5 speed Allison looks like 4 spds on the indicator

arroyoseccofarm · October 3, 2005

I have a new 2005 Sierra 2500 D/A.

I am no expert on these things but I read the documention carefully.

It appears from the transmission indicator above the steering column that there are four speeds, not 5.

Please help me understand.

Other thing that doesn't look like its "by the book" is messages on the DIC.

Owners manual says there is a fuel filter life message but there isn't one.

There is one for oil life. Does the fuel filter message only show when changing is needed?

Much thanks from a nubie!

MS3DALE · October 4, 2005

On your shift quadrant,Thats the way GM designed it,To only show 4 spds.on the display but you have 5,You run it in the "D" gear for normal driving which will be 5th gear or "Overdrive",If you need to lock out overdrive and run it in 4th gear simply press in the "Tow/Haul" mode button on the end of the transmission shifter for a few seconds and an indicator light on the cluster (On the upper RH side) will light up a "D" with a line through it,This means that you have "locked-out" overdrive and are in 4th gear.To put it back in overdrive,simply press the button in again for a few seconds until the light goes out.

Now if you just push the button in for a quick second,that will put you in the "Tow/Haul" mode.

You can do both if you need to,In other words you can lock out overdrive and be in the "Tow/Haul" mode both at the same time.

This "locking out" of overdrive only applies from the factory on '03-up trucks with the Allison Trans.,GM offers a kit to retro-fit the '01-'02 trucks but it is at the customers expense.

I believe your owners manual should explain everything in detail but thats the short explaination of it.

GM-Tech · October 3, 2005

It appears from the transmission indicator above the steering column that there are four speeds, not 5.
Please help me understand.

GM cheaped out and didn't design a separate DIC with a different PRNDL for those with an Allison? I don't know if that's the answer, but it's the only one I can think of.

I never looked for the fuel filter life message. I know it's supposed to be there, but don't really have any details on it. Maybe someone else here does.