Park assist shut off intermittantly and now display reads "service park assist" permanantly. Dealer will not fix even tho' was warranty repair in Dec(less than 6 mos later problem was brought to their attn) How do I replace sensor on my own as they want a lot of $$$ and are they all the same or specific to the location on the bumper??

I not sure what the problem is but I do know if you back up over five miles per hour the park assist will shut down in reverse and you will get a message to that effect on the dash. I had the same problem with one of mine and the dealer told me that it is designed that way to shut down. Try backing up under five miles per hour and see if you have the same problem. Hope this helps.

It sounds like the repair is not complete. I would suggest taking it to first the place that did the repair and if they do not help go to the dealer.

In short this is a dealer level repair as it requires special equip to test the system.

{: ) The driver information center (DIC) displays SERVICE PARK ASSIST when the object alarm module detects a malfunction in the parking assist system and the system is disabled. The DIC also displays SERVICE PARK ASSIST when a loss of communication occurs with the object alarm module. Usually this is caused by faulty components or wirings. Better visit your dealer if still under warranty, for one park assist sensor only costs too much. If your bumper had been knocked off or had previous repairs outside the dealership, that's another thing.
The PARK ASSIST OFF message is displayed in the DIC when the parking assist system is disabled due to conditions that disable or inhibit the system. The object alarm module requests the DIC display PARK ASSIST OFF when it detects one of the following conditions:
• The parking assist system is manually disabled using the driver information center (DIC). • An object is attached to the rear of the vehicle, such as a trailer, bicycle rack, trailer hitch receiver, or tow bar. • The object alarm sensors are covered by snow, mud, dirt, slush, or ice. • The vehicle bumper is damaged, • Excessive paint thickness on a replacement object alarm sensor. • The object alarm sensors are disrupted by vibrations, like those caused by a large nearby vehicle or from heavy equipment such as a jackhammer.

{: ) SERVICE PARK ASSIST The driver information center (DIC) displays SERVICE PARK ASSIST when the park assist module detects a malfunction in the object detection system and sends a request to the DIC for display of the message. The DIC also displays SERVICE PARK ASSIST when there is a loss of communication with the park assist module.
PARK ASSIST OFF The PARK ASSIST OFF message is displayed in the DIC when the park assist system is disabled due to conditions that disable or inhibit the system. The red LED in the rear display, as well as, the telltale in the switch will be lit, notifying the driver the PARK ASSIST system is disabled. The object alarm module requests the DIC via the serial data circuit to display PARK ASSIST OFF when it detects that one of the following conditions is true:
• The object alarm system is disabled through DIC vehicle customization feature. Refer to the Owners Manual for more information. • An object is attached to the rear of the vehicle, such as a trailer, bicycle rack, or hitch receiver. • An object is hanging out of the endgate. • The park brake is not fully released. • The system receives vibrations from a large nearby vehicle or from a heavy equipment such as a jackhammer. In the case of objects attached to the rear of the vehicle such as a trailer, hitch receiver, or a bicycle rack, or objects hanging out of the endgate, the rear parking assist (RPA) will have an Automatic Object induced disable feature where the RPA will determine if the rear object is moving with the vehicle. If the RPA detects such a condition, the park assist will be disabled. The PARK ASSIST OFF message will continue to be displayed until the trailer hitch receiver is removed and the vehicle is driven forward above 24 km/h (15 mph).

better to order the shifter handle from the dealer and replace it

Take it back to the dealer/supplier - it should be fixed under warranty.
If you can't get it back to supplier, take it to the nearest repair/service shop that is authorised to perform manufacturer warranty work.

I had this situation too, exactly. Everybody told me it was probably a rear bumper sensor gone bad, but at least in my case, no such luck. It was the Park Assist Module, basically the control computer for the whole system. A new one fixed it, but was about $300.

Take it back to the dealer. There is a Technical Service Bulletin on the wiring for the Park Assist.

The park assist system detects objects 59 inches or less in back of your vehicle, to warn u so u don't strike the object. I'm guessing that since the service park assist system comes on in the ice and snow, the monitor is detecting something (ice and snow covering the sensor). If u clean off the snow and ice, the message should shut off.