The original rear end started making grinding noises and the wheels would get stuck so a used rear end was swapped in its place. A few weeks later we noticed that after 50 mph or so we would get a "Reduced Engine Power" message along with a Check Engine Light. We were not sure of the cause so we parked the Tahoe for a while. I thought that it couldnt be the rear end since the mechanic had checked out the RPO codes and got the VIN number to order the correct rear end. A couple months passed and I finally checked out the problem.

I pulled a P215B code for "Vehicle Speed - Output Shaft Speed (OSS) Correlation". This got me thinking that there must be something wrong with the rear end. I lifted up Tahoe, measured the circumference of the drive-shaft (about 32cm), and tied a string to it. Turned the driveshaft until the wheel turned 2 times and measured the length of the string that wrapped around the driveshaft (about 110cm).
110/32 = 3.4375. This led me to conclude that a 3.42:1 ratio rear end must have been installed.
I scanned the Tahoe while driving and found that when the VSS said 57 MPH, the Wheel speed sensors were reporting 51.5MPH.

Turns out that the rear end only had a 3 month warranty and we are past 4 months now. Going to try to get it swapped for a correct ratio (3.08:1) rear end, but if that fails, what options do we have now?

Is it possible to reprogram the computer for the new ratio considering the Escalades had a 3.42:1 ratio? I went to a dealer last week and after 6 hours of waiting they told me the only thing I could do was put in a new rear end or go aftermarket to reprogram the computer. Hypertech said they cant reprogram hybrids.

Is it necessary to swap out all the internals of the rear end to change the ratio? What would I need to purchase to change the ratio?

Thanks in advance for your help.

 

Depending on what rear axle they put in, you should be able to get just a Ring&Pinion for the ratio change.

The original was also a Locker.

Worst case would be after market Ring, Pinion, bearings, and differential.

Next possible surprise will be the wheel speed sensor compatibility, actually axle speed sensors. If they are not compatible with the brake computer...

 

All 4 wheel speed sensors return the same speed. Does this confirm the sensors are correct?

 

That's a good first sign. If slight circuit differences it may set nuisance codes.

 

It was the incorrect ratio causing the P215B code after 50+MPH. Had 3.08 ratio ring and pinion installed and it no longer throws the code. Problem solved

 

Good to hear. Thanks for the update.