How do I fix park assist

First you need to read the code's to find out what the problem is , you don't just guess and replace part's . You really should take it to a qualified repair shop if you don't know that .
Parking Aid The parking aid system consists of the:

• parking aid sensors
• parking aid speaker
• parking aid module

The parking aid system is activated when the parking aid module receives a network messages from the instrument cluster indicating that the vehicle is in reverse. The parking aid system sounds a warning to alert the driver of stationary objects near the rear bumper when REVERSE is selected. The parking aid system assists the driver in detecting certain objects while the vehicle moves in reverse at speeds less than 4.8 km/h (3 mph). The parking aid system may not detect angular or moving objects.

Inspection and Verification

1. Verify the customer concern.

1. Visually inspect the following for obvious signs of electrical damage.
   
   Visual Inspection Chart Electrical
   • Smart junction box (SJB) fuse 18 (10A)
   • Circuitry
   • Connector(s)
   • Parking aid sensors
   • Parking aid speaker
   • Parking aid module

1. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.

1. If the cause is not visually evident, connect the diagnostic tool to the data link connector (DLC) and select the vehicle to be tested from the diagnostic tool menu. If the diagnostic tool does not communicate with the vehicle:
   • check that the program card is correctly installed.
   • check the connections to the vehicle.
   • check the switch position.

1. If the diagnostic tool still does not communicate with the vehicle, refer to the diagnostic tool operating manual.

1. Carry out the diagnostic tool data link test. If the diagnostic tool responds with:
   • CAN circuit fault; all electronic control units no response/not equipped, refer to Section 418-00 .
   • No response/not equipped for parking aid module, Go To Pinpoint Test A .
   • System passed, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs and carry out self-test diagnostics for the parking aid module.

1. If the DTCs retrieved are related to the concern, go to the Instrument Cluster Diagnostic Trouble Code (DTC) Index or the Parking Aid Module Diagnostic Trouble Code (DTC) Index.

1. If no DTCs related to the concern are retrieved, GO to Symptom Chart . Instrument Cluster Diagnostic Trouble Code (DTC) Index DTC Description Source Action U0159 Lost Communication With Parking Aid Module Instrument Cluster REPAIR all other DTCs first. If the DTC is still present Go To Pinpoint Test A . All Other DTCs - Instrument Cluster REFER to Section 413-01 .
   
   
   Parking Aid Module Diagnostic Trouble Code (DTC) Index DTC Description Source Action B1299 Power Supply Sensor Circuit Short to Ground Parking Aid Module Go To Pinpoint Test C . B1342 ECU is Faulted Parking Aid Module CLEAR the DTCs. REPEAT the parking aid module self-test. If DTC B1342 is retrieved again, INSTALL a new parking aid module. REFER to Parking Aid Module in this section. CLEAR all DTCs. REPEAT the self-test. B2477 Module Configuration Failure Parking Aid Module REFER to Section 418-01 . C1699 Left Rear Sensor Circuit Short to Battery Parking Aid Module Go To Pinpoint Test D . C1700 Left Rear Sensor Circuit Failure or Blockage Parking Aid Module Go To Pinpoint Test C . C1701 Left Rear Sensor Circuit Fault Parking Aid Module Go To Pinpoint Test E . C1702 Right Rear Sensor Circuit Short to Battery Parking Aid Module Go To Pinpoint Test D . C1703 Right Rear Sensor Circuit Failure or Blockage Parking Aid Module Go To Pinpoint Test C . C1704 Right Rear Sensor Circuit Fault Parking Aid Module Go To Pinpoint Test E . C1705 Left Rear Center Sensor Circuit Short to Battery Parking Aid Module Go To Pinpoint Test D . C1706 Left Rear Center Sensor Circuit Failure Parking Aid Module Go To Pinpoint Test D . C1707 Left Rear Center Sensor Circuit Fault Parking Aid Module Go To Pinpoint Test E . C1708 Right Rear Center Sensor Circuit Short to Battery Parking Aid Module Go To Pinpoint Test D . C1709 Right Rear Center Sensor Circuit Failure Parking Aid Module Go To Pinpoint Test C . C1710 Right Rear Center Sensor Circuit Fault Parking Aid Module Go To Pinpoint Test E . C1742 Rear Sounder Circuit Failure Parking Aid Module Go To Pinpoint Test F . C1743 Rear Sounder Circuit Short to Battery Parking Aid Module Go To Pinpoint Test F . U1900 CAN Malfunction - Missing Message Parking Aid Module REPAIR all other DTCs first. REPEAT the self-test. If DTC U1900 is still present, DIAGNOSE the system for a missing transmission range signal. REFER to Section 418-00 . U2051 One or More Calibration Files Missing/Corrupt Parking Aid Module REFLASH the parking aid module. If the DTC occurs after a software reflash, REFLASH the parking aid module again. If the DTC reappears after each attempt to reflash, INSTALL a new parking aid module. REFER to Parking Aid Module in this section. CLEAR all DTCs. REPEAT the self-test. Take your vehicle to a qualified repair shop before you cause more problems .

The ultrasonic rear parking assist (URPA)
The URPA is equipped with a switch located above the driver information center (DIC) that can be used to disable the system.Do you have it disabled ?
Diagnostic Trouble Code (DTC) Displaying
This vehicle is equipped with an on-board diagnostic display feature capable of displaying diagnostic trouble codes using the 3 indicators on the rear parking assist display. After the bulb check has been completed, the red outside indicator flashes to indicate a malfunction with the system. The module disables operation of the URPA system under this condition.
In order to enter the diagnostic mode, complete the following actions:
With the ignition turned OFF, short the rear parking assist diagnostic connector to ground while the vehicle is in PARK. For the location of the rear parking assist (RPA) diagnostic connector, refer to Object Detection Component Views . It's under the front of the center console , by the BCM - body control module.
Turn ON the ignition.
Place foot on the brake.
Shift the vehicle into REVERSE within 5 seconds.
If the vehicle is not shifted into reverse within 5 seconds after turning the ignition ON, the diagnostic mode will still be initiated. However, a reverse input wiring fault will be registered as sequence #7 as shown in the Diagnostic Indicator table below. Refer to Diagnostic Trouble Code (DTC) Clearing for the specific steps on how to clear diagnostic trouble codes. After the reverse input wiring code is cleared, repeat the diagnostic trouble code displaying steps in order to enter the diagnostic mode.
When the diagnostic mode is first entered, the rear parking assist display displays the amber outside indicator and the red outside indicator. Then, the indicators on the rear parking assist display will display one or more of the sequences in the table below to indicate where the fault exists within the rear parking assist system. Refer to Diagnostic Trouble Code (DTC) Clearing for the specific steps on how to clear diagnostic trouble codes.

Diagnostic Indicators #
State/Fault Location
Amber Outside
Amber Middle
Red Outside
Flashing
1
Start of Diagnostics
X
--
X
--
2
RR Corner Object Sensor and Wiring
X
--
--
--
3
RR Middle Object Sensor and Wiring
X
X
--
--
4
LR Middle Object Sensor and Wiring
--
X
X
--
5
LR Corner Object Sensor and Wiring
--
--
X
--
6
Chime Warning Wiring
--
X
--
--
7
Reverse Input Wiring
--
X
--
X
8
Important: This diagnostic pattern sets for an open sensor supply voltage circuit and sensor low reference circuit.
Sensor Supply Voltage Circuit and Sensor Low Reference Circuit
X
X
X
X
Flashes in the following sequence:
Amber Outside
Amber Outside and Amber Middle
Amber Middle and Red Outside
Red Outside
9
Important: This diagnostic pattern sets for a short to ground in the sensor supply voltage circuit.
Sensor Supply Voltage Circuit
X
X
X
--

where is the parking assist sensor??

{: ) 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.

{: ) 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).

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.

If your trac and abs are both on. the problem could be a wheel speed sensor.
on some GM cars this sensor is built into the vehichles hub unit. making the bering and sensor one sealed unit. cheap hub units can be gotten (under 100 bucks) at autozone

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.