I've been getting the Service Stability System on my DIC for the past week along with my ABS and Trac Off lights staying on. I took it to the Pontiac dealer today and got these codes:

C1221
C1225
C1232
C1288

I'm told the top 3 are my ABS sensor on left front wheel and the last one is my steering position sensor. The wheel bearing hubs are under warranty so that'* not a problem to replace, but i hear that replacing the intermediate shaft is expensive?

DTC C1221 LF Wheel Speed Sensor Input Signal is 0
DTC C1225 LF Excessive Wheel Speed Variation
DTC C1232 LF Wheel Speed Circuit Open or Shorted
DTC C1288 Steering Sensor Circuit Malfunction

You have warranty on the bearing but not the steering?
Replacing the front wheel bearing will clear the top 3 codes, assuming they checked the wheel speed connector/harness and all was good.

How are the 2 related? Did you hit a huge pot hole and whack both your steering and left wheel?

Loss of 5 volt reference or ground on circuits can throw weird codes. It is unlikely to be a sensor issue in this circumstance, as the likelihood of having 2 sensors simultaneously fail is quite low. The common factor in this instance is the fact that the 5 volt reference and ground are shared by both sensors.

The steering position sensor has been the most common cause of the service stability system, however a bad wheel speed sensor can also cause it. The intermediate shaft is moderately expensive, but is a different issue than the steering position sensor. As PDad mentioned, it does seem strange that the hubs would be covered, but not the steering components.

The extended warranty on my car only covers the powertrain. I payed for the 2 front hubs to be replaced several months ago which cost me $340 total. They should still be under warranty as i believe they were at least a year warranty. That'* why the hubs are covered and not the shaft. Seems like my hub harness is having problems with all those codes from it. I'll have to take the wheel off when i get a chance and see if the harness is still okay.

I believe the steering sensor code has been there for a while as i get the occasional Service Stability message, but the continuous Service Stability message has been there every time i drive the car for about the past week. Those wheel hubs are only a few months old and should still be under warranty, but first thing i'll do is check the harness to make sure it'* ok.

Are the wheel speed sensors part of the wheel hubs? did you get them replaced at the same time the hubs were replaced?

Yes, the sensors are embedded in the hub. Replace the hub, replace the sensor.

This is a TSB on the steering position sensor replacement to give you an idea of what is involved.

Steering - Revised Service Procedures

I'm betting you got a bad left front hub abs sensor. That bad sensor (integral with the hub) can throw the Stability message on the DIC. Since replacing my brand new hub with another all is quiet.

I just checked the harness and wires from it, everything seems well, so must be the sensor. :(

Finally got the car in the air today. We checked the harness and wires again and all seemed fine, so we changed the hub. All works great now and no codes, but the old hub was making noise inside like it was dried out or something. Anyway, was definitely a bad sensor.