2009 6.7 Cummins auto 6 speed randomly downshifts

[09megacabcummins]

i have a 2009 megacab 4x4 with the 6.7l cummins and I am having issues where it keeps downshifting into 5th then 4th and sticks in 4th for a while then will go back to normal, been having it happen about once a day then it won’t do it again till the next day, it’s nothing i can replicate myself it’s just when it feels like it, sometimes in the morning and others in the evening. Thanks in advance for any help.

 

[Fast69Mopar]

Is the check engine light on? Have you had a scan tool connected to see if there are any 1-trip failures? A quick look at the CVI's would also give an idea about clutch integrity.

How many miles are on the truck?

What is the condition of the transmission fluid and filters?

Has the trans ever been out of the truck for an overhaul?

Do you have a programmer installed?

 

[MADDOG]

In addition to ^^^those^^^ questions I'd ask:

1. Are you in full auto or Tow/Haul mode?
2. Does the transmission do this when you are a low road speeds in Full Auto?
3. Do the symptoms appear when the transmission is still warming up?

 

[09megacabcummins]

The truck has 225,000 miles on it, i do have two codes one is p0716 and the other is P0700. I have had the truck since 170,000 miles its full auto when it happens and does it in tow haul mode as well, when the transmission is acting up it wont allow me to use the manual shifter on the gear selector. I have not had a shop look at it yet because i’m very busy, its my work truck. Also when it does give me problems its only in 5th and 6th gear so low speeds are fine and the symptoms show randomly this morning it happened about 5 miles from home. Have no idea on condition of fluid or filters possible filter may be clogged but i’m no transmission guy. No tuner all stock and transmission has never been out of truck as far as I know.

 

[mtnrider]

P0700 is "Transmission Control System Malfunction". The brains that control the transmission basically. I would get it diagnosed before you start randomly throwing money at it.


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[09megacabcummins]

Haven’t had issues for over week and today it started again. It rained today so possibly water getting into something, gonna try to take truck to trans shop tomorrow and see what they find

 

[09megacabcummins]

So far so good a local transmission shop replaced speed sensors in the transmission because they weren’t sending any information to the computer

 

[09megacabcummins]

Problems returned after speed sensor replacement i took it back again and they told me it had no codes on the transmission and they couldn’t get it to do it and said i should pretty much just drive it until it threw a code which it threw a code about 4 days later and i took the truck back again and they were able to replicate it then and replaced the speed sensor plug because it wouldn’t lock on good and not even a half mile from leaving the transmission shop it started acting up again so i took it back and they are going to try to replace the wiring harness because the speed sensor is loosing communication at some point

 

[09megacabcummins]

It’s been fixed for quite a while and it was the plugs for the speed sensors on the transmission computer thanks for the help