B3935 on 2007-2014 Chevrolet Equinox: No Start, Security Light, and Fixes

What's Unique About the 2007-2014 Chevrolet EQUINOX

For this generation of Chevrolet Equinox and its platform mates (like the Pontiac Torrent and GMC Terrain), the B3935 code is frequently caused by external factors rather than a failed part on the vehicle. General Motors has issued multiple, evolving Technical Service Bulletins (TSBs), like PIC5650M, warning technicians not to replace any parts until they have ruled out Radio Frequency Interference (RFI). 🎬 See how to fix 'No Fob Detected' errors caused by interference. This interference can come from other car keys, building access cards, aftermarket phone chargers, or even aftermarket LED interior lights on the same keychain or inside the car, making a simple fix possible without any tools or expense.

Diagnostic Flowchart

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

Generation note: The 2007-2014 range covers the end of the first generation (2007-2009) and the beginning of the second generation (2010-2014) Equinox. The immobilizer system principles (Pass-Key III+) are similar, but the control module architecture changed. First-generation models use a separate Theft Deterrent Module (TDM), while second-generation models integrate these functions into the Body Control Module (BCM). The TSBs regarding radio frequency interference apply across both generations within this year range.

Symptoms You May Notice

• Engine will not crank or start.
• Engine starts and immediately stalls.
• Security indicator light (a car with a lock symbol) is on or flashing on the dashboard.
• A "Service Theft Deterrent System" message may appear on the Driver Information Center (DIC).

Most Likely Causes

1. Radio Frequency Interference (RFI) 🔴 High Probability As documented in GM TSBs PIC5650M and its predecessors, the vehicle's security system is highly sensitive to external radio signals. The bulletins explicitly state this is the most likely cause and to investigate it before replacing any parts.
   How to confirm: Remove the Equinox key from your keychain so it is by itself. Take all other car keys, fobs, office access cards, and aftermarket electronics (like phone chargers, dash cams, or even LED bulbs) out of the vehicle. Try to start the car with only the single, isolated key present.
   Typical fix: Isolate the vehicle key from other RFID-emitting devices. No parts are replaced.
   Est. part cost: $0
2. Defective Ignition Key 🟡 Medium Probability The transponder chip embedded in the key head can be damaged from being dropped, exposed to moisture, or can fail electronically over time. Owners on forums report keys suddenly failing.
   How to confirm: After ruling out RFI, try starting the vehicle with a known-good spare key. If the spare key works reliably, the primary key is faulty. A locksmith or dealer can also test the key's transponder signal.
   Typical fix: Replace the faulty key. A new key must be cut and then programmed to the vehicle by a dealer or an automotive locksmith using the 30-minute relearn procedure.
   Est. part cost: $75-$250
3. Faulty Body Control Module (BCM) Software ⚪ Low Probability GM released TSB PI1180A for some 2014 models indicating that a software glitch in the BCM could cause a no-start with B3935 and B2955. This specifically applies to the end of this vehicle range.
   How to confirm: This requires a dealer or qualified shop to check for available software updates for the BCM using the GM Service Programming System (SPS). The issue is confirmed if both B3935 and B2955 are present.
   Typical fix: Reprogram the BCM with the latest software calibration. This is a 0.5-hour labor operation per the TSB.
   Est. part cost: $0 (if under warranty) or 0.5-1 hour labor charge
4. Failed Theft Deterrent Module (TDM) or Antenna Coil ⚪ Low Probability The module itself (TDM on 2007-2009, BCM on 2010-2014) or the antenna ring (exciter coil) around the ignition lock cylinder that reads the key can fail electronically. The wiring and connector between the antenna and the module can also become damaged or loose.
   How to confirm: If RFI is ruled out and a spare key also fails to start the vehicle, a technician will need to use a scan tool to test the TDM/BCM and its circuits. This may involve checking for a signal from the antenna coil and verifying power and ground to the module.
   Typical fix: Replace the faulty module or antenna coil, followed by a security relearn procedure.
   Est. part cost: $150-$400

Rare But Worth Checking

• Worn Ignition Lock Cylinder/Switch: A mechanically worn ignition switch can cause poor contact for the antenna coil, leading to intermittent reading of the key transponder.
• Low Vehicle Battery Voltage: A weak or dying battery can cause various electronic modules, including the TDM and BCM, to behave erratically during startup, potentially triggering a false security event. A fully charged battery is required to perform the 30-minute relearn procedure.
• Damaged Wiring: A broken wire between the ignition lock cylinder's antenna and the TDM/BCM can prevent the key from being read, causing this code.

Diagnosis Steps

1. Check for other trouble codes in all modules to get a complete picture of the fault.
2. Isolate the ignition key. Remove it from the keychain and ensure no other keys, fobs, or access cards are nearby.
3. Remove any aftermarket 12V or USB chargers, dash cams, and aftermarket LED bulbs from the vehicle's power outlets and light sockets.
4. Attempt to start the vehicle with the isolated key. If it starts, the issue is RFI. Re-introduce items one by one to find the culprit.
5. If the vehicle still doesn't start, try a known-good spare key. If the spare key works, the original key is faulty and needs replacement.
6. If the spare key also fails, check the vehicle's battery to ensure it is fully charged and providing stable voltage. A weak battery can cause security system issues and will prevent a successful relearn procedure.
7. Perform a security system relearn procedure. This typically involves turning the key to the 'ON' position (without starting) for 10-11 minutes until the security light turns off, then turning the key 'OFF' for 5-30 seconds. Repeat this cycle two more times for a total of three cycles (approx. 30-33 minutes). After the third cycle, turn the key off, then attempt to start the engine.
8. If the relearn procedure fails, professional diagnosis is needed to test the Theft Deterrent Module/BCM, its antenna coil, and the associated wiring for continuity and proper signals.

Parts You'll Likely Need

• Transponder Ignition Key (OEM #GM B111-PT (Circle Plus key, for 2007-2010 models) or GM B119-PT / HU100 blade style (for 2010-2014 models)) — If the transponder chip in the original key has failed, a new key is the only solution. This is a common point of failure after ruling out interference. A user with a similar GM system fixed a B3935 code with a new key and relearn.
  Trusted brands: ACDelco, Strattec, ilco
  OEM price range: $60-$120
  Aftermarket price range: $25-$50

Related Codes That Often Appear With This One

• B3055 — Relates to a problem with the transponder key itself (No Transponder Key Programmed). Often set alongside B3935 during a security system fault. [Bulletin #PIC5650M, #PIE0232]
• B3060 — Indicates an issue with the transponder antenna circuit (the reader around the ignition), also known as the exciter coil. It's part of the same system and can be triggered during a key authentication failure. [Bulletin #PIC5650M, #PIE0232]
• B2955 — This code (Security Sensor Data Circuit Malfunction), in conjunction with B3935 on 2014 models, specifically points to a BCM software issue that requires a dealer re-flash, as noted in TSB PI1180A.

Technical Service Bulletins (TSBs) & Recalls

• PIC5650M: Mentions B3935 in relation to intermittent no-crank/no-start/stall with the security light on, and strongly advises checking for RFI from aftermarket devices before replacing parts.
• PIC5650L: An earlier version of the above TSB, specifically advises not to replace parts for B3935 and to ask about Radio Frequency Identification devices the customer may be using. [NHTSA Record]
• PI1180A: Addresses a no-start condition with B3935 and B2955 on some 2014 models, which can be fixed by reprogramming the BCM.
• PIE0232: An engineering information request from 2012 showing GM investigating the root cause of B3055, B3060, and B3935 on new vehicles, again highlighting the sensitivity to RFI.

Platform-Specific Known Issues

• As per TSBs PIC5650M and PIC5650L, these vehicles are highly susceptible to Radio Frequency Interference causing intermittent no-start conditions with code B3935. The bulletins explicitly advise against replacing parts before investigating RFI from items on the customer's keychain or inside the vehicle.
• A user on the Chevy Equinox Forum reported a complete electrical cutout that was temporarily fixed by moving the battery cover assembly, suggesting a potential issue with the main fuse block connections on some vehicles.

Mechanic-Grade Diagnostic Values

• Scan Tool Immobilizer Data PID — expected: The 'Immobilizer Key Status' should read 'OK' or 'Valid Key'.. Failure: Parameter displays 'No Key Detected', 'Invalid Key', or similar negative status when a known-good key is in the ignition.
• Transponder Exciter Coil Resistance — expected: While a specific Ohm value is not published in general service data, a reading should be taken for comparison against a known-good part. An open circuit (infinite resistance) or short to ground (zero resistance) indicates a failed coil.. Failure: Infinite resistance (open loop) or zero resistance (short circuit).

Scan Tool Commands That Help

• GDS2 / Tech 2: Module Diagnostics > BCM (or TDM) > Data Display > Immobilizer Data — Use this to view live data from the security system, such as key status, number of programmed keys, and the reason for the last security event. This is the first step in electronic diagnosis after checking for codes.
• SPS (Service Programming System): BCM Body Control Module - Programming — This function is required to update the BCM software, which is the specific fix for 2014 models that have both B3935 and B2955 set, per TSB PI1180A.
• SPS (Service Programming System): IMMO (Immobilizer) Learn — This function is required after replacing the BCM (or TDM) or when programming new keys. It guides the technician through the security relearn process.

Wiring & Ground Locations

• BCM (2010-2014) — Under the driver's side of the dashboard.. On second-generation models, the BCM contains the theft deterrent logic. All wiring from the ignition cylinder's antenna coil terminates here. Poor connections or a faulty module are a primary focus of diagnosis.
• TDM (2007-2009) — Typically located in the center of the dash, often behind the HVAC control module or radio.. On first-generation models, this is the standalone module for the Pass-Key III+ system. It is the central point for testing.
• BCM Connector C3 (2010-2014) — Light Green 25-pin plug at the BCM.. This connector contains critical wiring for the ignition state. For example, the Ignition 1 circuit is a Pink wire at Pin 6, and the Accessory circuit is a Brown wire at Pin 5.
• G203 (2007-2009) — Located on the I/P (Instrument Panel) fuse block at the lower center of the dash.. A poor ground connection at this point can cause erratic behavior in multiple modules controlled by the BCM/TDM, potentially leading to false security events.

Real Owner Repair Stories

• Camaro5 Forum User (GM Vehicle with Pass-Key III+ system (Camaro)) — No crank, no start, with 'Service Theft Deterrent System' message on the DIC and trouble code B3935 stored.
  ❌ Tried (didn't work) Initial diagnosis was uncertain between a bad key or a bad module.
  ✅ What actually fixed it A locksmith cut a new, inexpensive, standard transponder key (not a switchblade remote key). The owner then successfully performed the 30-minute key relearn procedure themselves. The car started and ran normally afterward.

"I Checked Everything" — The Actual Cause

• The equivalent for this electronic issue is 'all parts test good, but the problem persists'. The most common scenario is a technician replacing the key, the ignition lock cylinder, and even the TDM/BCM, only for the intermittent no-start to return. The actual cause, as highlighted by GM's own TSBs (PIC5650M/L), is often Radio Frequency Interference (RFI) from another device on the owner's keychain or a cheap aftermarket charger plugged into the car. The standard diagnostic procedure often overlooks a thorough RFI investigation, leading to unnecessary parts replacement.

Model Year Variations Within This Range

• 2007-2009: These first-generation models use a separate, standalone Theft Deterrent Module (TDM) to manage the Pass-Key III+ system. Diagnosis focuses on this module and its dedicated wiring.
• 2010-2014: These second-generation models integrate the theft deterrent functions directly into the Body Control Module (BCM). There is no separate TDM. Diagnosis focuses on the BCM, its programming, and its connections.
• 2014: A specific software issue in the BCM can cause B3935 along with B2955, requiring a dealer-level software re-flash per TSB PI1180A, a problem not documented for earlier years.