B3935 on 2007-2011 Buick Lucerne: Security Light, No Start Causes & Fixes

What's Unique About the 2007-2011 Buick LUCERNE

The Buick Lucerne from this era, along with many other GM vehicles using the Passkey III+ system, is particularly sensitive to Radio Frequency (RF) interference. GM issued multiple Technical Service Bulletins (TSBs) highlighting that intermittent no-start conditions with code B3935 are frequently caused by other electronic devices on the owner's keychain. Unlike other vehicles where this code might immediately point to a faulty key or module, the primary diagnostic step for the Lucerne is to rule out these external interference sources first, as strongly advised by GM.

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)
• Engine starts and immediately stalls
• Security indicator light is illuminated or flashing on the dashboard
• "Service Theft Deterrent System" message on the driver information center (DIC)
• Car may start after waiting 10-15 minutes with the key in the 'ON' position (after a relearn cycle).

Most Likely Causes

1. Radio Frequency (RF) Interference 🔴 High Probability As documented in GM TSBs #PIC5650M and #PIC5650L, the Passkey III+ immobilizer system operates at a frequency (125 kHz) that is easily disrupted by other RFID devices like office key cards, gas station speed-pass fobs, or even other vehicle key fobs on the same ring. Aftermarket electronics like LED lights or USB chargers can also be a source of RFI.
   How to confirm: Remove the Buick ignition key from the keychain so it is completely isolated from all other keys, fobs, and cards. Attempt to start the vehicle with the lone key. If it starts reliably, interference is the cause. This is the first and most important diagnostic step.
   Typical fix: Keep the ignition key separate from other RFID-emitting devices. No parts are required.
   Est. part cost: $0
2. Worn or Damaged Ignition Key 🟡 Medium Probability → Shop Ignition Switch The internal transponder chip in the key can fail over time due to being dropped or from normal wear and tear. The key for this vehicle is a GM PK3+ type.
   How to confirm: Attempt to start the vehicle with a known-good spare key. If the spare key works consistently and the primary key does not, the primary key is faulty.
   Typical fix: A new key must be purchased, cut to match the original, and programmed to the vehicle by a locksmith or dealership with the appropriate tools. The vehicle itself is required for programming.
   Est. part cost: $40-$100
3. Faulty Ignition Lock Cylinder / Switch ⚪ Low Probability → Shop Ignition Switch The wires leading from the exciter coil (the ring around the ignition lock that reads the key) can break from the repeated stress of turning the key over many years. This is a known failure point on older GM vehicles. The cylinder assembly contains this reader coil.
   How to confirm: If neither the original nor the spare key works, and RF interference has been ruled out, the issue is likely with the reading coil in the ignition cylinder. This can be confirmed by testing the wiring for continuity or by observing related codes like B3055.
   Typical fix: Replace the ignition lock cylinder assembly. This part contains the new reading coil. The new cylinder will need to be programmed to the vehicle's existing keys. An ACDelco replacement part is GM 25832354 (also known as D1493F).
   Est. part cost: $60-$150

Rare But Worth Checking

• Failing Body Control Module (BCM): → Shop Body Control Module While rare, the BCM is the module responsible for the security handshake. If a new, correctly programmed key and ignition cylinder do not resolve the issue, the BCM itself may be faulty. Symptoms can also include other strange electrical issues like erratic lights, locks, or windows. A replacement BCM must be programmed to the car's VIN.
• BCM Software Glitch: In some cases, particularly on other GM models, a software update for the BCM has been released to fix intermittent no-start conditions with B3935. TSB PI1180A describes such an update for 2014-2015 GM trucks and SUVs. While not specific to the Lucerne, it establishes a precedent for software-related fixes.

Diagnosis Steps

1. Observe the dashboard for a flashing or solid security light when trying to start the car. This confirms a theft-deterrent issue.
2. CRITICAL FIRST STEP: Remove the Buick ignition key from your keychain. Ensure no other keys, fobs, or access cards are nearby. Try starting the engine with the isolated key. If it starts, the problem is RF interference. This solves the majority of cases.
3. If the car still won't start, try your spare key. If the spare key works, the original key is defective.
4. If neither key works, perform a 'Security Relearn Procedure'. Turn the key to the 'ON' position (do not crank) and wait for the security light to stop flashing and either turn off or go solid (approx. 10-15 minutes). Turn the key off for 10-20 seconds. Repeat this cycle two more times for a total of three 10-minute cycles. After the third cycle, turn the key off and then try to start the engine.
5. If the relearn procedure fails, the next most likely cause is the ignition lock cylinder's reader coil or its wiring. Inspect the wiring at the base of the steering column for breaks or damage.
6. If all else fails, professional diagnosis with a scan tool capable of reading BCM data is necessary to check the health of the Body Control Module and see if any software updates are available.

Parts You'll Likely Need

• Ignition Key with Transponder (PK3+) — This is needed if the chip inside the original key has failed.
  Trusted brands: ACDelco, Strattec
  OEM price range: $60-$100
  Aftermarket price range: $25-$50
• Ignition Lock Cylinder (OEM #25832354) — Replaces the key reader coil (exciter) which is a common point of failure due to broken wires inside the steering column. This part is often sold under ACDelco P/N D1493F as well.
  Trusted brands: ACDelco (GM Genuine), Dorman (e.g., 924-716)
  OEM price range: $120-$180
  Aftermarket price range: $60-$100
• Body Control Module (BCM) (OEM #15872388 (one of several, must match original)) — A last resort when all other components of the Passkey system check out. A replacement must be programmed with the vehicle's VIN.
  Trusted brands: ACDelco (GM Genuine), Remanufactured/Programmed units from specialty vendors
  OEM price range: $250-$400
  Aftermarket price range: $150-$250 (programmed)

Related Codes That Often Appear With This One

• B3055 — This code means 'No Transponder Modulation or No Transponder,' indicating the security module received no signal from the key at all. It often appears with B3935 when caused by RF interference or a broken wire in the ignition cylinder.
• B3060 — This code for 'Unprogrammed Transponder' can also appear alongside B3935, especially if there's an intermittent connection or severe interference causing the key data to be misread.

Technical Service Bulletins (TSBs) & Recalls

• PIC5650M: Diagnostic Tip - Security Light On Intermittently / No Crank/No Start Or Start Stall.
• PIC5650L: Diagnostic Tip - Security Light On Intermittently / No Crank/No Start Or Start Stall.
• PI1180A: Intermittent No Start, Security Lamp Illuminated, DTCs B3935 and B2955 Set (for other GM models, shows precedent for software fixes)

Platform-Specific Known Issues

• NHTSA TSB #PIC5650M & #PIC5650L: GM issued these bulletins to address intermittent no-crank/no-start conditions with code B3935. They explicitly warn technicians *not* to replace parts before investigating and questioning the customer about Radio Frequency Identification (RFID) devices on their keychain, as this is the most frequent cause.
• Ignition Key Recall: While for a different primary fault (unintended key rotation), a 2014 recall was issued for 2006-2011 Buick Lucernes related to the ignition key design. The fix involved a key insert to prevent heavy keychains from turning the ignition off. This highlights the sensitivity of the ignition system area on these models.