B3935 on 2007-2010 GMC Sierra 3500: No-Start & Security Fault Causes

What's Unique About the 2007-2010 Gmc SIERRA 3500

On this generation of GMC Sierra (GMT900), the Pass-Key III+ immobilizer system is notoriously sensitive to Radio Frequency Interference (RFI). GM has issued multiple Technical Service Bulletins, including PIC5650K and PIC5650M, specifically warning technicians not to replace any parts for a B3935 code until RFI has been ruled out. TSB PIC5650M provides an extensive list of potential interference sources, including other vehicle keys, toll passes, aftermarket LED lights, cell phone chargers, and even decorative trim rings around the ignition cylinder. This is a well-documented quirk of the platform where the solution is often behavioral (isolating the key) rather than mechanical.

Diagnostic Flowchart

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

Symptoms You May Notice

• Intermittent no-crank or no-start condition.
• Engine starts and immediately stalls.
• Security light is illuminated or flashing on the instrument cluster.
• "Service Theft Deterrent System" message may appear on the Driver Information Center (DIC).

Most Likely Causes

1. Radio Frequency Interference (RFI) 🔴 High Probability The Pass-Key III+ system used in these trucks is sensitive to RFI operating in the 125 kHz range. GM TSBs PIC5650K and PIC5650M directly cite RFI as a primary cause. Sources include other key fobs, building access cards, toll passes, aftermarket LED lighting, USB phone chargers, and even decorative metal rings around the ignition.
   How to confirm: Remove all other keys, key fobs, and RFID-enabled cards from the keychain. Unplug any aftermarket accessories like phone chargers. Attempt to start the vehicle with only the single ignition key. If the vehicle starts, RFI was the cause.
   Typical fix: Keep the ignition key isolated from other electronic devices. No parts are required.
   Est. part cost: $0
2. Worn or Damaged Ignition Key 🟡 Medium Probability The transponder chip embedded in the plastic head of the key can be damaged from drops or simply fail over time, causing it to fail the authentication challenge.
   How to confirm: If removing RFI sources doesn't work, try starting the vehicle with a known-good spare key. If the spare key works consistently, the primary key is faulty.
   Typical fix: Replace the faulty key. A new key must be cut and then programmed to the vehicle using a 30-minute security relearn procedure.
   Est. part cost: $40-$100
3. Security System Communication Glitch ⚪ Low Probability Low battery voltage or random data errors, sometimes occurring after a jump-start or battery replacement, can cause the BCM/TDM to lose sync with the key, requiring a reset.
   How to confirm: After confirming the battery is fully charged and RFI/key issues are ruled out, perform the security relearn procedure. If the procedure works and the truck starts, a glitch was the likely cause.
   Typical fix: Perform the 30-Minute Security Relearn Procedure. This involves cycling the key to the 'ON' position for 10 minutes, three consecutive times. It is highly recommended to connect a battery charger during this process.
   Est. part cost: $0

Rare But Worth Checking

• Faulty Ignition Lock Cylinder / Theft Deterrent Module (TDM): The TDM, which includes the exciter ring (antenna) that reads the key, is part of the ignition lock cylinder housing located on the steering column. While less common, this component can fail, preventing any key from being read correctly. If neither the original nor a spare key works, and the relearn fails, this part is the next suspect. Replacement requires a subsequent relearn procedure.
• Poor BCM Ground Connection: These trucks can develop poor ground connections. A bad ground for the Body Control Module (BCM), often located near the driver's side instrument panel junction block, can cause a wide range of unpredictable electrical issues, including false security codes.
• Faulty Body Control Module (BCM): This is the least likely cause and should only be considered after all other possibilities, including wiring, have been thoroughly exhausted. A BCM failure is rare and expensive to fix.

Diagnosis Steps

1. Check the dashboard for an illuminated or flashing security light. This confirms the issue is with the anti-theft system.
2. Remove ALL other keys, fobs, and RFID cards from your keychain. Unplug any aftermarket chargers or accessories. Attempt to start the vehicle with the ignition key by itself. This is the most common fix.
3. If the problem persists, try your spare key. If the spare key works reliably, your primary key is faulty and needs replacement.
4. Ensure the vehicle's battery is fully charged (12.4V+). Low voltage can cause modules to malfunction. Connect a battery charger during further diagnostics.
5. Attempt the 30-Minute Security Relearn Procedure. 1. Turn the key to 'ON' (run position). 2. Attempt to start; the engine will not crank. 3. Leave the key in the 'ON' position for approximately 10 minutes, or until the security light turns OFF. 4. Turn the key OFF for 10 seconds. 5. Repeat steps 3 and 4 two more times (for a total of three 10-minute cycles). 6. After the third cycle, turn the key off, then attempt to start the engine. It should now start.
6. If the issue is still not resolved, inspect the wiring and connectors at the ignition lock cylinder and the Body Control Module (BCM) for any visible damage.
7. If all else fails, professional diagnosis with a GM-specific scan tool is needed to check the live data from the Theft Deterrent Module and check for specific symptom bytes.

Parts You'll Likely Need

• Transponder Ignition Key (PK3+) (OEM #Varies by VIN, but requires a PK3+ (Passkey III+) compatible key.) — If the original key's internal transponder chip has failed, a new key is the only solution. This is confirmed if a spare key works perfectly.
  Trusted brands: ACDelco, Strattec
  OEM price range: $60-$120
  Aftermarket price range: $25-$50
• Ignition Lock Cylinder with Passlock Sensor/TDM (OEM #ACDelco D1405D, ACDelco 15794826, Dorman 924-796 (kit with keys)) — If both the primary and spare keys fail to work and the relearn procedure is unsuccessful, the sensor that reads the key (part of the lock cylinder housing) may have failed.
  Trusted brands: ACDelco, Dorman
  OEM price range: $150-$250
  Aftermarket price range: $70-$150

Related Codes That Often Appear With This One

• B3055 — This code means 'No Transponder Key/Key Not Learned'. It often appears with B3935 because the system may first fail to read the key (B3055) before failing the authentication challenge (B3935). Both are cited together in TSB #PIC5650M and other service information.
• B3060 — This code points to an issue with the transponder antenna circuit (the exciter coil). It can appear with B3935 if the signal from the key is weak or corrupted by interference. It is also mentioned in TSB #PIC5650M.

Technical Service Bulletins (TSBs) & Recalls

• PIC5650M: Mentions B3935 in relation to intermittent no-crank/no-start/stall with the security light on, often alongside codes B3055 and B3060. Provides an extensive list of RFI sources.
• PIC5650K: Advises against replacing parts for B3935 and to first investigate Radio Frequency Interference from devices on the customer's keychain.
• PIE0232: An engineering information bulletin from 2012 requesting field data on low-mileage 2013 Silverado/Sierra trucks with B3935, B3055, or B3060, showing GM was actively investigating the root cause.

Platform-Specific Known Issues

• GM Technical Service Bulletin #PIC5650K explicitly states for intermittent no-start conditions with code B3935, technicians should not replace any parts and should first inquire about Radio Frequency Identification devices the customer may be using.
• GM Technical Service Bulletin #PIC5650M expands on RFI issues, listing aftermarket LED lighting, cell phone chargers, USB power banks, and even decorative 'Bedazzle Trim Rings' around the ignition as a potential cause of interference that can set code B3935.

Hidden / Shadow Codes Worth Checking

• B3935 57: The '57' is a GM-specific symptom byte for 'Transponder Authentication Error'. It confirms that the system successfully read the key's presence but the cryptographic challenge/response calculation failed. This points specifically to a key transponder fault or strong RFI, rather than an unknown key or antenna issue. (see via A professional GM-specific scan tool like a Tech 2 or GDS2 is required to view symptom bytes.)

Scan Tool Commands That Help

• GM Tech2 / GDS2: Module Diagnostics > TDM/BCM > Data Display — Use this to monitor live data from the Theft Deterrent Module (TDM). A technician can see the state of the security system, whether a key is recognized, and the status of the authentication process. This is the first step in electronic diagnosis after retrieving codes.
• GM Tech2 / GDS2: Vehicle Theft Deterrent (VTD) Learn / Add/Replace Keys — This function is used to program new keys to the vehicle's immobilizer system. It is required after replacing a key or the BCM. The scan tool provides a guided procedure that often incorporates the 30-minute security wait time.
• GM Tech2 / GDS2: BCM/TDM Module Setup — This function is required after replacing the Body Control Module (BCM) or Theft Deterrent Module (TDM). It syncs the new module to the vehicle's VIN and other existing control units before key learning can be performed.

Wiring & Ground Locations

• BCM Ground Path (2007 Models) — For 2007 models, the BCM ground path runs through the Left Instrument Panel Junction Block.. GM issued a specific bulletin (07-08-47-004D) warning that removing this junction block without first disconnecting the negative battery terminal can damage the BCM internally, leading to various electrical faults, including potential security system errors.
• G303 / G304 — G303 is located on the lower left 'B' pillar, and G304 is on the lower right 'B' pillar (for extended/crew cab models).. These are major body and chassis ground points. Corrosion or looseness at these locations can cause intermittent electrical issues for various systems that share these grounds, potentially affecting BCM operation and leading to false security codes.

Real Owner Repair Stories

• Camaro5 Forum User (similar Passkey III+ system) (2012 Chevrolet Camaro SS) — No crank, "Service Theft Deterrent System" message on DIC. Remote start would work, but the engine would die when the key was inserted and turned.
  ❌ Tried (didn't work) Disconnecting and reconnecting the battery., A 30-minute key relearn procedure with the original, faulty key.
  ✅ What actually fixed it The transponder in the original key had failed. The owner had a new, standard (non-switchblade) key cut and then successfully performed the 30-minute relearn procedure with the new key, which resolved the B3935 code and allowed the car to start.
• Technician reports on various GM Trucks/SUVs (2007-2014 GM Trucks/SUVs) — Intermittent no-crank, no-start with security light on and codes B3935 and B3055 stored.
  ❌ Tried (didn't work) Replacing the key., Performing the 30-minute relearn procedure multiple times.
  ✅ What actually fixed it The final fix was the replacement of the ignition lock cylinder assembly (e.g., ACDelco D1432D). The exciter coil (antenna) within the original cylinder had developed an intermittent open circuit, preventing it from reliably powering and reading the key's transponder chip, even with a new key.

Model Year Variations Within This Range

• 2007 only: According to GM bulletin 07-08-47-004D, the BCM ground path for 2007 models specifically runs through the Left Instrument Panel Junction Block. Servicing this junction block without disconnecting the battery can lead to BCM damage.