U0159 on 2015-2018 GMC Sierra 2500: Causes and Fixes for Park Assist Communication Loss

What's Unique About the 2015-2018 Gmc SIERRA 2500

For this generation of GMC Sierra (and its platform-mate, the Chevrolet Silverado), GM has issued a Technical Service Bulletin (TSB #PIT5507E) that directly addresses the U0159 code. The TSB notes that on some trucks, specifically 2016 models, a random "Service Parking Assist" message can appear at startup, setting a U0159 code that often disappears after an ignition cycle. GM developed an updated software calibration for the Parking Assist Control Module to resolve this specific intermittent issue, indicating that the problem is frequently software-related rather than a hardware failure.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• "Service Parking Assist" message on the driver information center (DIC), which may appear randomly at startup and clear after restarting the vehicle.
• Parking assist system is inoperative.
• The warning light for the parking assist system stays on.
• Parking sensor display on the infotainment screen may be frozen, show incorrect information, or be completely absent.
• Audible parking chimes are disabled or behave erratically.

Most Likely Causes

1. Software Glitch in Park Assist Module 🔴 High Probability → Shop Collision Avoidance Sensor As identified in TSB PIT5507E, 2016 models were particularly susceptible to setting a U0159 at startup due to a software issue that GM has since released a fix for.
   How to confirm: A GM dealer or a shop with access to GM's TIS2WEB service can check if the module's software calibration is outdated. The TSB specifically calls for reprogramming the K41 Parking Assist Control Module.
   Typical fix: Reprogram the Parking Assist Control Module with the updated calibration. This must be done by a dealer or qualified repair shop with the proper tools.
   Est. part cost: $0
2. Faulty Parking Assist Control Module (PAM) 🟡 Medium Probability → Shop Park Assist Control Module Like any electronic module, the PAM can fail internally over time due to heat, vibration, or internal component degradation. Water intrusion is also a risk.
   How to confirm: After confirming power, ground, and communication wires are intact, the module itself becomes the primary suspect. A bi-directional scan tool that loses communication with the module points to a module failure. The module is located behind the rear driver's side seat back.
   Typical fix: Replace the Parking Assist Control Module. The new module will need to be programmed to the vehicle. The most common OEM part number is 23381529, which has been superseded by newer numbers like 84987038.
   Est. part cost: $150-$300
3. Damaged Wiring or Connectors 🟡 Medium Probability The wiring for the parking sensors and module runs along the frame and near the bumpers, making it susceptible to damage from road debris, moisture, and corrosion, especially from road salt in winter climates. Connectors behind the rear wheels are a common failure point.
   How to confirm: Visually inspect the wiring harness for any signs of fraying, breaks, or corrosion. Pay close attention to the harness connectors for the modules located behind the rear wheels, as these are exposed to the elements and known to corrode.
   Typical fix: Repair or replace the damaged section of the wiring harness. Clean corroded terminals with electrical contact cleaner or replace the connector pigtail if damage is severe.
   Est. part cost: $20-$150
4. Blown Fuse ⚪ Low Probability A power surge or a short circuit in the sensor wiring can cause the fuse for the park assist system to blow.
   How to confirm: Check the fuses related to the park assist system. On these trucks, relevant fuses are located in the fuse boxes on the driver (left-hand) and passenger (right-hand) side of the dashboard. Specifically, check fuse F29 in the driver's side fuse box and F27 in the passenger's side fuse box.
   Typical fix: Replace the blown fuse. If the fuse blows again, it indicates an underlying short circuit in the module or wiring that needs to be diagnosed and repaired.
   Est. part cost: $1-$5

Rare But Worth Checking

• Faulty Body Control Module (BCM): While rare, the BCM acts as a central gateway for network communication. If it fails, it can disrupt communication with many modules, including the PAM, often setting multiple 'U' codes.
• Chafed Main Dash Harness: The K2XX platform has a known issue (TSB PIT5288) where the main dash harness can rub against a sharp metal bracket, causing various communication codes. While U0159 is not the primary code for this, widespread network issues could potentially trigger it.

Diagnosis Steps

1. Scan for all Diagnostic Trouble Codes (DTCs) with a tool that can read body and network codes. Confirm if U0159 is the only code, or if other modules are also offline.
2. Check for TSBs. Specifically, see if TSB PIT5507E applies, as a software reflash is the first recommended step for the intermittent startup issue on 2016 models.
3. Check the fuses for the Parking Assist System. Locate the fuse panels on the driver and passenger sides of the dashboard and inspect fuse F29 (driver) and F27 (passenger).
4. Visually inspect the wiring harness connected to the Parking Assist Control Module and the sensors in the bumpers. Pay special attention to connectors behind the rear wheels for corrosion or damage from road spray.
5. If wiring appears intact, locate the Parking Assist Control Module (PAM). It is mounted to the back wall of the cab, behind the driver's side rear seat. Verify its connector is secure and free of corrosion.
6. Using a multimeter, check for proper power (12V+) and ground at the PAM's connector. A lack of power or ground points to a wiring or fuse issue.
7. If power and ground are good, and a reflash is not applicable or does not solve the issue, the module itself is the likely culprit. Replace the Parking Assist Control Module and have it programmed by a dealer or qualified shop.

Parts You'll Likely Need

• Parking Assist Control Module (OEM #23381529 (superseded by 84987038)) — This module can fail internally or require a software update to fix the communication loss indicated by U0159.
  Trusted brands: ACDelco (GM Genuine), Dorman
  OEM price range: $200-$300
  Aftermarket price range: $150-$250

Technical Service Bulletins (TSBs) & Recalls

• PIT5507E: Addresses a random U0159 code at startup on 2016 models, recommending a module reprogram. It also covers false alerts from incorrect sensor hardware or environmental factors across 2015-2018 models.
• PIT5507C: An earlier version of the TSB which confirms the software update fix for U0159 on 2016 models and discusses false alerts in rain/snow.

Platform-Specific Known Issues

• TSB PIT5507E notes that on 2016 models, a "Service Parking Assist" message can randomly appear at startup and set code U0159. The fix is a software update for the Parking Assist Control Module.
• The same TSB also mentions that false alerts can be caused by using incorrect (non-scalloped) sensor rings on replacement sensors or by improper sensor installation, which could potentially lead to system faults.
• Corrosion is a significant factor for modules and connectors mounted behind the rear wheels, which are directly exposed to road salt and water. A video for a 2016 Denali showed a U0159 code caused by heavy corrosion in the side detection module connector, which is in a similar location.

Mechanic-Grade Diagnostic Values

• Low Speed GMLAN Serial Data Circuit Voltage — expected: Toggles between approx. 0V and 5V. A logic '1' (recessive state) is near 0V, and a logic '0' (dominant state) is driven to >4.0V.. Failure: Voltage stuck high (short to voltage) or low (short to ground), or no activity.
• Low Speed GMLAN Serial Data Circuit to Ground Resistance — expected: Greater than 100 Ω with ignition OFF and module disconnected.. Failure: A reading of less than 100 Ω indicates a short to ground in the serial data circuit.
• Parking Assist Control Module Ground Circuit Resistance — expected: Near 0 Ω between the ground pin at the module connector and a clean chassis ground point.. Failure: High resistance indicates a poor ground connection, which can cause the module to drop offline.

Scan Tool Commands That Help

• GDS2 (GM Diagnostic Software): SPS (Service Programming System) - Reprogram — Used to flash the K41 Parking Assist Control Module with updated software to fix the intermittent startup issue described in TSB PIT5507E.
• GDS2 (GM Diagnostic Software): SPS (Service Programming System) - Setup and Configuration — This function must be performed after programming a new or existing Parking Assist Control Module to ensure it is correctly configured for the vehicle's specific options and operates correctly.

Wiring & Ground Locations

• K41 — Behind the driver's side rear seat back, mounted to the back wall of the cab.. This is the designator for the Parking Assist Control Module itself, the module that is offline when U0159 is set.
• G401 — Located in the rear of the vehicle, likely on the rear body panel or frame.. This is a chassis ground point. A wiring diagram shows the Parking Assist Module's ground wire (BK-YE) connects here. A loose or corroded G401 would cut the module's ground, causing it to lose power and communication.
• X411 Connector — Under the vehicle on the driver's side, near the frame rail, in the area behind the fuel tank.. This is a major harness pass-through connector. TSBs for similar platforms note this connector is highly susceptible to internal wire breaks and corrosion from road spray, causing communication loss for multiple rear-mounted modules. A fault here could interrupt the Low Speed GMLAN circuit on its way to the K41 module.

Real Owner Repair Stories

• YouTube Channel 'Video Service Information' (2016 GMC Denali with 76,000 miles) — A 'Service Side Detection' message was displayed on the DIC and code U0159 'Lost communication with side detection' was stored.
  ❌ Tried (didn't work) The video implies diagnosis went straight to the harness after finding the code.
  ✅ What actually fixed it The connector for the side detection module, located behind the rear wheel, was found to have heavy corrosion in its terminals. The final repair was to replace the affected wiring harness and both side detection modules. This highlights the vulnerability of connectors in this area to moisture and salt.

Model Year Variations Within This Range

• 2016: TSB PIT5507E specifically highlights 2016 models as being prone to an intermittent U0159 code at startup that can be resolved with a software update for the K41 Parking Assist Control Module. While other years may be affected, the 2016 model year is the primary target for this software fix.