M1123 did not shift in last gear

[frauhansen]

Good evening together

My 4 speed currently does not seem to shift into 4th gear or overdrive.
Drove in the snow a week ago and on the way home felt like "I'm missing a gear"!
I had manually shifted to "2" or "1" while driving, since very mountainous, to brake more evenly downhill with all four. Better than the overbraking rear overtakes me.
Maybe something has frozen, so my guess. TV cable, If it has that, in suspicion.
Today briefly made on tour and the problem persists even at warmer temperatures.

The truck just does not shift into last gear. High speed and maximum 50mph. On the tour of 50mi in pouring rain he had shifted short times back to usual mode. This about 3 times and not for long. Maybe 1mi until he changed his mind again and fell into the speed madness.

I tried to check if the torque converter lock is still open, but seems to be closed. I also shifted the automatic selector lever back and forth several times. No change. Admittedly, also no change to D with OD and D without OD.

Any ideas enyone to help me out

thx,
hansen

 

[Mogman]

Do you have a 700R4 transmission? if not you do not have a TV cable.
If you have a 4L80 it sometimes helps to power cycle the TCM but see if you have any codes first.

 

[frauhansen]

hmmm... its a 1123 from '98. How to identify whitch gearbox is installed?
power cycle the TCM... let me check what this is.

 

[SmartDrug]

hmmm... its a 1123 from '98. How to identify whitch gearbox is installed?
power cycle the TCM... let me check what this is.

Unless someone retrofitted a 700r4, you have the 4L80E in the M1123.

 

[Mogman]

You have a 4L80
You power cycle the TCM by disconnecting the batteries, but do not do that until you read how to get the codes off of the TCM, this should help.
You do not want to erase the codes before you read them.

 

[frauhansen]

The curse and blessing of self-healing problems.
Today I brought the truck from home to my workshop. This time in dry weather and spring-like 48 °F.
Just like before... it won't come out of second gear. Turns almost to death.
But, ohh miracle, abder half of the distance the problem has settled. It just shifted right up and stayed that way. Even after the restart after refueling.
Problem has cured itself.

I can only imagine that I got with snow and rain somewhere water in what does not belong there.
Is unsatisfactory since I am now not able to name a clear cause. And therefore also do not know when and if this occurs again.
Does this ring a bell with anyone? Any usual suspect?

 

[Mogman]

Have you checked to see if there are codes from the TCM?
You need to learn how to do it so if there are not any stored codes you can get them on the fly when your transmission is not working properly, that will be the best way to figure out where your problem is. otherwise you are just peeing in the wind.
It sounds like your transmission is going into limp mode, there should be codes when this is happening and it may still have them stored

 

[frauhansen]

No I had no more probert. I had assumed that only active codes are displayed. That is also saved I was not aware. My failure!
Then I'll read out the days times and post here.

 

[Mogman]

It is normal for the transmission to not go into torque converter lock until the transmission comes up to temperature. this will seem like it is not shifting into high but much different than being stuck in 2nd.
If it is stuck in limp mode it will not shift at all when in drive, it will start out in second gear and stay there, if you are keenly aware of your HMMWV normal operation you will notice that is is a little boggy when taking off from a stop as it is in second not first.
But pulling codes and being able to pull codes when it is acting up is your best course to find the issues.

 

[Mogman]

I do not know if the 4L80 TCM stores codes that are no longer active, most of the later stuff does, in fact I did not think the 4L80 got a dedicated TCM until the mid 2000s (2005?) so the HMMWV may actually be using a modified PCM (powertrain control module) as that is what controlled the transmission circa 1991 when it was released.

 

[frauhansen]

That's right... now that you mention it... Driving from a stop was very doughy. And I'm not sure I noticed a gear shift either.

Now the question remains why... I will see the days if and how I get error codes from the system.
And in parallel times from the manual which you had linked to me above the electrical components search whether what is stripped and thus exposed to water.

 

[Elijah95]

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