programming speed sensor after installing 40" tires?

[OrangeCrush]

So here's the deal. When I had the 37's on with 4.56 gears, when I programmed my tuner to reflect that, I would get an abs/brake light on.

The way around that was to program the tuner with 35's and a lesser gear ratio. It worked perfect, my speedometer was on the money and no lights.

Now that I've switched to 40" tires, I keep getting the same light on. I've tried a combination of tire sizes and gear ratios but to no avail... after you've driven for 10 miles, the light comes back on.

I called Diablo and they told me I had to have someone change the values in the ECM for something to do with speed sensor. When I called my GM tech buddy, he wasn't sure what Diablo was specifically asking to be changed.

So, for anyone that installed 40's, how did you get around this?

Thanks,

Mark