B3935 on 2007 Buick Rendezvous: Security Fault, No-Start Causes and Fixes

What's Unique About the 2007-2007 Buick RENDEZVOUS

The 2007 Buick Rendezvous uses GM's Passkey III immobilizer system, which is known to be highly sensitive. General Motors issued multiple Technical Service Bulletins (TSBs), including PIC5650K and PIC5650M, specifically addressing this issue across many models. These bulletins strongly advise technicians *not* to replace any parts for this code until Radio Frequency Interference (RFI) has been completely ruled out, as it is the most common cause of the problem on this platform.

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 or start.
• Engine starts briefly and then immediately stalls.
• Security warning light is illuminated or flashing on the dashboard.
• Odometer may display an 'error' message if the security fault is severe enough to disrupt communication on the data bus.

Most Likely Causes

1. Radio Frequency Interference (RFI) 🔴 High Probability As documented in GM TSBs PIC5650K and PIC5650M, the Passkey III system is sensitive to interference from other RFID devices. TSB PIC5650C provides a detailed list including: other vehicle keys, office access cards, gas station speed passes, aftermarket LED lights, and various USB-powered devices like phone chargers and power banks.
   How to confirm: Remove the Rendezvous key from the keychain so it is by itself. Unplug all aftermarket devices from the 12V power outlets. If the vehicle starts consistently, RFI was the cause.
   Typical fix: Isolate the ignition key from other electronic devices. Remove or replace any low-quality aftermarket accessories that are generating interference. 🎬 See how radio interference can disrupt your vehicle's security system.
   Est. part cost: $0
2. Faulty or Weak Ignition Key 🟡 Medium Probability → Shop Ignition Switch The transponder chip embedded in the key head can be damaged if the key is dropped or can simply fail with age, preventing it from correctly responding to the security challenge.
   How to confirm: Attempt to start the vehicle with a known-good spare key. If the spare key works reliably, the original key is faulty.
   Typical fix: Replace the faulty key. The new key must be cut and programmed to the vehicle by a locksmith or dealer.
   Est. part cost: $75-$250
3. Security System Requires Relearn 🟡 Medium Probability After a battery disconnect, a dead battery, or a voltage spike, the BCM can lose its synchronization with the key, requiring a manual reset.
   How to confirm: Attempt the 30-minute security relearn procedure. 🎬 Watch this video to see the step-by-step relearn process. If the procedure completes and the vehicle starts, this was the issue.
   Typical fix: Perform the 30-minute security relearn procedure. 1) Turn the key to 'ON' (do not start) and wait for the security light to turn off (approx. 10-12 minutes). 2) Turn the key 'OFF' for 5-10 seconds. 3) Repeat steps 1 and 2 two more times for a total of three cycles. After the third cycle, turn the key off, then the vehicle should start.
   Est. part cost: $0
4. Faulty Ignition Lock Cylinder / Transponder Reader ⚪ Low Probability → Shop Ignition Switch The exciter coil (antenna) that energizes and reads the key's transponder is part of the ignition lock cylinder assembly. 🎬 Watch a professional walkthrough of the lock cylinder replacement. This component can fail electrically over time, or the wiring to it can become damaged.
   How to confirm: If RFI is ruled out, a spare key doesn't work, and the relearn procedure fails, the lock cylinder is the next likely suspect. This requires testing the circuit with a multimeter or wiggling the key in the ignition to see if the symptom can be reproduced. This is best left to a professional.
   Typical fix: Replace the ignition lock cylinder assembly. This part often comes from the OEM as a unit. After replacement, a security relearn procedure is required.
   Est. part cost: $70-$250

Rare But Worth Checking

• Failing Body Control Module (BCM): → Shop Body Control Module This is the least likely cause. The BCM is the computer that manages the security system. It should only be considered after all other possibilities, including wiring, have been thoroughly exhausted. On related platforms, corrosion in the BCM harness connectors has been found to cause this code. Replacement is expensive and requires professional programming.

Diagnosis Steps

1. Verify the security light is on or flashing when you try to start the vehicle.
2. Scan for all DTCs in the Body Control Module (BCM). Note any accompanying codes like B3055 or B3060.
3. Perform a thorough inspection for RFI sources, as per TSB #PIC5650K/M. Remove all other keys, fobs, and RFID cards from the keychain. Unplug ALL aftermarket devices (chargers, dash cams, USB power banks, LED lights, etc.).
4. Attempt to start the vehicle with the ignition key completely isolated. If it starts, the issue is RFI.
5. If the issue persists, attempt to start the vehicle with a known-good spare key. If it starts, the original key is faulty.
6. If a spare key is unavailable or also fails, perform the 30-minute security relearn procedure. Ensure the battery is fully charged first.
7. If the relearn fails, inspect the wiring and connector at the ignition lock cylinder for damage. This requires removing the steering column shrouds.
8. If all previous steps fail, the issue likely lies with the ignition lock cylinder or, in rare cases, the BCM itself, requiring professional diagnosis.

Parts You'll Likely Need

• No Parts Needed — Per GM TSBs PIC5650K and PIC5650M, the most common cause is Radio Frequency Interference, which is resolved by removing the interfering device, not by replacing a vehicle part.
  OEM price range: $0
  Aftermarket price range: $0
• Ignition Key — If the transponder chip inside the key has failed, the key itself must be replaced. This is the most common hardware failure after RFI is ruled out.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $100-$200
  Aftermarket price range: $50-$120
• Ignition Lock Cylinder (OEM #15815961) — This assembly contains the transponder antenna (exciter coil). If the coil fails, it cannot read the key, causing this code. This is the next most likely hardware failure. The GM part number is 15815961, which replaces the older part number 12472980.
  Trusted brands: ACDelco (D1469G), Dorman (924-716), Standard Motor Products (US-312L)
  OEM price range: $150-$250
  Aftermarket price range: $70-$180

Related Codes That Often Appear With This One

• B3055 — Stands for 'No Transponder Modulation'. It often appears with B3935 as part of the same security event, especially when RFI or a faulty key is the cause.
• B3060 — Indicates an 'Unprogrammed Transponder'. It is frequently logged alongside B3935 if communication is corrupted by interference or if the key is failing.
• C0750, C0755, C0760, C0765, C0775 — These are Tire Pressure Monitoring System (TPMS) codes. TSB #PIC5650M notes they can appear with security codes due to widespread radio frequency interference affecting both the immobilizer (125 kHz) and TPMS systems (315 MHz), indicating a noisy electrical environment.

Technical Service Bulletins (TSBs) & Recalls

• PIC5650M: Addresses an intermittent no crank, no start, or start stall concern with the security light coming on, listing B3935 and associated codes like B3055, B3060, and C0750-C0775.
• PIC5650K: Explicitly states that technicians should not replace any parts for this concern and should first investigate if the customer uses any Radio Frequency Identification devices.

Platform-Specific Known Issues

• A GM Technical Service Bulletin (TSB #PIC5650K/M) explicitly warns about intermittent no-starts on this vehicle caused by a wide range of Radio Frequency Identification devices and aftermarket electronics, not just items on the keychain. It advises against replacing any parts until RFI is ruled out.
• The Passkey III system used in the Rendezvous is known for this specific failure mode across the entire GM lineup from this era, including platform mates like the Pontiac Aztek and other models like the Chevrolet Equinox.

Hidden / Shadow Codes Worth Checking

• B3935 57: Symptom byte for 'Transponder Authentication Error'. It confirms the BCM recognized a learned key, but the cryptographic challenge/response calculation failed. This points strongly toward a faulty key chip or RFI rather than an unprogrammed key. (see via GM Tech 2, GDS2, or other professional scan tool capable of reading manufacturer-specific symptom bytes.)
• B3935 3A: Symptom byte for 'Incorrect Transponder Key'. This indicates the key's transponder ID itself was not on the BCM's list of learned keys, which could happen with a new, unprogrammed key or a severely corrupted signal. (see via GM Tech 2, GDS2, or other professional scan tool.)

Scan Tool Commands That Help

• Tech 2 / GDS2: Vehicle Theft Deterrent (VTD) Learn — This function is used to initiate the security relearn procedure after replacing a key or the BCM. It guides the technician through the process required for the system to learn new component IDs.
• Tech 2 / GDS2: Data Bus Diagnostic Tool / View All Modules — Used to verify which modules are communicating on the Class 2 data bus. If the BCM or TDM is not responding, it points to a power, ground, or communication line issue rather than a simple key authentication failure.

Wiring & Ground Locations

• Body Control Module (BCM) — Located in the center console, above the fuse block.. The BCM is the central computer for the Passkey III system. It receives the key data from the reader, performs the security calculations, and sends the fuel-enable password to the ECM. All relevant wiring terminates here.
• G201 — A primary body ground point located on the left side of the dash, on the underside of the cross-car beam.. This is a critical ground for the BCM. A loose or corroded connection at G201 can cause intermittent BCM power loss, leading to a wide range of electrical issues, including security faults like B3935.
• Theft Deterrent Module (TDM) / Exciter Coil — Located in the steering column, as part of the ignition switch assembly. The coil is a ring around the ignition lock cylinder.. This component energizes the transponder in the key and reads its signal. The wiring for this module runs down the steering column and is susceptible to damage from tilt-wheel adjustments or other repairs, causing a direct failure to read the key.
• Splice Pack SP205 — Located on the left side of the dash behind the access panel.. This is a junction point for the Class 2 Serial Data line. Corrosion or a poor connection within this splice pack can disrupt communication between the BCM, PCM, and other modules, potentially causing security errors.

Real Owner Repair Stories

• Chevy HHR Network forum user (2007 Chevrolet HHR (uses same Passkey III system)) — No start, security light remains on constantly, 30-minute relearn procedure fails (security light never turns off during the 10-minute cycles).
  ❌ Tried (didn't work) Performing the standard 30-minute relearn procedure multiple times., Disconnecting the battery to reset the computer.
  ✅ What actually fixed it The original problem was caused by a botched theft attempt where the ignition wiring was cut. The user repaired the wiring with butt splices, but the relearn still failed. The forum consensus pointed to the splices potentially adding resistance to the sensitive Passkey circuit, or a damaged BCM/TDM from the initial wiring damage, requiring a professional scan tool (Tech 2) to diagnose further communication issues.

OEM Part Supersession History

• 12472980 → 15815961 — Part revision or manufacturer change for the Ignition Lock Cylinder assembly.
  Heads up: No incompatibility is noted; 15815961 is the direct replacement for 12472980. After replacement, a security relearn procedure is required.