U0268 on 2017-2018 Buick LaCrosse: Lost Communication with Object Detection Module

What's Unique About the 2017-2018 Buick LACROSSE

On this generation of the Buick LaCrosse (and its platform mates), the side object detection modules are situated in the rear bumper corners, an area highly susceptible to moisture, road salt, and debris. This placement makes the wiring connectors prone to corrosion and the modules themselves vulnerable to damage from minor impacts, leading to frequent communication failures. A notable GM-specific issue is that a faulty diagnostic tool cable can sometimes falsely trigger this code during a scan; the object detection modules communicate on a specific serial data bus on DLC pins 3 and 11, which may be unused by older or damaged scan tool cables. A further issue, detailed in TSB PIT5622B, is that the plastic brackets holding the modules can break from minor impacts, causing the sensor to become misaligned and disable itself over time, even without setting a communication DTC.

Diagnostic Flowchart

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

Symptoms You May Notice

• "Service Side Detection System" or "Service Driver Assist" message on the Driver Information Center (DIC)
• Blind spot warning lights in the side mirrors do not illuminate
• No audible or visual alerts for rear cross-traffic when in reverse
• Adaptive Cruise Control may be disabled if the vehicle is equipped with it
• In some cases on related platforms, the warning lights in the mirrors may stay on constantly.
🎬 Watch: Understanding the Service Side Detection System warning message.

Most Likely Causes

1. Wiring Harness or Connector Corrosion/Damage 🔴 High Probability The modules are located in the rear bumper, exposing the connectors to road spray, salt, and moisture. This leads to corrosion, often seen as a green or white crusty residue on the connector pins, which degrades the signal. Water can also wick up the copper wire under the insulation, causing damage further up the harness.
   How to confirm: Visually inspect the wiring harness and connector pins for the affected module behind the rear bumper cover. Check for corrosion (white or green powder), bent pins, or broken wires. Wiggling the harness while monitoring the system with a scan tool may reveal an intermittent fault.
   Typical fix: Clean the connector terminals thoroughly with a specialized contact cleaner. If corrosion is severe, wires are broken, or pins are damaged, the connector pigtail or a section of the harness will need to be replaced. This often requires splicing wires with solder and heat shrink for a durable repair. 🎬 See this walkthrough for repairing the module and wiring harness.
   Est. part cost: $25-$100
2. Failed Side Object Detection Module 🟡 Medium Probability Internal electronic failure of the module can occur from vibration, moisture intrusion, or age. A short circuit within the module can also bring down the entire object detection communication network, as seen in diagnostic videos on related platforms. 🎬 Watch: How a shorted module can take down the network.
   How to confirm: After confirming that the wiring, power, and ground to the module are good, the module itself is the prime suspect. A professional scan tool will be unable to communicate with it directly. Swapping the left and right modules (if they are interchangeable) can also confirm the fault if the code follows the module.
   Typical fix: Replace the failed Side Object Detection Module. The new module must be programmed to the vehicle's VIN and calibrated using GM's Service Programming System (SPS) software.
   Est. part cost: $250-$600
3. Loss of Power or Ground to the Module ⚪ Low Probability
   How to confirm: Using a multimeter, check for 12V power and a solid ground connection at the module's electrical connector. Check the fuse for the Driver Assistance Systems (on a related Chevy Malibu, this is in the interior fuse box on the driver's side).
   Typical fix: Repair the broken wire or replace the blown fuse. If it's a bad ground, clean the grounding point to bare metal and re-secure the connection.
   Est. part cost: $1-$20

Rare But Worth Checking

• Faulty Diagnostic Tool or Cable: Per TSB PIT5441C, a known issue exists where a problem with the technician's Multiple Diagnostic Interface (MDI) tool or its cable can induce false communication codes, including U0268. The object detection bus uses specific pins (3 and 11) on the DLC that may not be properly accessed by a faulty tool. This should be ruled out before replacing any parts on the vehicle.
• Improper Module Mounting/Alignment: Per TSB PIT5622B, a minor bumper impact, sometimes with no visible external damage, can break the plastic brackets (heat stakes) that hold the module to the fascia. The module becomes misaligned and, after a period of driving, learns its incorrect position and disables the system, often displaying a "Service Side Detection System Unavailable" message *without* a U0268 code. However, this physical damage can also be the root cause that leads to a U-code. The fix involves repairing the mounting and often replacing the module to reset its learned position.

Diagnosis Steps

1. Verify the complaint: Check for a "Service Side Detection System" message on the dash and confirm that the blind spot indicators are not working.
2. Scan all vehicle modules with a professional-grade scan tool. Note U0268 and any other communication codes.
3. IMPORTANT: Acknowledge TSB PIT5441C. Before proceeding, verify the diagnostic tool is not the cause by testing on a known-good vehicle or using a self-test loopback adapter (e.g., EL-47955-1).
4. Check the fuse related to the driver assistance or active safety systems. On related platforms, this is in the interior fuse panel.
5. Gain access to the side object detection modules. This requires removing the rear bumper cover, which typically involves removing screws in the wheel wells, fasteners underneath, and removing the tail lights to access mounting bolts inside the trunk.
6. Visually inspect the wiring harness and connector for the module that is not communicating. Look for green/white corrosion, chafed wires, or physical damage.
7. Inspect the physical mounting of the module. Per TSB PIT5622B, check for broken plastic brackets or any sign of looseness, which could indicate a past impact.
8. If the wiring and mounting appear intact, disconnect the module and use a multimeter to test for 12V power and continuity to ground at the connector.
9. If power and ground are present and the wiring is good, the Side Object Detection Module has likely failed and requires replacement.
10. After replacement, the new module must be programmed and calibrated by a qualified shop using GM's Service Programming System (SPS).

Parts You'll Likely Need

• Side Object Detection Module (OEM #84729107 (supercedes 84690957, 84729103, 84820654); 42625292 (supercedes 23163923, 23395350, 23395351, 84121020, 84121021)) — This radar sensor module is the component that most commonly fails internally due to moisture, vibration, or an internal short, causing the communication loss.
  Trusted brands: GM Genuine Parts, ACDelco
  OEM price range: $350-$600
  Aftermarket price range: $250-$450
• Wiring Harness Connector Pigtail — If the connector itself is damaged by corrosion beyond cleaning, replacing the pigtail by splicing it into the existing harness is the necessary repair.
  Trusted brands: ACDelco, Dorman
  OEM price range: $40-$75
  Aftermarket price range: $25-$50

Related Codes That Often Appear With This One

• U0269 — This code is for the opposite side's object detection module ('Lost Communication With Side Object Detection Module B'). They often appear together or in sequence as they share the same communication bus and are prone to the same environmental failures.
• U026A — This indicates a lost communication with the front view camera. If the entire object detection bus has a problem (e.g., a shorted module or wiring fault), multiple modules on that network may set codes simultaneously.

Technical Service Bulletins (TSBs) & Recalls

• PIT5441C: Advises that diagnostic trouble codes U0268, among others, may be set due to an issue with the Multiple Diagnostic Interface (MDI) cable used by the technician, rather than a fault with the vehicle itself. It specifies the object detection bus uses pins 3 and 11 on the DLC.
• PIT5622B: Describes a condition where a module becomes physically misaligned due to broken mounting brackets on the rear fascia, often after a minor impact. This causes the module to learn an incorrect position and disable the system.

Platform-Specific Known Issues

• TSB #PIT5441C notes that technicians should inspect their diagnostic interface cable, as a fault in the tool itself can cause false U-codes related to the Object Detection System.
• TSB #PIT5622B identifies that a "Side Detection System Unavailable" message (even without a DTC) can be caused by a broken or misaligned module mounting bracket on the rear fascia, often from a minor impact.

Mechanic-Grade Diagnostic Values

• Single-Wire GMLAN Bus Voltage (at module connector or DLC pin 3/11) — expected: Actively toggling between ~0.2V (recessive state, logic '1') and ~4.0-5.0V (dominant state, logic '0') when measured with an oscilloscope or fluctuating on a multimeter.. Failure: Voltage stuck at a constant 0V (short to ground), a constant 12V (short to power), or a fixed intermediate voltage indicates a bus or module fault.
• Power Supply at Module Connector — expected: 12V (Battery Voltage) with Key On, Engine Off.. Failure: 0V or significantly low voltage indicates a blown fuse or a break in the power wire.
• Ground Circuit at Module Connector — expected: Near 0V, with less than 0.1 ohms of resistance to a known good chassis ground.. Failure: Voltage reading above 0.1V or high resistance indicates a poor ground connection, which is a common cause of module communication failure.

Scan Tool Commands That Help

• GM GDS2 (Global Diagnostic System 2): Side Object Sensor Module Setup / Learn — This function is mandatory after replacing a side object detection module. It programs and calibrates the new module to the vehicle. The left (master) module must be programmed, which also configures the right (slave) module.
• GM GDS2 (Global Diagnostic System 2): Module Diagnostics > Data Display — To view the live communication status of all modules on the object detection bus. This helps confirm which module is not responding before physically accessing it.
• GM GDS2 (Global Diagnostic System 2): Data Bus Diagnostic Tool — To passively monitor the serial data circuits to see which modules are 'awake' or not communicating, which is especially useful for intermittent faults.

Wiring & Ground Locations

• Object Detection Bus (at DLC) — Pins 3 and 11 of the Data Link Connector (DLC) under the driver's side dashboard.. These are the specific pins a technician must access to diagnose the object detection network. A fault in the diagnostic tool's connection to these pins can mimic a vehicle fault, as noted in TSB PIT5441C.
• Master/Slave Module Wiring — The data line from the vehicle network connects to the Left (Driver's Side) Object Detection Module first, which then loops to the Right (Passenger's Side) Module.. The Left module acts as the 'Master' and the Right is the 'Slave'. A failure in the Left module or its connector can cause both modules to stop communicating. All programming is performed on the Left module.
• G103 — On the left frame rail, located underneath the Starter Generator Control Module (SGCM) bracket on models equipped with the eAssist powertrain.. A GM Preliminary Information bulletin identifies a poor connection at ground G103 as a cause for multiple communication DTCs and no-start conditions on the 2018-2019 LaCrosse. A faulty ground can disrupt network communication for various modules.

Real Owner Repair Stories

• YouTube channel 'DIYMechanicPro' (2023 GMC Acadia Denali (shares similar ADAS architecture with the LaCrosse)) — Multiple failed systems including blind spot monitoring, rear parking assist, and hands-free liftgate.
  ❌ Tried (didn't work) The owner could not complete the repair at home.
  ✅ What actually fixed it The rear bumper was removed, revealing a failed module. The video shows the replacement process and highlights that the final, critical step of programming the new module requires dealer-level SPS (Service Programming System) software, which the DIYer did not have access to. The video also noted a broken mounting bracket, confirming the issue described in TSB PIT5622B.

"I Checked Everything" — The Actual Cause

• The network equivalent of a 'smoke test clean' scenario is when all vehicle wiring and modules appear to be the source of the U-code, but the actual cause is external. Per TSB PIT5441C, a faulty MDI (the technician's scan tool) or its cable can fail to properly connect to the object detection bus on DLC pins 3 and 11, inducing false communication codes like U0268. The vehicle is fine; the diagnostic tool is the problem.

OEM Part Supersession History

• 84690957, 84729103, 84820654 → 84729107 — Updated design or manufacturing process by GM.
• 23163923, 23395350, 23395351, 84121020, 84121021 → 42625292 — Updated design or manufacturing process by GM.

Model Year Variations Within This Range

• 2018: The 2018 model year introduced a new standard 2.5L 4-cylinder eAssist mild-hybrid powertrain and a new 9-speed automatic transmission for the optional V6 engine (the 2017 V6 used an 8-speed). While these are significant powertrain changes, they do not directly alter the design or diagnosis of the separate Side Object Detection system.