[Tyler-98-W68]

Some people have had their PTU replaced and have noticed a difference in AWD operation post PTU replacement. My 2014 Cherokee had a PTU and RDM replacement less than 1 week after it was purchased new. Ever since the replacement there has always been a noticeable amount of wheel spin prior to AWD activation when using Auto mode. Before the replacement there was no wheel spin and the transfer of power was seamless with no front wheel slippage before the rear tires got power. When I purchased my 2016 I immediately noticed that it had zero front wheel slippage in auto mode on slippery surfaces. Driving my 2014 after my 2016 was quite frustrating as the 2014 really didn’t seem to be working as advertised. I theorized that after a PTU replacement Jeep changed the programming to prevent future drivetrain damage. Fast forward a few years and I had a PTU replacement in my 2016 however its AWD operation after the replacement did not change and worked as it did when new.

Using Alfa OBD I’ve been able to subject both my 2014 and 2016 to the same scenarios and data log to see the differences in the AWD operation and there are quite a few differences. I’m not sure I understand all the differences, but I’ll do my best to explain them.

I’ll refer back to this video of my 2016 Cherokee driving around in Auto Mode

The operation of my 2016 is what I would consider “normal” AWD system activates when slowing down and coming to a stop, upon starting again the rear torque value immediately climbs even with a small amount of throttle input (throttle input in % at the bottom of the video)
Now watch this video of my 2014

You can see the AWD system send power to the rear when slowing down and coming to a stop, however watch carefully as I accelerate from a stop at 1:52 you can see the rear torque value staying at 60nm but not moving up to a much higher number like in my 2016, You can see shortly after I get up to speed the value goes to 0 indicating that the vehicle is now operating in FWD mode (This shifting to FWD mode is the same as my 2016 as considered “normal)
At 2:22 I slow down and go around a corner, you can see again that the value of 60nm shows up as the awd system again is activated but as I accelerate that value stays at 60nm and then goes to 0 again as I get up to speed.
Now refer back to my 2016 Video at 4:37 where I slow down and turn a corner and accelerate you can see the rear torque value go much higher even though I’m using the same amount of throttle input. It looks like while the AWD system is active on the 2014 at low speed and when accelerating it doesn’t send hardly any power to the rear possibly explaining why there is a bunch of wheel spin on slick surfaces.
I can recreate this scenario over and over with the 2014. It appears that the system defaults to FWD mode even quicker and more often than my 2016 but when it is in the AWD mode its really not sending any meaningful torque to the rear wheels. A lot of throttle input does activate the AWD system and sends torque the “normal” way. You can see an example of this at 4:35 in the 2014 video. If you watch the 2014 video more you can see it showing values of 60,72,48,84 very small values when the AWD system is active but its not the same as the 2016 where the 2016 values raise immediately.
So there is a difference in the AWD system and its measurable, here is some more information and differences between the 2014 and 2016.

Here is the AWD system status for my 2014 when operating in 2WD mode

Operating in AWD mode

When in 4-low

Now my 2016 Cherokee Operating in 2WD Mode

Operating in AWD Mode

When in 4-low


You will notice some differences right away all in the Actuator position status
The 2016 has all the expected values for operating in 2WD mode, the 2014 has some really odd values
The actuator position status is different in every value, and in 1 value it even shows 4LO, not sure if its relevant to the difference of the AWD operation but its interesting none the less. The one value that in slightly interesting is the RDM Range Fork Position as being “BetweenHandN” I do see that on my 2016 but only DURING a shift in to low range. As see here

Now my 2014 Shifting in to low range

Here is my 2016 shifting through the selec terrain modes while driving

Here is my 2014 Shifting through the selec terrain modes while driving

I can’t really explain why there are such differences in the operation between the 2 vehicles but there is a difference in how the AWD system activates on the 2014 and it is measurable. I’m going to try and have a chat with my dealership and see if they can provide any additional information, although I’m doubtful they will give me anything. I’ll need to do some more research to see how/why everything is so different between the 2 vehicles.

 

[Ronin38]

There certainly appears to be some hinkyness going on with the '14.

 

[Tyler-98-W68]

Now to add some more confusion to the mix. When I pull the PTU fuse on my 2016 for fuel economy reasons, as outlined here

Here is what is displayed



The PTU Range Fork Position shows the same value as the 2014 does but again not a clue what it all means.

 

[Tyler-98-W68]

A slight update over a year later, the AWD performance has been steadily declining and to the point where now Auto, Snow and Sport mode don't really activate the rear wheels hardly at all.
I decided to do some logging with AlfaOBD and see what power was actually being sent to the rear wheels, but before we get to that here is the test condition.

Auto mode ESP full off, Sport mode didn't do anything and neither did snow mode, could only get moving with Sand/Mud Mode
Here is sand/mud mode.

The last time I tested everything out I figured it was the PTU being the issue and it still may be the issue however I then thought maybe the PTU is working fine and the RDM is the issue. I put a camera under the vehicle pointed at the driveshaft coming out of the PTU and wanted to see if in fact the driveshaft was spinning. If it was then the issue would be the TTD (torque transfer device in the rear drive module) if the PTU wasn't spinning then maybe it was a PTU issue.

I jacked the front wheels up so they were off the ground and put the vehicle in drive in auto mode. Video is below

As you can see the driveshaft is spinning so the problem appears to be something in the RDM.

With the front wheel in the air I loaded up alfaOBD to see what kind of power was being send to the rear wheels in each one of the selec terrain modes.

Auto Mode


In auto mode the wheels spin freely and there is only 84nm of torque send to the rear wheels (which is basically nothing) vehicle just sat there and spun the front wheels back end did nothing

Snow Mode


This was a bit more interesting, there was a bit more torque send 252nm (185ft/lbs)
The front wheels did not spin and the rear wheels were getting power (and were on the ground) so since the back wheels weren't spinning and the RDM was getting power the fronts wouldn't spin either, great there is a difference from auto mode but still not enough power to do anything with.

Sport Mode


Sport mode is even more interesting because while it shows sending the same amount of power as snow mode(252nm 185ft/lbs), the front tires would turn around ever so slightly, even though the back tires were getting power just like in snow mode, no real explanation for this other than the AWD system is messed up.

Sand/Mud Mode


Sand/Mud sends even more power 504nm (371ft/lbs) and it's noticeable the front tires don't spin and the vehicle wants to jump forward off the jack stands, basically this is the only mode that provides any type of useful power to the rear wheels.

There has to be some programming in the DTCM that has changed the behavior of the AWD system, prior to the PTU and RDM replacement 7 years ago now, it worked fine. Subsequent to that it's never worked right. I've scanned the PTU module and RDM module and they have no faults so it would appear everything is "working" right. One thing to note the vehicle shifts into 4x4 low and that works 100% as it should.

At this point i'm thinking about remapping the TCM so that what used to be sand/mud mode will now shift like it does ni Auto mode. Totally a bandaid fix but it's something that I can do. I suppose I could go to the dealer and see if there is newer DTCM software but that is about it.

 

[sqenixs]

A slight update over a year later, the AWD performance has been steadily declining and to the point where now Auto, Snow and Sport mode don't really activate the rear wheels hardly at all.
I decided to do some logging with AlfaOBD and see what power was actually being sent to the rear wheels, but before we get to that here is the test condition.

Auto mode ESP full off, Sport mode didn't do anything and neither did snow mode, could only get moving with Sand/Mud Mode
Here is sand/mud mode.

The last time I tested everything out I figured it was the PTU being the issue and it still may be the issue however I then thought maybe the PTU is working fine and the RDM is the issue. I put a camera under the vehicle pointed at the driveshaft coming out of the PTU and wanted to see if in fact the driveshaft was spinning. If it was then the issue would be the TTD (torque transfer device in the rear drive module) if the PTU wasn't spinning then maybe it was a PTU issue.

I jacked the front wheels up so they were off the ground and put the vehicle in drive in auto mode. Video is below

As you can see the driveshaft is spinning so the problem appears to be something in the RDM.

With the front wheel in the air I loaded up alfaOBD to see what kind of power was being send to the rear wheels in each one of the selec terrain modes.

Auto Mode


In auto mode the wheels spin freely and there is only 84nm of torque send to the rear wheels (which is basically nothing) vehicle just sat there and spun the front wheels back end did nothing

Snow Mode


This was a bit more interesting, there was a bit more torque send 252nm (185ft/lbs)
The front wheels did not spin and the rear wheels were getting power (and were on the ground) so since the back wheels weren't spinning and the RDM was getting power the fronts wouldn't spin either, great there is a difference from auto mode but still not enough power to do anything with.

Sport Mode


Sport mode is even more interesting because while it shows sending the same amount of power as snow mode(252nm 185ft/lbs), the front tires would turn around ever so slightly, even though the back tires were getting power just like in snow mode, no real explanation for this other than the AWD system is messed up.

Sand/Mud Mode


Sand/Mud sends even more power 504nm (371ft/lbs) and it's noticeable the front tires don't spin and the vehicle wants to jump forward off the jack stands, basically this is the only mode that provides any type of useful power to the rear wheels.

There has to be some programming in the DTCM that has changed the behavior of the AWD system, prior to the PTU and RDM replacement 7 years ago now, it worked fine. Subsequent to that it's never worked right. I've scanned the PTU module and RDM module and they have no faults so it would appear everything is "working" right. One thing to note the vehicle shifts into 4x4 low and that works 100% as it should.

At this point i'm thinking about remapping the TCM so that what used to be sand/mud mode will now shift like it does ni Auto mode. Totally a bandaid fix but it's something that I can do. I suppose I could go to the dealer and see if there is newer DTCM software but that is about it.

That is concerning, I wonder if this is something that all cherokees deal with. The AWD system slowly becomes useless as the car gets up in mileage. Either on purpose or due to wear-related issues. Reminds me of the apple iphone battery wear fiasco that ended in a huge warranty replacement of peoples batteries and a change to the OS.

 

[Tyler-98-W68]

I'm pretty sure it's strictly a programming related issue, my 2016 never had this issue and my 2021 also does not do this either, 4-low works just fine as does sand/mud mode, after watching PTU power transfer in AlfaOBD over the last few days its obvious its a programming issue, also the PTU range positions (in the first post) are totally different between my 2016 and the 2014 so I think the dealer may be able to do a DTCM reflash and hopefully fix the issue.

 

[Shoulder]

A slight update over a year later, the AWD performance has been steadily declining and to the point where now Auto, Snow and Sport mode don't really activate the rear wheels hardly at all.
I decided to do some logging with AlfaOBD and see what power was actually being sent to the rear wheels, but before we get to that here is the test condition.

Auto mode ESP full off, Sport mode didn't do anything and neither did snow mode, could only get moving with Sand/Mud Mode
Here is sand/mud mode.

The last time I tested everything out I figured it was the PTU being the issue and it still may be the issue however I then thought maybe the PTU is working fine and the RDM is the issue. I put a camera under the vehicle pointed at the driveshaft coming out of the PTU and wanted to see if in fact the driveshaft was spinning. If it was then the issue would be the TTD (torque transfer device in the rear drive module) if the PTU wasn't spinning then maybe it was a PTU issue.

I jacked the front wheels up so they were off the ground and put the vehicle in drive in auto mode. Video is below

As you can see the driveshaft is spinning so the problem appears to be something in the RDM.

With the front wheel in the air I loaded up alfaOBD to see what kind of power was being send to the rear wheels in each one of the selec terrain modes.

Auto Mode


In auto mode the wheels spin freely and there is only 84nm of torque send to the rear wheels (which is basically nothing) vehicle just sat there and spun the front wheels back end did nothing

Snow Mode


This was a bit more interesting, there was a bit more torque send 252nm (185ft/lbs)
The front wheels did not spin and the rear wheels were getting power (and were on the ground) so since the back wheels weren't spinning and the RDM was getting power the fronts wouldn't spin either, great there is a difference from auto mode but still not enough power to do anything with.

Sport Mode


Sport mode is even more interesting because while it shows sending the same amount of power as snow mode(252nm 185ft/lbs), the front tires would turn around ever so slightly, even though the back tires were getting power just like in snow mode, no real explanation for this other than the AWD system is messed up.

Sand/Mud Mode


Sand/Mud sends even more power 504nm (371ft/lbs) and it's noticeable the front tires don't spin and the vehicle wants to jump forward off the jack stands, basically this is the only mode that provides any type of useful power to the rear wheels.

There has to be some programming in the DTCM that has changed the behavior of the AWD system, prior to the PTU and RDM replacement 7 years ago now, it worked fine. Subsequent to that it's never worked right. I've scanned the PTU module and RDM module and they have no faults so it would appear everything is "working" right. One thing to note the vehicle shifts into 4x4 low and that works 100% as it should.

At this point i'm thinking about remapping the TCM so that what used to be sand/mud mode will now shift like it does ni Auto mode. Totally a bandaid fix but it's something that I can do. I suppose I could go to the dealer and see if there is newer DTCM software but that is about it.

Very interesting information.

One question I do have is did you get the latest V69 transmission recall done recently? If so, is it possible the new programming changed how the 4WD system operates even though it wouldn't make a whole lot of sense to begin with?

 

[Tyler-98-W68]

Very interesting information.

One question I do have is did you get the latest V69 transmission recall done recently? If so, is it possible the new programming changed how the 4WD system operates even though it wouldn't make a whole lot of sense to begin with?

Super good observation, the answer is yes I got the V69 recall done, I'll have to check and see when because I made a post about it because it definitely helped out the transmission and made it shift better. Looks like I had it done last February, it was winter time then so if there was any adverse AWD system changes I should have noticed it by now.

 

[Shoulder]

Super good observation, the answer is yes I got the V69 recall done, I'll have to check and see when because I made a post about it because it definitely helped out the transmission and made it shift better. Looks like I had it done last February, it was winter time then so if there was any adverse AWD system changes I should have noticed it by now.

Good to know. I did a quick search, and it looks like the V69 recall started in Summer of 2019, which was after your initial post to this thread, and like you said, you got it done back in February (I got mine done around Summer of last year). It wouldn't surprise me if Jeep decided that in order to preserve some of the longevity of the 4WD system, they decided to alter the programming in the process. It is possible the spline issue is caused by additional wear on the system due to the 4WD system, and by cutting power more often, it preserves it longer. Of course, this is pure speculation.

On a broadly similar vain, when MINI came out with the Countryman ALL4, there were initial issues with clutches burning up fast. It was determined that the additional load required to drive all 4 wheels burned out the clutch for the transmission faster, and thus required a more durable one via a recall if I remember correctly.

 

[Tyler-98-W68]

This issue was prevalent before (which is when I made the original post (pre V69) it just seems to have gotten worse, so maybe it is V69 related.

 

[Shoulder]

This issue was prevalent before (which is when I made the original post (pre V69) it just seems to have gotten worse, so maybe it is V69 related.

The plot thickens!