warmed up. In manual mode, I cannot get the transmission to shift up from 3rd when it is misbehaving. if i pull off to the side of the road, things seem to settle down for just a few minutes. It behaves as if the vacuum system loses its vacuum. The malfunction seems to happen most when I am on a long climb at high altitude...loss of vacuum due to heavy throttle and perhaps an undersized electric vacuum backup pump installed by Jeep for such a problem. the manual shift mode also acts like a bad switch on the manual upshift side of the mechanism. Local dealer has not been helpful and has caused more problems than I started with...reluctant to go back. if there is a Jeep Rep on line here, please respond. thanks.
If your trans is actually stuck in 3rd and will not shift regardless of throttle position, engine speed or vehicle speed - even after coming to a stop then you have a different issue than the one listed above. If your trans goes to 3rd and stays there this is most likely a "limp home" default and can be caused by various problems. Your dealer or a shop like us that has a Witech module or a good Snap-on or other scan tool should be able to locate the cause. Many times it is an "incorrect X gear ratio" error indicating possible internal transmission issues. There are many other causes for the trans limp mode but I would start with a good scan tool.
 
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