Ehy am i getting service park assist system on my dash

What make , model , year ? control module probably has DTC - diagnostic trouble code stored . Your best bet , take it to a qualified repair shop that has service repair info. an a scan tool that can view these code's .

control module

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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.

where is the parking assist sensor??

{: ) The "Service Park Assist" message cannot be erased or reset until the main cause of the problem is resolved. It will just keep on coming back. Let's say one or more of the park assist sensors are faulty, you should have it repaired or replaced first before the scan tool can successfully clear the trouble codes that were present then.
The SERVICE PARK ASSIST message is a reminder that a fault has been detected by the parking assist system and it will disable this system until the problem is being addressed. A scan tool can effectively trace the cause of the fault.

{: ) 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.

{: ) When the park assist system detects a hitched object behind your vehicle, it will normally display that "Park assist Blocked" message. You can still drive safely even with that message. When you're done, just remove the hook off. Turn off engine for a few minutes. turn it on again and drive your truck around for 30kmh or so, then test again the park assist system.

{: ) 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).

what is the process on how to reset the rear park assist light that comes on the instrument cluster on the dash?

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.