TLDR: My stealership claims bad wheel speed sensors and/or damaged tone rings are causing a transmission issue I'm having. Is that even possible?

I have an 08 JK (i.e. the 42RLE trans) that started acting up recently. Every once in a while, when I would accelerate, it would get stuck in 2nd. I don't think this was limp mode, because I'd slow down and usually it would go into 1st. Or on some other times, I'd keep driving in 2nd, then it finally went into 3rd. Most of the time though, I'd need to turn my Jeep off/on to get back in action. Then it wouldn't happen again for a while. Another weird thing I noticed was that when cruising down the highway doing 70mph on flat ground with no wind at all, the torque converter would occasionally keep unlocking and locking causing the RPMs to fluctuate up and down a bit.

I checked trans fluid level, etc and didn't see anything obvious. Since I still have my lifetime powertrain warranty, I took it to my local stealership to get checked out (FWIW, I actually trust this one about as much as you could possibly trust a stealership). Long story short (I can elaborate if anyone cares), they told me this was caused by my wheel speed sensors and/or damaged tone rings. Since not part of the trans, that wasn't going to be covered under warranty. Needless to say, I took my Jeep home.

Does that make any sense to anyone? I know the trans has its own input and output speed sensors, so why would it care what the wheel speed sensors were reporting? Also, I've broken wheel speed sensors before and got the Christmas tree lit up on the dashboard ( ESP/BAS, ABS, and Traction Control lights on). Don't have that this time. Cruise control works fine too.

Anyways, I'm going to take a look at my Jeep this weekend. Just wondering if anyone had any thoughts about the wheel speed sensor/damaged tone ring theory before I started troubleshooting.

Thanks!

 

I know on the '12 and newer its absolutely possible. They do all kinds of dumb stuff if they don't see all the wheel sensors. I've been dealing with this on my 1-ton swap. I didn't think the '11 and down were as picky about it though.

 

Ok thanks - sounds like it's within the realm of possible then. I'm still curious what the trans needs the wheel speed info for...

Anybody know for sure about '07 - '11 JKs?

 

The auto trans does rely on the wheel speed sensors to choose what gear you need to be in. The 12+ is a little funny with changing gear ratio but you don't fall in to this category.

How much do they want to replace your wheel speed sensors and/ or a tone ring? I'm not usually one to allow the dealer to do the work but lifetime warranty would probably have influenced a few of my maintenance choices.

 

The 2012+ transmission needs wheel speed sensor data to determine output shaft speed. There is no direct sensor in the transmission for output shaft speed. That is why an axle gear ratio change without updating the computer can put the transmission into limp mode.

The 2007-2011 transmission has input and output shaft speed sensors. There is no mention in the service manual of the transmission needing wheel speed sensor data.

 

I didn't get a formal quote, but they said it was going to be on the order of few thousand bucks. They claimed 3 of the 4 wheels were to blame and that the tone rings themselves are not serviceable. So the ballpark quote they gave was to replace 3 wheel speed sensors, one of the front half axles, and the entire rear axle. They claimed none of that is covered under the lifetime powertrain warranty. So yeah...that's why I took my Jeep and went home.

 

This is great info - thanks!! If anyone has any thoughts on what might be causing my problem then, I'm all ears

I did have a couple trouble codes - P0721 and P1790, so i went ahead and replaced the output shaft speed sensor. Cleared codes, took it for a drive today, and that didn't fix it. In fact, it almost seems to be worse now. Basically got stuck in 2nd right away and feels more like limp mode. Nothing I could do would get it out. Turned if off/on, it started in 1st, but right after I just inched forward a bit, jumped right into 2nd (earlier than normal) and stuck there right away. So I limped back home and called it a day.

Haven't driven enough to get the check engine light back on yet. That's for tomorrow. Hopefully, it throws some different codes.

 

Here is some information for the P0721 code you posted. Notice the electrical circuit troubleshooting that needs to be done before the speed sensor is suspected.

P0721-OUTPUT SPEED SENSOR CIRCUIT PERFORMANCE
Theory of Operation
The transmission system uses two speed sensors, one to measure input rpm and one to measure output rpm. These inputs are essential for proper transmission operation. Therefore, the integrity of this data is verified through system checks.
When Monitored:
The transmission gear ratio is monitored continuously while the transmission is in gear.
Set Condition:
If there is an excessive change in the Output rpm in any gear.
Possible Causes
OUTPUT SPEED SIGNAL CIRCUIT OPEN
SENSOR GROUND CIRCUIT OPEN
OUTPUT SPEED SIGNAL CIRCUIT SHORT TO GROUND
OUTPUT SPEED SIGNAL CIRCUIT SHORT TO VOLTAGE
SENSOR GROUND CIRCUIT SHORT TO VOLTAGE
OUTPUT SPEED SENSOR
POWERTRAIN CONTROL MODULE

 

This would absolutely piss me off. "I'm having transmission troubles" which is part of the drive-train. We suspect speed sensors, not covered under warranty.

But wait? If the speed sensors impact and directly provide information to ensure proper drive train operation and impact the performance of the transmission, why aren't they part of the drive-train warranty? What if I waited until the poor performance due to the speed sensors destroyed the trans, would anything be covered then? or would it be determined that the cause of trans failure was due to speed sensors and I'm on my own?

I missed my 5 year inspection and no longer have the life-time power train warranty due to that. Stories like this, make me realize I'm not missing anything since they would still find a way to screw me.

What a joke. I don't believe I'll ever purchase another FCA vehicle even though I love my JK. Then they scratch their heads, "I wonder why our new vehicle sales keep declining compared to all the other OEMs...we must need to add keyless entry, heated seats and Apple CarPlay Radios". It could never be about sticking behind your product and honoring your warranties when folks actually need to use it.

What was the estimated cost of repair the dealership provided? I'ld be tempted to have them do the repair. If it fixes the problem, then great. If not, then go after the power-train warranty, and then make sure they refund you your money for their initial non fix repair.

 

Ryan, take special note that nothing in the possible causes (in Ron's post copied below) points to the wheel speed sensors. It's so simple to read a code and look it up, if they can't even do that right...