LML Allison falling out of Reverse

[FROGMAN524]

Every now and then my 13,000 mile trucks falls out of reverse when backing up and it always feels like I just rear ended somebody. The R on the dash blinks and I put it in Park and back in Reverse and it seems to work after that. This doesn't happen every time I back up but recently it's about every other time or maybe every 3rd time. I've read in other threads it's a torn C3 piston but my warranty is surely voided so I don't want to tear the trans out. I have no issues in forward gears either.




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[DU102]

You run the hotter tunes a lot? I put 24,000 on my tuned lml tranny holding up so far, but I normally stay on the 100hp tune for daily driving, hope yours is not going out

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[FROGMAN524]

I've always run the big tune daily since about 600 miles unless towing


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[rcr1978]

I would say a pin in a connector could be bent, loose, backed out, chafed wire, or nsbu switch. I doubt it's a torn c3 otherwise you would have troubles in forward gears 3rd &5thto plus 11+ trans has different apply pistons. Any codes?

 

[FROGMAN524]

No codes


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[NC-smokinlmm]

Your 4x4 work?

 

[Mike L.]

No codes


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And you read them with what?

 

[FROGMAN524]

And you read them with what?

My CTS2.

 

[FROGMAN524]

Your 4x4 work?

4x4 works fine but when the truck was nearly new a I had an issue when in 4x4 Low the trans did something similar with the D flashing on the dash and I got a message on the dash about servicing the 4x4 system. The issue never recurred so I didn't take it to the dealer.

 

[onebaddmaxxx]

My CTS2.

Not good enough

 

[NC-smokinlmm]

Not good enough

I'd be willing to bet it's something in the transfer case

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[FROGMAN524]

I might have to got to the dealer to have them check for codes. What codes will the CTS2 not find or display?

 

[oscyjack]

It won't display anything but a generic trans code iirc. A good snap on unit does most but I'm pretty sure the tech2 is still the "one"

 

[Chevy1925]

I might have to got to the dealer to have them check for codes. What codes will the CTS2 not find or display?

it will only check codes in the ECM and nothing else.

 

[FROGMAN524]

Besides a Tech II is there another device I can purchase to check TCM and BCM codes as well?

 

[oscyjack]

My snap on does most of what a tech 2 does at least as far as I've explored with it on the truck. but it's also multiples more expensive. Make a friend at the dealer or look online for a used one.

 

[FROGMAN524]

Ok I will ask at the dealer if they can just scan for codes I am not seeing. Don't you have to update the Tech II constantly and pay for those updates?

 

[SoCalMike]

Do you have an autocal? That should read trans codes.

 

[Mike L.]

Ok I will ask at the dealer if they can just scan for codes I am not seeing. Don't you have to update the Tech II constantly and pay for those updates?

If the LML is later than '13; the Tech 2 won't work. You will need an MDI unit which needs no updates.

 

[FROGMAN524]

If the LML is later than '13; the Tech 2 won't work. You will need an MDI unit which needs no updates.

My truck is a 2016. Where can I get the MDI?