M1123 transmission

[Mogman]

If you look at this you will see the trans light wires come out of the same harness (see the loop around the wires that the arrows are pointing to, that is a harness sheath) as the brake switch, the TPS, and the ESS break out of.
The ESS and the TPS go into sheaths of there own but not the brake switch and MIL light (at least that is what it shows) so if you find the right spot on the harness you should see two sets of sheathed wires and 4 individual wires, two of which are going to the brake switch and the other two go to the MIL.

EDIT, if you follow the small harness back from the TPS it should take you right to that spot.

 

[Mogman]

Common sense dictates the place all those wires break out of the harness should be around the rear of the left valve cover, but sometimes common sense plays no part in the building of the HMMWV

 

[kingConan]

If you look at this you will see the trans light wires come out of the same harness (see the loop around the wires that the arrows are pointing to, that is a harness sheath) as the brake switch, the TPS, and the ESS break out of.
The ESS and the TPS go into sheaths of there own but not the brake switch and MIL light (at least that is what it shows) so if you find the right spot on the harness you should see two sets of sheathed wires and 4 individual wires, two of which are going to the brake switch and the other two go to the MIL.
View attachment 908319
EDIT, if you follow the small harness back from the TPS it should take you right to that spot.

Thank you, I have gone through the diagram, and still no connector. Checked all connections on the transmission and everything is tight and in order. Checked the TCM and no corrosion or water anywhere. Checked the batteries and all wires. Everything appears in good working order. I did not use a volt meter but did a visual and physical inspection. On a whim I ran it up to operational temp and checked the transmission fluid. It's reddish pink but has what looks like shiny graphite in it. No actual metal shavings, but just a fine shine. It does not feel gritty or anything. Is this a bad thing or normal? Transmission was serviced when it was out of the truck for the new engine back in March of this year. I've put about a thousand miles on it since then. I genuinely appreciate all of the help.

 

[Mogman]

Follow the wires from the TPS, (throttle position sensor) on the right side of the injection pump, it should lead you to where it goes into a larger harness, that is where the wires for the MIL lamp should be.

I have no idea about what you are seeing, might be clutch material might be nothing

One way or another you need to get the codes ESPECIALLY if your transmission is not operating normally, a working trans light is crucial for anyone with a 4L80E, I just don't know what else to say.

 

[Mogman]

It is possible whomever removed the light cut the wires, maybe even flush where they came out of the harness.
At this point I would be looking for where the individual TPS and ESS harnesses and the brake switch wires come out of the larger harness for cut wires.

 

[DREDnot]

Post a pic of the pigtail end of your new trans light.
I just looked under my M1123 and my trans light has two wires going into this single (polarized) plug.
Best I can tell it goes forward into the harness with the arrow.

 

[kingConan]

Follow the wires from the TPS, (throttle position sensor) on the right side of the injection pump, it should lead you to where it goes into a larger harness, that is where the wires for the MIL lamp should be.

I have no idea about what you are seeing, might be clutch material might be nothing

One way or another you need to get the codes ESPECIALLY if your transmission is not operating normally, a working trans light is crucial for anyone with a 4L80E, I just don't know what else to say.

I found the transmission light wiring. The original one had been broken and tucked into the frame and hidden. New light is installed and working. Tomorrow is trying to pull codes.

 

[kingConan]

I found the transmission light wiring. The original one had been broken and tucked into the frame and hidden. New light is installed and working. Tomorrow is trying to pull codes.

Also, went through the connections at the solenoids, cleaned and added dielectric grease. Was going to add a seafome additive to the transmission fluid to see if that helps. Has anyone used this? I was thinking add that, drive it fifty miles then change the fluid. Any ideas?

 

[Mogman]

Good deal, I am curious is the light lit with the engine running?

 

[kingConan]

Good deal, I am curious is the light lit with the engine running?

No, only on the glow plug cycle.

 

[kingConan]

No, only on the glow plug cycle.

Tried pulling a code and only got a 12. Checked the sensors and plugs. Unplugged one that was loose and plugged it back in (near the end of the transmission on the driver's side) and it ran perfectly for about 5 minutes, all gears worked and went back into limp mode, and it feels like the torque converter is now locking in reverse and drive. Once it's moving and gas is applied it stays running. This thing is driving me nuts!

 

[Mogman]

Tried pulling a code and only got a 12. Checked the sensors and plugs. Unplugged one that was loose and plugged it back in (near the end of the transmission on the driver's side) and it ran perfectly for about 5 minutes, all gears worked and went back into limp mode, and it feels like the torque converter is now locking in reverse and drive. Once it's moving and gas is applied it stays running. This thing is driving me nuts!

Did you check for a code after it messed up? If you had disconnected the batteries before you may have erased the stored code.
Try to pull a code after driving it and getting the TCM warmed up, it is possible the TCM is failing, no normal code/action should cause the converter to lock up.
After that, while it was still "failing" I would pull power to the TCM, if the T/C lockup goes away it would point to a failing TCM
It is also possible a valve is failing but a good TCM should recognize this and set a code.

 

[Mogman]

To pull power, disconnect one of the leads from the transmission circuit breaker, that pulls both the switched and unswitched power from TCM and the 12V feed to the transmission solenoids/valves.
With no electrical power to the transmission, even with no wires going the the transmission the trans should simply be in limp mode at that point if the T/C is still locking up then that would indicate a transmission problem.

 

[kingConan]

Did you check for a code after it messed up? If you had disconnected the batteries before you may have erased the stored code.
Try to pull a code after driving it and getting the TCM warmed up, it is possible the TCM is failing, no normal code/action should cause the converter to lock up.
After that, while it was still "failing" I would pull power to the TCM, if the T/C lockup goes away it would point to a failing TCM
It is also possible a valve is failing but a good TCM should recognize this and set a code.

I did not. I was supposed to have the truck in a parade for a homecoming football game and it went south. Great advice though. I'll give it a shot when I get back into town. Does the TCM have to be year/model specific? I have access to a handful of TCMs but all different models and years.

 

[Mogman]

I did not. I was supposed to have the truck in a parade for a homecoming football game and it went south. Great advice though. I'll give it a shot when I get back into town. Does the TCM have to be year/model specific? I have access to a handful of TCMs but all different models and years.

IFAIK any HMMWV TCM will work, the GM style has a chip that contains stuff like shift points so those may be a little off without swapping the chips, The PCS controller is universal

 

[kingConan]

IFAIK any HMMWV TCM will work, the GM style has a chip that contains stuff like shift points so those may be a little off without swapping the chips, The PCS controller is universal

Here is an update. After adding the transmission light and not being able to pull codes other than 12, swapped the TCM. The torque converter is not locking up anymore, and I have 1st and 2nd gears. The shift points are different. My truck is an 04 M1123. The donor TCM is an 07 M1123. Any ideas?

 

[Mogman]

Here is an update. After adding the transmission light and not being able to pull codes other than 12, swapped the TCM. The torque converter is not locking up anymore, and I have 1st and 2nd gears. The shift points are different. My truck is an 04 M1123. The donor TCM is an 07 M1123. Any ideas?

There should not be a significant difference, you still could have other issues like TPS calibration.
I would think if you were not shifting into 3rd or 4th you may have a code now, have you read the codes after test driving?

 

[kingConan]

There should not be a significant difference, you still could have other issues like TPS calibration.
I would think if you were not shifting into 3rd or 4th you may have a code now, have you read the codes after test driving?

Not yet. Trying to juggle between work haha. Will do and let you know

 

[kingConan]

Not yet. Trying to juggle between work haha. Will do and let you know

Pulled the codes. I have an 83 (TCC) and an 85. Could the replacement of the TCM be an issue, and can it be reprogrammed? As of now I am planning on replacing the TCC, filter and fluids. Also, when I pull the output speed sensor there is a little fluid in there. Any input is appreciated

 

[Mogman]

There is no user programming for that TCM
I could be a wiring issue on #83 or the old TCM fried the solenoid
The #85 could also be a wiring issue, as bad sensor or the transmission is slipping.
Also check to see if there is any fluid in the main harness connector at the trans.
Otherwise the troubleshooting guide will help you figure it out.