Another HMMWV in limp mode

[m56-mike]

Hello all it’s been years since posting. I’m seeing some similar posts but none quite like my issue forgive me if I’m covering old ground. 2009 MMMWV 6.5 turbo 4 speed Truck 480 L no shift. Unit was sitting for god only knows how long. Ex marine corps unit
So
my trans is in second. Trying to shift one two or anywhere does nothing. Converter feels like it’s never quite locked up. Real mushy 30MPH engine screaming. Fluid levels all good. I changed my TPS at the urging of a hummer guy. No change. Messed with and tweaked adjustment on tps. No change.
So as suggested I jumped post A-E on the trans control module to “count the blinks” but I have none. In fact usually in other units, I thought you always got a quick trans light flash when starting. I have none. Ever. Including with the pins jumped.
I then took the 472 pin connector loose to my trans control module. I checked every pin for power. Both with the ignition on as well as with it off. No dc voltage anywhere. Shouldn’t something there be live? I then started looking behind the batt box. I found a resetting breaker that seems to have no power with the unit turned on or off. At least the top lug I could get too. I can see the trans relay nut getting to it involves more tearing apart and I was loosing light.
I think we have no DC to this trans& trans controls.
thoughts?

thanks Mike

 

[86humv]

Two wires with yellow marking should go to back battery pos. terminal to feed breaker and relay....also relays do get stuck on, or off.

 

[m56-mike]

Two wires with yellow marking should go to back battery pos. terminal to feed breaker and relay....also relays do get stuck on, or off.

I will look.

 

[mrfarb]

I had a similar experience - after confirming the wires are correctly connected at the battery, the relay behind the commander seat (on the same panel as the resettable fuse) needs to have 12v in. On my truck the relay was bad causing the exact same symptoms you are having. The TM (and Michael Vaden from Black Dog) helped immensely. Side note, in my case the replacement relay was also bad and had to get another, so make sure you bench test replacements too.

 

[Mogman]

Welcome to the SS forums
Do you have this?

 

[TOBASH]

Welcome to the SS forums
Do you have this?

Mogman, you post that TM so often that you need to include that transmission TM in your signature line.

 

[m56-mike]

Hey Guys
i did not have that exact version of the Trans trouble shooting manual. Thanks
I did poke around yesterday for a while. I have no power behind that passenger side seat the relay the self-resetting breaker none of those inputs are live with ignition on or off. I had someone mention the harness with the yellow markings are critical to be hooked to the batteries. i have two of those they are wrapped tight in that heat shrink type covering and come from under / behind that passenger seat tight to the doghouse under some insulation and travel up along the dough house / inner kick panel THEN go up under the A/ C ducting. I did find a pair of wires late yesterday in the battery box cut off short one pretty heavy gauge that looks like it goes in a straight line towards the trans thru the dog house hump the other is a lighter gauge that goes into one of those harnesses that heads back towards the relays and controls for the trans behind that seat. Again, cut off super short no way to identify the via number. I may try to power up one or both and see what happens.
the Gov Liq location this came from has employees buying and selling hummers, sounds like the y pick and choose the good ones. Mine was listed as running yet when i got there it had no starter, not a bad one None. im guessing they fragged this truck somehow and i just need to figure it out

Mike

 

[NDT]

That’s the root of your problem. DO NOT guess which wire is which, trace them out, the opposite end should be marked as well.

 

[TOBASH]

My humble advice… Temporarily use two wires to bypass and power up tranny to see if that helps.

Then you will know if you can drive.

After that fiddle with and or trace wires and replace the power breakers.

 

[m56-mike]

Going to look at another unit later today to see what I can.

 

[Mogman]

Trace that large wire it likely goes to the 14V tap on the regulator, that should be connected to the first battery positive (12V tap)

 

[m56-mike]

I had a similar experience - after confirming the wires are correctly connected at the battery, the relay behind the commander seat (on the same panel as the resettable fuse) needs to have 12v in. On my truck the relay was bad causing the exact same symptoms you are having. The TM (and Michael Vaden from Black Dog) helped immensely. Side note, in my case the replacement relay was also bad and had to get another, so make sure you bench test replacements too.

ok looking at lunch a buddies operational / Similiar unit Wire 290-291B is hot 12 volt power in regardless of igintion. If nothing else we should be able to get that live with 12 volt in and check trans operation a bit

thanks Mike

 

[m56-mike]

That’s the root of your problem. DO NOT guess which wire is which, trace them out, the opposite end should be marked as well.

I agree, i have no power at the 290-291-537 12 volt feed into the trans circuit breaker. Once i find out why and supply that i am confident this system will wake up,
then i have to make sure all 200 wires i deisconnected and tested are back where they belong etc

 

[m56-mike]

My humble advice… Temporarily use two wires to bypass and power up tranny to see if that helps.

Then you will know if you can drive.

After that fiddle with and or trace wires and replace the power breakers.

So. Know the relay needs 12v in. What else would you need to power up? That circuit breaker? I suited it fed among other things the relay.

 

[m56-mike]

So. Know the relay needs 12v in. What else would you need to power up? That circuit breaker? I suited it fed among other things the relay.

Ok ok it appears that relay is half 12 volt half 24 volt. So if we power up there we should know something.

 

[NDT]

Check the schematic in Supplement 7!

 

[Mogman]

Ok ok it appears that relay is half 12 volt half 24 volt. So if we power up there we should know something.

The schematic is pretty clear on what you need to know in that supplement I posted for you

 

[Mogman]

There are two 12V feeds to the TCM, one is hot all the time and the other is supplied by the relay, and yes that relay has a 24V coil to switch the 12V