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2007 Sierra 2500HD Classic LBZ
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Discussion Starter · #1 ·
Click this to see the Video of what’s going on.

This is a 2007 Sierra 2500HD classic with an LBZ.

It’s always done this since I’ve had it and I would like to fix it.

When I drive the truck in low range, I will get an ABS / Service Brake System warning and the speedometer drops to zero. Stopping and starting again will reset things. As soon as I switch back to high range the warning goes away.

My working theory is that the computer doesn’t know it’s in low range for whatever reason.

The transfer case and the output speed sensor are new but like I said, it’s been doing this since I bought it.
 

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Premium Member
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3,562 Posts
So you need a high level scan tool. You need to see if the tx case module is putting the message out to the other modules that the tx case is in 4lo. Without that message, many modules aren’t going to be happy.
 

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3,562 Posts
So should that be the bidirectional type?
Bidirectional just means that the scan tool has the ability turn things on and off. Any higher end Snap On or GM scan tool should be able to read the data you need to see.
 
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