MikeG009Have a 2008 CTS 3.6 DI that displays "Service Power Steering" message on the DIC and has no power assist. My independent mechanic (non dealership) finally found the problem after several hours of troubleshooting. Vehicle also showed an ABS code but after checking individual components (ABS module and wheel sensors, steering rack and pump. etc.) No problems were found. The problem was two wires were rubbing against each other in the wiring harness that runs from under the engine computer around the rear of the alternator near the passenger side front of the vehicle. To repair, he put the car on a lift and removed splash shields to gain access. He completely unhooked the harness and pulled it out of the car. After checking each small individual wire he found where one wire had a small break in the insulation and another wire was completely broken. After splicing the wires back together, DIC message was cleared and power assist returned. He also covered all exposed wiring harness with insulated heat resistant covers and cable tied all wiring to reduce vibration and movement. Many previous posts have stated to check the harness near the firewall where it goes around the engine on the passenger side for this problem. This was found in a totally different area. Hope this may help someone tracking down this difficult problem.
Please can l get the contact information of your mechanic ?.
I am experiencing the same problem.