4L80E LIMP MODE

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MVFUNGUY
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4L80E LIMP MODE

Post by MVFUNGUY » Tue May 17, 2022 3:07 am

My M1114 is in limp mode (transmission light on). I bypassed the 15 amp breaker with a fuse and cleaned all connections in the battery box area.

When placing a jumper on A & E my light stays on solid. Once in awhile the light will slightly strobe and usually if you can get the light to slightly strobe you can here relays or solenoid flicker once or twice from the transmission.

Will the transmission light stay on if the TCM is bad?


Action
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Re: 4L80E LIMP MODE

Post by Action » Tue May 17, 2022 5:24 am

From your description, i read it as you jumped A and E and are driving like that?
How about a bit more detail of your process?
Did you disconnect the TSU / GPC before test? So the glow plugs do not cycle while the switch is in run.
Is the light on only when switch is in run?

Jason

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Re: 4L80E LIMP MODE

Post by MVFUNGUY » Tue May 17, 2022 7:16 am

Transmission light is off when truck switch is off. Comes on when you bring the truck to run, remains on when truck is started, and stays on until you turn truck off.

I have not driven the truck with the jumper in place. I'm only stating that when I turn the switch from off to on the light stays on solid and you might hear a click of a relay. Sometimes after you disconnect the battery and reconnect it. The light might flicker/strobe very quickly and if it does that you may hear relays of something making 2 clicks from the transmission area. (I have a video if you want me to text it to you)

I did not disconnect the GPC/TSU when I attempted the A & E jumper test, but I will when I get home tonight and reattempt.

I've cleaned all battery connections. Checked wires 1, 2, 3, 4 from relay. Bypassed circuit breaker with a fuse to make sure that was not the problem.
Tried grounding the TCM. I have a relay on the way and TISS/TOSS Sensors to swap out.

I've only drove the truck once around the block with a top speed of 25-30. FWD & REVERSE Seem fine at the low limp mode speeds.

Fresh Oil in all components of truck.

If I move the transfer case lever the T/C Lock light will come on. Also the brake lights work and the brake light on the dash illuminates when parking brake is set.

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Re: 4L80E LIMP MODE

Post by MVFUNGUY » Wed May 18, 2022 5:14 am

UPDATE:
Cleaned all battery connectors
Changed out 15 amp breaker
Checked #'s 1, 2, 3, 4 off relay in battery box
Changed out TOSS
Checked Brake Pedal Sending Unit it tested good.
I have 12.7V at the TCM checked both ground ports

Under the Humvee (M1114 ECV) above the Toss sensor there is a (# 290 double pin plug) not connected to anything, is that correct?

GPC unplugged. Jumper in ports A & E.

Truck trans light still stays on. If I disconnect the battery and reconnect I can get the trans light to quickly flicker/strobe and I can hear solenoids or relays clicking in the transmission. If light stays on solid there are no noises.

I am assuming my TCM is bad. I've read with Armor these trucks had higher shifting points. If buying a TCM is there a certain TCM I want to buy for a striped down truck. I believe my truck is a 2010 model. (Serv. No. 16196390)

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Re: 4L80E LIMP MODE

Post by Action » Wed May 18, 2022 10:43 am

The light should at least give you a 12 code to let you know it is in diagnostic mode. Are you sure A and E are jumped well? I use a sprung paper clip that holds itself in place.

Jason

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Re: 4L80E LIMP MODE

Post by 86humv » Thu May 19, 2022 4:44 am

Need to open trans TCM box, and see if its a GM TCM and open 2 screw panel to see if its corroded inside
and check what blue chip it has with a code on it: example { CZSW or CMBB,...Ect....}.
There's also a PCS brand that could be in there instead of the GM Tcm.
86 Hmmwv
Lots A parts
M101A2 trailer
M1102 trailer

MVFUNGUY
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Re: 4L80E LIMP MODE

Post by MVFUNGUY » Tue May 24, 2022 3:23 am

Issue was the TCM. I replaced it and the transmission came back to life.

Thanks


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