B3935 on 2013-2020 Buick Encore: Transponder Authentication Error & No-Start Fixes

What's Unique About the 2013-2020 Buick ENCORE

The Buick Encore from this generation, along with its platform-mates like the Chevy Trax and Sonic, is highly sensitive to Radio Frequency Interference (RFI). Manufacturer Technical Service Bulletins (TSBs) like PIC5650L and PIC5650M specifically warn technicians *not* to replace parts for this code initially. The primary cause is often external devices interfering with the 125 kHz signal between the key and the car. TSBs list common culprits as other key fobs, building access cards, toll passes, aftermarket LED lights, and even some USB phone chargers. This means that unlike many other codes that point to a failed part, B3935 on an Encore is frequently a 'ghost' code caused by its environment.

Diagnostic Flowchart

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

Symptoms You May Notice

• Engine will not crank (no-crank, no-start). [TSB #PIC5650M]
• Engine starts and immediately stalls. [TSB #PIC5650M]
• Security indicator light is on or flashing on the dashboard. [TSB #PIC5650M, 18]
• "Service Theft Deterrent System" message may appear on the driver information center.
• A single slow wipe of the windshield wipers upon a failed start attempt has been reported by some owners.

Most Likely Causes

1. Radio Frequency Interference (RFI) 🔴 High Probability As documented in multiple GM TSBs (including the PIC5650 series), the immobilizer system operates on a frequency (125 kHz) that is easily 'jammed' by other electronic devices. The TSBs explicitly list items like other car keys, toll passes, building access cards, aftermarket LED lights, and phone chargers as potential sources.
   How to confirm: Remove all other keys, key fobs, office access cards, toll passes, and any other electronic items from the keychain. Move cell phones and chargers away from the ignition area. Attempt to start the vehicle with only the single Encore key present.
   Typical fix: Isolate the Buick Encore key from all other electronic devices. This fix is typically free.
   Est. part cost: $0
2. Weak or Dead Key Fob Battery 🟡 Medium Probability → Shop Vehicle Battery A weak battery may not have enough power to properly transmit its signal back to the car's immobilizer antenna, especially if there is minor interference. The required battery is a CR2032.
   How to confirm: Try the spare key fob. If the spare key works reliably, the battery in the primary key is the likely culprit. For push-to-start models, placing the problematic fob in the designated transmitter pocket (in the front cup holder for non-GX models) may allow the car to start, which also points to a weak battery.
   Typical fix: Replace the CR2032 battery inside the key fob.
   Est. part cost: $5-$10
3. Faulty Key or Transponder Chip ⚪ Low Probability The transponder chip in the key can be damaged from being dropped or from internal failure, though this is less common than external factors.
   How to confirm: If removing RFI sources and replacing the battery doesn't work, but the spare key does, the original key is likely faulty. A locksmith or dealership can test the transponder's signal.
   Typical fix: The key must be replaced and programmed to the vehicle by a dealership or a qualified automotive locksmith.
   Est. part cost: $70-$250

Rare But Worth Checking

• Body Control Module (BCM) Software Glitch: → Shop Body Control Module A less common but documented issue involves a software glitch in the BCM that can cause it to improperly read the key's immobilizer information. GM released a software update under TSB PI1180A to address this. This typically presents as a no-crank, no-start condition where both codes B3935 and B2955 are set together.
• Faulty Immobilizer Antenna or Module: → Shop Antenna The antenna ring around the ignition switch (exciter coil) or the Theft Deterrent Module (TDM)/BCM itself can fail. However, TSBs specifically advise against replacing these parts unless all other possibilities, especially RFI, have been ruled out completely. [TSB #PIC5650L]

Diagnosis Steps

1. Check the dashboard for a solid or flashing security light. This confirms an active anti-theft issue.
2. Remove ALL other items from your keychain, including other car keys, house keys with RFID chips, and office access cards. TSB PIC5650M also lists aftermarket LED lights and USB chargers as potential sources of interference.
3. Move any cell phone chargers, garage door openers, or other electronic devices away from the center console and ignition area.
4. Attempt to start the car with the isolated Buick Encore key.
5. If the car still doesn't start, try using your spare key. If the spare key works, the problem is with the first key (likely its battery or transponder chip).
6. Replace the CR2032 battery in the non-working key fob.
7. For push-button start models, try placing the key fob in the dedicated transmitter slot and attempt to start the engine. For 2013-2020 Encore (non-GX models), this slot is inside the front cup holder.
8. If codes B3935 and B2955 are present together, consult a dealer about TSB PI1180A, which involves a BCM software update.
9. If none of the above steps work, the vehicle may require a security system relearn procedure or professional diagnosis with a scan tool to check the BCM/TDM and immobilizer antenna.

Parts You'll Likely Need

• Key Fob Battery (OEM #CR2032) — This is the second most common fix after removing RFI. A weak battery can't complete the 'challenge-response' with the car's security system.
  Trusted brands: Energizer, Duracell, Panasonic
  OEM price range: $5-$10
  Aftermarket price range: $2-$8
• Key Fob / Transmitter (OEM #13532383 (2017-2020), 13508417 (2017-2020 Smart Key), 22733524 (earlier models)) — If the internal transponder chip is damaged, the entire key fob assembly must be replaced and programmed to the vehicle.
  Trusted brands: ACDelco
  OEM price range: $100-$200
  Aftermarket price range: $50-$120

Related Codes That Often Appear With This One

• B3055 — This code relates to 'No Transponder Modulation or No Transponder,' indicating a problem in the initial communication with the key. It often appears with B3935 as part of the same security system fault. [TSB #PIC5650M, 25]
• B3060 — This code means 'Unprogrammed Transponder,' which can also be set during a failed authentication attempt. It's part of the same family of immobilizer codes. [TSB #PIC5650M, 25]
• B2955 — This code, related to the security system, is specifically mentioned in TSB PI1180A as appearing alongside B3935 when a BCM software update is required to fix a no-start condition.

Technical Service Bulletins (TSBs) & Recalls

• PIC5650M: Mentions B3935 in relation to intermittent no-crank/no-start or stall with the security light on. Lists numerous RFI sources like aftermarket LEDs and phone chargers.
• PIC5650L: The predecessor to PIC5650M, this TSB warns against replacing parts for B3935 and points to Radio Frequency Identification devices as a likely cause.
• PI1180A: Notes that a BCM software update is available for a no-start condition where B3935 and B2955 are set together.

Platform-Specific Known Issues

• This platform is highly susceptible to Radio Frequency Interference, as acknowledged by GM in multiple Technical Service Bulletins (PIC5650 series).
• A specific TSB (#PIC5650L) explicitly warns technicians not to replace any parts for this concern until RFI has been ruled out as the cause. [TSB #PIC5650L]
• The backup slot to start the car with a dead key fob is located in the front cup holder for push-to-start models of this generation.

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Immobilizer Learn — Used to program new or additional keys to the vehicle's Body Control Module (BCM). This is required when a key is replaced.
• GDS2 (GM Global Diagnostic System 2): Body Control Module Programming and Setup — Required after replacing the BCM itself, or when applying a software update like the one mentioned in TSB PI1180A to fix bugs related to codes B3935 and B2955.
• GDS2 (GM Global Diagnostic System 2): Data Display > Immobilizer Data — To monitor the live status of the immobilizer system. A technician can see if a key is recognized, if the transponder signal is valid, and the reason for the last failed start attempt, which is critical for diagnosing B3935.

Wiring & Ground Locations

• BCM (Body Control Module) — Located above the driver's side kick panel.. The BCM is the central module for the immobilizer system on this vehicle. It receives the key's transponder signal (via the immobilizer antenna) and decides whether to authorize the engine start. All related wiring and grounds connect back to this module.
• G218 — A critical BCM ground point located on the driver's side A-pillar, under the dash. On similar GM platforms, it's found in the upper left corner under the dash, sometimes near the speaker.. A poor connection at G218 is a known cause of numerous, seemingly unrelated electrical issues on GM vehicles, including no-start conditions, module communication errors, and flickering displays. The issue is often caused by sound-deadening material getting trapped under the ground terminal during assembly, leading to a poor connection. While not directly linked to B3935 in TSBs, a bad BCM ground can mimic module failure and should be inspected if other diagnostics fail.
• Immobilizer Antenna (Exciter Coil) — A ring-shaped antenna located around the ignition lock cylinder for keyed ignition models, or integrated near the push-to-start button or backup transmitter pocket for keyless models.. This antenna energizes the transponder chip in the key and receives its signal. A break in its wiring or an internal failure of the coil will prevent the BCM from ever seeing the key, leading to codes like B3055 and B3935.

Real Owner Repair Stories

• Reddit user in r/MechanicAdvice (2020 Buick Encore) — Key fob suddenly stopped being detected by the car. 'No remote detected' message displayed.
  ❌ Tried (didn't work) Replacing the CR2032 battery in the original key fob., Placing the fob in the backup slot (front cupholder) did not work., Purchasing a new compatible key fob and having it professionally programmed by a locksmith.
  ✅ What actually fixed it The issue was not resolved in the thread, but the diagnosis pointed conclusively to a vehicle-side problem. The locksmith confirmed the new fob was programmed and recognized, but the car itself would not accept the signal, indicating a likely failure of the car's immobilizer receiver module or related wiring, a rare but possible cause after all common fixes fail.

OEM Part Supersession History

• 13506665 → 13532383 — Standard part revision or manufacturer change for the key fob transmitter used on 2017-2020 Buick Encore models with remote start.
  Heads up: Both parts require programming by a dealer or qualified locksmith using GDS2. They are not interchangeable without programming.

Model Year Variations Within This Range

• 2013-2016: These earlier models used a flip-key design (e.g., Part #22733524). The immobilizer function is similar, but the key fob housing and battery replacement procedure are different from the later models.
• 2017-2020: Following the 2017 model year facelift, the Encore received a new key fob design, including both a standard key and a keyless access (push-button start) version (e.g., Part #13532383, 13508417). The battery replacement and internal electronics differ from the pre-2017 keys.