B2955 on 2015-2016 Buick Encore: Security Light and Immobilizer Fixes

What's Unique About the 2015-2016 Buick ENCORE

This particular vehicle and its platform mate, the Chevrolet Trax, are highly prone to setting a B2955 code due to a known software issue, not a physical part failure. General Motors issued Technical Service Bulletin #16-NA-128 acknowledging that the BCM can detect a "false circuit fault on the immobilizer antenna circuits". The TSB's official correction is to reprogram the BCM and explicitly states, "Do not replace any parts for this condition." This makes a software update the first and most important diagnostic step, unlike on other vehicles where a hardware fault would be the primary suspect.

Diagnostic Flowchart

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

Symptoms You May Notice

• Security light is on constantly or intermittently.
• "Service Theft Deterrent System" message on the Driver Information Center (DIC).
🎬 See how to clear the service anti-theft message
• Malfunction Indicator Light (MIL) / Check Engine Light may be on.
• Intermittent no-start or crank-no-start condition.

Most Likely Causes

1. Body Control Module (BCM) Software Requires Update 🔴 High Probability → Shop Body Control Module A specific software calibration issue causes the BCM to incorrectly flag a fault with the immobilizer antenna circuit. This is documented in GM Technical Service Bulletin #16-NA-128 for the 2015-2016 Encore and Trax.
   How to confirm: A GM dealer or a shop with a subscription to GM's Service Programming System (SPS) can check the BCM's current software calibration against the latest version. If the update specified in TSB #16-NA-128 has not been performed, this is the confirmed cause.
   Typical fix: Reprogram the Body Control Module (BCM) to the latest software version. The TSB explicitly states "Do not replace any parts for this condition." The technician must also ensure the vehicle's battery voltage is stable (between 12.6V and 15.5V) during the reprogramming process.
   Est. part cost: $0
2. Faulty Immobilizer Antenna ⚪ Low Probability → Shop Antenna While much less common than the software issue, the antenna (also called a transponder or exciter ring) that reads the key chip can fail. 🎬 Watch: How the Chevrolet immobilizer system works This should only be considered after the BCM has been updated.
   How to confirm: If the BCM software is up to date but the code persists, a technician can test the immobilizer antenna's circuit for proper resistance and voltage using a multimeter. An out-of-spec reading points to a failed antenna or wiring.
   Typical fix: Replace the immobilizer antenna, which is located around the ignition lock cylinder. 🎬 Watch: How to test and replace an immobilizer antenna
   Est. part cost: $40-$80
3. Wiring Harness Damage or Corrosion ⚪ Low Probability Damage to the wiring between the BCM and the immobilizer antenna can interrupt the signal. On some GM vehicles, a loose connector for the immobilizer control module has been identified as a cause. Spilled liquids in the console area have also been known to cause corrosion on related connectors on other GM models.
   How to confirm: Visually inspect the wiring harness and connectors between the BCM and the ignition lock cylinder for any signs of damage, chafing, loose connections, or corrosion. Perform a continuity test on the wires if no visual damage is found.
   Typical fix: Repair the damaged section of the wiring harness or clean/replace the corroded/loose connector.
   Est. part cost: $5-$25

Rare But Worth Checking

• Failing Body Control Module (BCM): → Shop Body Control Module If the BCM has been reprogrammed and both the wiring and immobilizer antenna test good, the BCM itself may have an internal hardware fault. This is the least likely cause and should only be considered after all other possibilities are exhausted.
• Aftermarket Remote Starter Interference: Poorly installed or failing aftermarket remote start systems can interfere with the factory immobilizer communications, causing intermittent B2955 codes. These systems often tap into the same wiring used by the immobilizer and can cause data corruption or signal loss.

Diagnosis Steps

1. Scan the vehicle's modules for trouble codes. Confirm B2955 is present.
2. Verify if Technical Service Bulletin #16-NA-128 has been performed. If not, this is the primary corrective action.
3. Using a GM-compatible scan tool (GDS2) and a stable power supply, have a qualified technician reprogram the Body Control Module (BCM) to the latest software calibration.
4. Clear the codes and test drive the vehicle. If the code does not return, the repair is complete.
5. If the code returns after the reprogram, perform a visual inspection of the wiring and connectors between the BCM and the immobilizer antenna for damage, corrosion, or looseness.
6. Test the immobilizer antenna circuit. Check for less than 30 ohms between the low reference circuit (terminal 1 at the antenna connector) and a known good ground.
7. Test for B+ voltage at the antenna connector (terminal 3). It should illuminate a test lamp for approximately three seconds when the ignition is turned ON.
8. If all circuits and components test normal but the code persists, suspect a hardware failure within the BCM itself.

Parts You'll Likely Need

• Body Control Module (BCM) Reprogramming — This is not a physical part, but a software update service. It is the most common and manufacturer-recommended fix for this specific code on this vehicle, as per TSB #16-NA-128.
  OEM price range: $125-$250
• Immobilizer Antenna (OEM #42461283) — If the BCM reprogram does not resolve the issue, the physical antenna that reads the key transponder is the next most likely part to have failed.
  Trusted brands: ACDelco (D1901F), Standard Motor Products
  OEM price range: $60-$100
  Aftermarket price range: $40-$80

Technical Service Bulletins (TSBs) & Recalls

• 16-NA-128 / SB-16-NA-128: "Security Light Comes On Intermittently, Malfunction Indicator Light (MIL) Illuminated, DTC B2955 Set" - This TSB is the primary source identifying a BCM software update as the fix for a false fault detection.

Platform-Specific Known Issues

• A GM Technical Service Bulletin (#16-NA-128) was issued for 2015-2016 Buick Encore and Chevrolet Trax models for this exact code. The bulletin states the cause is the BCM detecting a "false circuit fault" and the correction is to reprogram the BCM. It explicitly warns technicians: "Do not replace any parts for this condition."

Mechanic-Grade Diagnostic Values

• Immobilizer Antenna Low Reference Circuit to Ground — expected: Less than 30 Ω. Failure: A reading greater than 30 Ω indicates an open or high resistance in the ground circuit.
• Immobilizer Antenna B+ Circuit Voltage — expected: Test lamp illuminates for ~3 seconds when ignition is turned ON.. Failure: If the lamp does not illuminate, it indicates a short to ground or an open/high resistance in the power circuit.

Hidden / Shadow Codes Worth Checking

• B2955 00: The '00' symptom byte indicates a general 'Security Sensor Data Circuit Malfunction' without pointing to a more specific failure like short to ground or open circuit. This is consistent with the false fault reported in TSB 16-NA-128. (see via A professional GM-compatible scan tool like the GDS2 can display DTCs with their associated symptom bytes.)

Scan Tool Commands That Help

• GDS2 (Global Diagnostic System 2): Body Control Module Programming and Setup — This is the primary function required to execute the software update outlined in TSB 16-NA-128. It is performed through the Service Programming System (SPS) while connected to the vehicle.
• GDS2 (Global Diagnostic System 2): Immobilizer/Key Learning — This function is used after replacing a BCM or if keys need to be relearned. For B2955, this is typically not necessary unless other work has been performed, as the BCM reprogram does not erase key data.

Wiring & Ground Locations

• Body Control Module (BCM) — Located in the center console, directly behind the lower trim panel on the passenger side of the vehicle.. The BCM is the module that sets code B2955 and requires reprogramming. Technicians need to access its connectors to perform circuit tests if the reprogram does not fix the issue.
• Immobilizer Antenna (Transponder/Exciter Ring) — Located around the ignition lock cylinder, underneath the steering column covers.. This is the component that reads the key's transponder chip. Its wiring harness connector is the primary test point for diagnosing a physical circuit fault.
• G103 — A common GM ground point located at the left rear of the engine compartment on the cowl, often above the brake booster.. The BCM relies on a solid ground connection to function properly. While not the primary cause for this specific TSB-related issue, a poor ground at G103 can cause a wide range of erratic electrical problems, including BCM faults.

Real Owner Repair Stories

• YouTube user 'david turner' (2017 Buick Encore (similar platform/system)) — Theft deterrent system activated after the battery was completely drained and the vehicle was jump-started.
  ❌ Tried (didn't work) Scouring the internet for solutions, trying various resets.
  ✅ What actually fixed it The owner had only one key. They ordered a new key and had both the original and new key reprogrammed to the vehicle. This immediately cleared the theft deterrent system message.

OEM Part Supersession History

• 42461283 → No direct supersession found. This part number appears to be current for the specified model years. — N/A