4L80 Stuck in 2nd Gear

[4x4nutz]

Just finished a build for Texas A&M and found the transmission is stuck in second gear. This is a 1097 A2. When we first got it the shifter was super hard to shift, but after some WD-40 and a little work, it shifted fine. It will still shift into neutral and reverse, but when you put it into overdrive, it stays in second. I am not a transmission guy, and I realize it may also be the TCM, so hopefully someone here can help a fella out.

 

[springer1981]

2nd gear is a default limp mode gear. You probably have a power issue to the tcm or a controller problem. Might be a circuit breaker issue or transmission power relay. Mogman will come along shortly and post a troubleshooting guide for you.

 

[Mogman]

Here you go.
Sorry my first post was wrong..

 

[4x4nutz]

2nd gear is a default limp mode gear. You probably have a power issue to the tcm or a controller problem. Might be a circuit breaker issue or transmission power relay. Mogman will come along shortly and post a troubleshooting guide for you.

Damn...that may be good news. Thanx....I will give y'all an update.

 

[Autonomy_Lost]

When this happened to mine, it was a broken wire resulting in no power to the TCM. Fixed that and it shifted fine.

Do you have a trans light when in the run position with the engine stopped?

 

[4x4nutz]

When this happened to mine, it was a broken wire resulting in no power to the TCM. Fixed that and it shifted fine.

Do you have a trans light when in the run position with the engine stopped?

Lol...my transmission warning light is inoperable...

 

[Mogman]

Lol...my transmission warning light is inoperable...

Could be because the TCM has no power.

 

[Mogman]

Also be cautious as the transmission runs on 12V the power relay that switches the 12V to the TCM has a 24v coil.

 

[4x4nutz]

Another question, I have another TCM, but it's off a turbo 1151...will it work?

 

[springer1981]

Another question, I have another TCM, but it's off a turbo 1151...will it work?

Why would you try that without first troubleshooting the problem? If it is a power issue that definitely won't help.

 

[Autonomy_Lost]

Lol...my transmission warning light is inoperable...

So was mine...until I got power to the TCM.

 

[springer1981]

I'd check page 52 and 107 of the pdf that Mogman posted and go from there.

 

[nikojo]

If the TCM were to be completely disconnected, ie remove all three connectors at the transmission, ie not just lose power but also physically disconnect the connectors.......would it still be able to operate in limp mode??

 

[springer1981]

If the TCM were to be completely disconnected, ie remove all three connectors at the transmission, ie not just lose power but also physically disconnect the connectors.......would it still be able to operate in limp mode??

I'm not an expert by any means but when I did my 4L80 conversion I spoke with a TCM manufacture in depth about the operation of the transmission and how the TCM works. My understanding based on that conversation (over a year ago), the transmissions defaults to 2nd gear with loss of control. Since everything else electronic deals with sensors, solenoids and lock up, I get the impression that it would work. The electronics control the shifts and then the lockup. The sensors tell the TCM what's going on to so it knows when to shift.

Park obviously would work, reverse doesn't shift or lock up so I suspect it would work. Drive should default to 2nd but would not shift to any other gears. I think it would work with all the connectors disconnected but that is really no difference than just losing power.

 

[Mogman]

If the TCM were to be completely disconnected, ie remove all three connectors at the transmission, ie not just lose power but also physically disconnect the connectors.......would it still be able to operate in limp mode??

Yes it will operate in 2nd gear only.

 

[4x4nutz]

Why would you try that without first troubleshooting the problem? If it is a power issue that definitely won't help.

Using the other TCM would hopefully be an option if the TCM that is installed is kaput (lol...after I check to see if I can fix the problem first). I was born 63 years ago, not yesterday.

 

[4x4nutz]

I'd check page 52 and 107 of the pdf that Mogman posted and go from there.

Thank you. Did exactly that. Will give you guys a follow up once I have figured out the issue.

 

[frauhansen]

i had the same some day ago... no error codes an the trans light... checking the lamp it self on a spare set of batterys with 24V... working.
But... behind the passanger Seat is a push-fuse... push and problem solved.

 

[4x4nutz]

Transmission light isn't on, there are no fuses or "fuse Buttons" to reset. There's nothing behind the passenger seat, the trouble shooting guide must be for a different model, or I'm too old to figure it out. The only wire disconnected (in the battery compartment) is a thick wire that was taped off. This thick wire is in a three wire bundle along with wire 57T and wire 599C. Here's some pics of what I have...
+

 

[Mullaney]

Transmission light isn't on, there are no fuses or "fuse Buttons" to reset. There's nothing behind the passenger seat, the trouble shooting guide must be for a different model, or I'm too old to figure it out. The only wire disconnected (in the battery compartment) is a thick wire that was taped off. This thick wire is in a three wire bundle along with wire 57T and wire 599C. Here's some pics of what I have...
+

.
It's no fun, but looking at that 4th picture - I think some good old fashioned elbow grease and some anti-oxidizing paste would help. If that looks that way then my guess there are other places that look the same. Disconnecting the battery terminals before you start might be really smart. No need to let the smoke out of your truck for no good reason.

Invest a full weekend. About 16 hours. From bumper to bumper.
A lot of things will be solved with a wire brush or a tooth brush and some cleaner...