Service park assist message. I replaced all 4 sensors and wiring harness at bumper. Vehicle was never in accident.

Probably needs the computer codes reset.

Hi I don't know the vehicle but sounds as if the park assis on all the time not turning off see if your reverse lights are working correctly, may be getting a feed buck into the unit keeping it turned on.

where is the parking assist sensor??

1. Open liftgate.

Fig. 12

1. Remove two push pin fasteners per side at the liftgate tower area (Fig. 12).
2. Hoist and support vehicle with safety stands, as necessary.

Fig. 13

1. Disconnect the park assist wire connector under the vehicle and the push pin fasteners attaching wire harness under the vehicle (Fig. 13)
2. Remove the four push pin fasteners attaching rear fascia to reinforcement bumper.
3. Remove two screws (each side) attaching fascia to rear fascia bracket in the wheelhouse.
4. Remove the screw on each side attaching the upper fascia in the tail lamp bucket area.
5. Remove rear fascia from vehicle by lifting sides of fascia up and outboard to release from rear fascia brackets.
6. Place fascia on a clean surface.

Fig. 14

1. Remove park assist sensors, if necessary (Fig. 14).

Fig. 15

1. Remove spring clips attaching upper and lower fascia together (Fig. 15).
2. Using a trim stick release locking tabs and separate the upper and lower fascia.

Fig. 16
Fig. 17

1. Remove move the bright chrome molding from the upper fascia (Fig. 16). Using a trim stick, starting at the out edge of the fascia release the locking tabs (Fig. 17). Grip the molding and pull outward from the fascia while releasing the locking tabs.
2. Remove molding from fascia.

INSTALLATION

1. Place bright chrome molding in position on the upper fascia.

Here you go

#PIT4878: Service Park Assist Message / LEDs Stay On Or Inop - keywords B0968 inoperative lamp led light lit module reverse urpa - (Jun 12, 2009) Subject: Service Park Assist Message/ LED's Stay On or Inop Models: 2007-2009 Chevrolet Silverado 2007-2009 GMC Sierra With RPO UD7

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern: Some customers my comment of a Service Park Assist Message on the DIC and/or the LED indicators at the right rear pillar staying on or inoperative. This concern could be caused by the wiring harness to the LED indicators being pinched under a ground eyelet at the right rear pillar, as shown below.


other issues could be the problem such as poor connections at each sensor or damaged sensors. to clear URPA codes,place ignition in run,(engine OFF),shift into reverse and turn key OFF.place shift lever into park and retest operation of URPA. if still inop URPA code(s) need to be retrieved before further diagnosis can be accurately done.

{: ) The PARK ASSIST OFF message will be displayed 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.
The SERVICE PARK ASSIST message will be displayed when the object alarm module detects a malfunction in the parking assist system and the system is disabled. It could be one of your sensors is at fault or even the module.

{: ) 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.

Check the system for DTC'S - diagnostic trouble codes should be the first step in the diagnostic process . Then reading factory service repair manual how the system works , viewing wiring diagrams .
Object Detection Description and Operation
Ultrasonic Rear Park Assist Operation
The ultrasonic rear park assist system senses how close the vehicle is to an object. The distance is determined by the 4 object sensors located in the rear bumper. The object detection system will notify the driver when backing up at speeds less than 8 km/h (5 mph). The object detection system will use the rear parking assist (RPA) display and the radio speakers for notification.
When the ignition is ON and the vehicle is placed into reverse, the object detection system performs a bulb check. During the bulb check, the 3 indicators on the RPA will illuminate for approximately 2 seconds to indicate that the system is working. The object detection system performs a bulb check and operates when the following conditions are present:
• The ignition is ON.
• The vehicle is placed in REVERSE (R) for rear parking aid.
• The vehicle speed is less than 8 km/h (5 mph). At speeds greater than 8 km/h (5 mph), the object detection system is disabled. The red indicator flashes to warn the driver that the object detection system is disabled.
The object detection system senses how close the vehicle is to an object. The distance is determined by the 4 object sensors located on the rear bumper. When the system detects an object, one of the following will occur:
• If the object is less than 0.3 m (11 in) away from the vehicle, the amber outside, amber middle, and the red outside indicators flash and the chime sounds continuously for 3 seconds.
• If the object is less than 0.3-0.5 m (11-20 in) away from the vehicle, the amber outside, amber middle, and the red outside indicators are ON.
• If the object is 0.5-1.0 m (20-40 in) away from the vehicle, the amber outside, and the amber middle indicators are ON.
• If the object is 1-2.3 m (40-91 in) away from the vehicle, the amber outside indicator is ON with a single chime when the object is first detected.
Object detection system can detect objects 7.6 cm (3 in) wide and at least 25.4 cm (10 in) tall. It cannot detect objects above the level of the roof.
If the object detection system detects a malfunction, a diagnostic trouble code (DTC) will be stored and the object detection system will send a serial data communication message to the instrument panel (I/P) to SERVICE PARK ASSIST message on the driver information center (DIC). Then the chime will sound and the red indicator on the information telltale center will be lit continuously. The red LED in the rear display will be lit, notifying the driver that a malfunction exists. Message will clear once the driver acknowledges it.
Each object sensor is a three wire sensor that is both a transmitter and a receiver that comprises a signal circuit, a low reference circuit, and an 8-volt supply voltage circuit. The rear object control module supplies 8 volts to the object sensors via the object sensor supply voltage circuit and provides ground via the low reference circuit. The rear object control module triggers the sensors in a sequential loop and after each sensor transmits, the rear object control module uses the echo or signal return to calculate the distance and position of an object from the rear bumper. The rear object control module directly controls the RPA display.

Do you know what DTC'S are ?
DTC B0958 01: Parking Aid Rear Sensor 1 Left Corner Circuit Short to Battery
DTC B0958 06: Parking Aid Rear Sensor 1 Left Corner Circuit Short to Ground or Open
DTC B0958 08: Parking Aid Rear Sensor 1 Left Corner Circuit Signal Invalid
DTC B0958 21: Parking Aid Rear Sensor 1 Left Corner Circuit Incorrect Period
DTC B0959 01: Parking Aid Rear Sensor 1 Left Middle Circuit Short to Battery
DTC B0959 06: Parking Aid Rear Sensor 1 Left Middle Circuit Short to Ground or Open
DTC B0959 08: Parking Aid Rear Sensor 1 Left Middle Circuit Signal Invalid
DTC B0959 21: Parking Aid Rear Sensor 1 Left Middle Circuit Incorrect Period

DTC B0967 02: Parking Aid Switch Circuit Short to Ground
DTC B0968 00: Parking Aid Indicator Circuit


Your best bet , take it to a qualified repair shop.

faulty sensor in teh bumper or bad connection, im not sure where the main module is on them. most likely in rear pannel, dr or pass side, check for rock beaten wires under the back of the van.

Most likely the problem you are experiencing with the park assist is a fault in one of the sensors mounted in the rear bumper. I would not consider it to be a major fix, however there will be a few hours labor involved as the bumper cover needs to be removed to replace the sensors.