42RLE Overdrive Mode Flakiness

[bkeith72]

Hi friends, I have been experiencing some strange flakiness with the O/D functionality on my 2004 LJ - hoping someone here might have an idea for me. The problem I'm experiencing is with the functionality of my O/D switch. When I am driving around town I will press the O/D switch, the light turns on and the Jeep will shift from 4 - 3 as expected.

As I am driving around town, the Jeep will randomly decide that 4th gear is an option to use again. Sometimes just while cruising down the road. Sometimes I notice after a stop light that the Jeep goes through all the gears, all the way to 4th - even while the O/D light is still on.

At this point, while cruising I will press the O/D switch again, the Jeep shifts back to 3rd but, the light is now off. It will run in 3rd with the O/D light off sometimes but usually it will shift back to 4th after a few moments.

Then I the O/D switch again, again the Jeep shifts back to 3rd and this time the O/D light is lit. Usually it will stay in 3rd with the light lit until I stop again at a stop sign, red light or just randomly and I'll realize that the Jeep is again in 4th with the O/D light lit. Then I repeat the cycle. I end up pressing the O/D switch quite often as you can imagine. Sometimes 15-20 times during a short trip around town to keep it in 3rd.

Appreciate any advice or thoughts about why the Jeep is forgetting the state of the OD switch and shifting the Jeep into 4th when the OD light is on ... regularly.

 

[LONGJP2]

Appreciate any advice or thoughts

Try cycling power to the PCM and see if the problem goes away.
It might only be temporary, but doesn't cost anything.
After that, I would try a new switch.

 

[Jerry Bransford]

You might just be feeling the torque converter locking up instead of it really going into 4th/Overdrive. The engine rpms will drop some when the torque converter locks but you'd still be in third gear when the Overdrive is disabled.

 

[AjRagno]

You’re probably just feeling the torque converter lock and unlock.

With overdrive off the torque converter locks up in 3rd gear. With overdrive on the torque converter locks up in 4th gear. You need to consider if 3rd gear with the torque converter locked or 4th gear and torque converter unlocked is best for the conditions and hit the switch accordingly. If you turn overdrive off before the 2-3 up shift, it’s guaranteed that torque converter will lock up when you hit 3rd gear.

 

[bkeith72]

For those who are pre re-gear (like me), what is the best to engage the OD mode? While still in park or after movement is already underway.

When I am out tomorrow I will take note of how much the RPMs rise when pressing the OD switch and report back. Hoping that would help determine if this a torque convertor lock/unlock or something else.

Thanks all

 

[bkeith72]

It was the Throttle Position Sensor

In hindsight I suppose this makes sense if the computer is getting an incorrect reading from the TPS then the RPMs and gear could be managed incorrectly for the given speed and actual throttle position.

Anyway - if you ever have a similar behavior with your Jeep, consider replacing your TPS. Thanks all for your tips and ideas on how to remediate.

Problem solved