U1538 on 2017-2018 Buick LaCrosse: Network Communication Fault Causes and Fixes

What's Unique About the 2017-2018 Buick LACROSSE

What's unique to this LaCrosse and its platform mates is a documented condition where high bus traffic on the communication network, combined with the PEPS module's startup process, can occasionally lead to this fault code. Unlike other GM vehicles where U1538 might point to a physical part like a driver's window switch due to water intrusion in a door harness, on the 2017-2018 LaCrosse it is most frequently a software anomaly that doesn't necessarily indicate a failed part. The TSB explicitly states to ignore code U0422 (which is set for the same reason) unless it is accompanied by U1538 and U1534, confirming this specific combination points to the software issue.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light or other malfunction indicator may be on
• No noticeable drivability symptoms in many cases
• Intermittent issues with keyless entry or push-button start
• Other communication-related trouble codes may be present (especially U0422 and U1534)

Most Likely Causes

1. Vehicle Software Anomaly at Startup 🔴 High Probability A specific TSB (#16-NA-407, later revised) was issued for this model year, identifying a condition where high bus traffic during startup causes the PEPS module to send invalid data. The TSB explains this leads the BCM to set the 'door open switch virtual device availability (VDA) to unavailable'.
   How to confirm: A GM dealership technician can check if the vehicle's software has been updated per TSB #16-NA-407. The code almost always appears as a history code with U0422 and U1534. The TSB advises ignoring U0422 unless U1534 and U1538 are also present.
   Typical fix: Reprogramming the relevant control module (BCM or HPCM) with updated software provided by the manufacturer via the Techline Connect service. 🎬 Watch: Step-by-step guide to reprogramming GM modules with Techline Connect.
   Est. part cost: $0
2. Weak or Failing Battery 🟡 Medium Probability → Shop Vehicle Battery Low voltage during engine cranking can disrupt communication between the many sensitive electronic modules, triggering various network codes. GM vehicles with Auto Stop/Start technology are particularly demanding on the battery.
   How to confirm: Test the battery's voltage and cold cranking amps (CCA) with a digital battery tester. A reading below 12.4 volts at rest or a failed load test indicates a weak battery. The vehicle uses an AGM battery, which requires a specific type of tester.
   Typical fix: Replace the vehicle's 12V AGM battery and reset the battery sensor module if applicable. 🎬 See how to reset the battery sensor module on a LaCrosse.
   Est. part cost: $170-$350
3. Wiring or Connector Issue ⚪ Low Probability While less common than the software issue for this specific fault, a loose connector or damaged wire on the LIN bus can disrupt communication. Unlike other GM trucks and SUVs, widespread issues with water intrusion in the LaCrosse door harness are not commonly reported for this code.
   How to confirm: Visually inspect wiring harnesses connected to the BCM and PEPS module. Use a multimeter to check for continuity and shorts on the relevant communication circuits, which requires a wiring diagram.
   Typical fix: Repair the damaged wire or secure the loose connector.
   Est. part cost: $5-$50

Rare But Worth Checking

• Failing Control Module (BCM or PEPS): While the TSB points to a software glitch, it is possible for one of the communicating modules to have an internal hardware fault. This should only be considered after software updates and wiring checks have been performed. Swapping modules for diagnosis is not recommended on these vehicles as it can damage both modules.

Diagnosis Steps

1. Scan for all stored DTCs. Note if U1538 is present with U0422 and U1534, as this strongly points to the TSB.
2. Check the vehicle's service history or contact a GM dealer to see if TSB #16-NA-407 has been performed. The TSB was updated several times, so ensure the latest version of the software is installed.
3. Test the 12V AGM battery's health, including state of charge and cold cranking amps. A weak battery is a common cause of electronic glitches during startup and can cause programming failures.
4. If the software is up to date and the battery is healthy, a technician would then proceed with network diagnostics. This involves checking for proper resistance (60 ohms on a typical high-speed bus) and using an oscilloscope to check the CAN bus waveform for abnormalities.
🎬 Watch: Advanced LIN bus diagnostics and module initialization walkthrough.
5. If no physical faults are found in the wiring, and the software is current, advanced diagnostics with a GM-specific scan tool would be needed to monitor network traffic and isolate a potentially faulty module. However, this is a very unlikely scenario for this specific code combination.

Parts You'll Likely Need

• 12V AGM Battery (OEM #ACDelco Gold 94RAGM (GM #88864542)) — A weak battery can cause unpredictable communication errors between modules during startup. This is often a contributing factor even if a software issue is the root cause. The vehicle requires a Group 94R AGM battery.
  Trusted brands: ACDelco, DieHard, Duralast
  OEM price range: $200-$400
  Aftermarket price range: $170-$350

Related Codes That Often Appear With This One

• U0422 — TSB #16-NA-407 explicitly states that U0422 (Invalid Data Received From Body Control Module) is often set alongside U1538 due to the same startup communication issue.
• U1534 — This code is also mentioned in TSB #16-NA-407 as being set in conjunction with U1538 for the same reason.

Technical Service Bulletins (TSBs) & Recalls

• 16-NA-407: States that on some 2017-2018 LaCrosse, Cadillac XT5, Chevy Bolt, and 2018 Equinox/Terrain models, DTCs U0422, U1534, and U1538 may be set due to a communication issue with the PEPS module at startup. It recommends a software update.

Platform-Specific Known Issues

• A documented software issue exists where high network traffic during startup can cause the PEPS module to send invalid data, setting codes U1538, U1534, and U0422. This is detailed in GM TSB #16-NA-407.
• The TSB explains the technical cause as 'the PEPS module arbitration along with high bus traffic leads to the BCM setting the door open switch virtual device availability (VDA) to unavailable.'

Mechanic-Grade Diagnostic Values

• LIN Bus Voltage Range (at rest) — expected: Approximately 12V (or 1V less than system/battery voltage). Failure: Voltage significantly lower than battery voltage, at 0V, or stuck high at exact battery voltage may indicate a short or open.
• LIN Bus Voltage Range (communicating) — expected: Toggling between approximately 1V (dominant) and 12V (recessive). Failure: A flat line at any voltage, or a signal that does not drop to ~1V, indicates a communication failure, short, or faulty module.
• LIN Bus Master Node Pull-up Resistor — expected: ~1 kΩ. Failure: Incorrect resistance can disrupt the entire LIN bus communication.
• LIN Bus Slave Node Pull-up Resistor — expected: ~30 kΩ (typically internal to the module). Failure: An incorrect internal resistance points to a faulty slave module (e.g., the PEPS module).

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > Body Control Module > Data Display — To monitor the live status of inputs to the BCM, such as door switch states. This can help verify if the BCM is receiving the correct physical signals before condemning the network.
• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > Keyless Entry Control Module > Data Display — To view data PIDs related to the PEPS module, such as key fob status and antenna signal strength, which can help rule out issues with the keyless entry hardware itself.
• GDS2 (GM Global Diagnostic System 2): Configuration / Reset Function > Transmission Service Fast Learn — While not directly for U1538, this function is an example of a critical reset procedure available in GDS2 that is required after certain hardware replacements. Similar programming/setup functions are required if the BCM or PEPS module is replaced.

Wiring & Ground Locations

• Body Control Module (BCM) — Located in the center console, behind the lower trim panel on the passenger side footwell.. The BCM is the master controller for the LIN bus that the PEPS module communicates on. A loose connector or damaged wiring at the BCM is a potential cause of communication codes.
• BCM Ground — A primary ground for the BCM is located at pin 9 of the X4 connector (black wire).. A poor ground connection at the BCM can cause a multitude of unpredictable electronic issues, including setting random communication codes like U1538.
• Passive Entry Passive Start (PEPS) Module — The PEPS module is typically located in the center console area, often near the BCM, to facilitate communication and antenna placement.. This is the slave module identified in TSB #16-NA-407. Checking its connector and wiring is a key diagnostic step if the software update does not resolve the issue.

Real Owner Repair Stories

• YouTube video by 'The Old Men Auto Repair' (Chevrolet Silverado (related GM platform)) — Power windows not working, codes U1534 and U1538 present and active.
  ❌ Tried (didn't work) Initial diagnosis pointed towards a faulty window motor or switch.
  ✅ What actually fixed it The technician located a corroded wire splice for the LIN bus under the carpet on the passenger side. Repairing the corroded splice by soldering in a new piece of wire and heat-shrinking it restored communication and fixed the issue.