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sprinkles08, ASE Certified Technician
Category: Transmissions
Satisfied Customers: 23100
Experience:  Chrysler/Dodge/Jeep master tech ASE Master and Advanced Certified, Chrysler/Dodge/Jeep Master Certified, Trans Specialist
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I have a 2008 2500 6.7 with a 68RE transmission. It has 201k

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I have a 2008 2500 6.7 with a 68RE transmission. It has 201k on it. It get a po 721 and a u010 code.i know they are for differ things but I want to address the po 721 code. I have changed the output senser and its plug. And the code keeps reappearing. I took it to a Diesel shop and they down loaded a updated soft wear that address that problem. The transmission with shift great when first started up and may shift ok if I take it out on a drive. But some times it will down shift into 4th and stay there until I let off the throttle and pick it back up again. It might happen again or not. Sometimes I have to pull over and turn the truck off and start it back up and will work fine the rest of my drive (about an hour) I also feel the OD kick in and out. Driving at 70 mph it's tacting around 1800 rpm the it jumps up to 2000 rpm and come back down to 1800. How do I determine whether it a transmission problem or the TCM acting up?

Hello and welcome to JustAnswer!

This code sets when the trans controller sees an implausible change in transmission output speed. If the sensor has been ruled out then this is going to be a wiring issue between the sensor and TCM. There is an intermittent open circuit due to a break somewhere and the signal is coming and going while driving. Either the problem could be located and repaired or a new wire could be ran.

I hope that helps! My goal is your satisfaction today. If you feel I've been professional and helpful, your 5-star rating at this time is most appreciated. However, if you still need my help you can reply back here and I'll respond as soon as possible! Thank you!

Customer: replied 27 days ago.
I checked out the wiring to the TCM and found it sound and ok. But in the process I discovered the sensor wire went to a multi wire pin connector. I checked for which pin was being used for the sensor and cleaned and adjusted the pin so it should make a better connection. I also put some Dielectric grease on the pins to aid in making the connection. I drove it on a 30 mile trip and the po721 code didn't return.


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