B3935 on 2022-2026 Chevrolet Express: Security Light & No-Start Causes

What's Unique About the 2022-2026 Chevrolet EXPRESS

The Chevrolet Express and its identical platform-mate, the GMC Savana, use a Passkey III+ (PK3+) immobilizer system that is notoriously sensitive to Radio Frequency Interference (RFI). The immobilizer system operates at a frequency of 125 kHz, and other devices that operate in or near this range can cause interference. GM has issued multiple Technical Service Bulletins (like PIC5650L and PIC5650M) specifically warning technicians *not* to replace parts for this code until RFI from aftermarket devices (phone chargers, LED lights) and other items on the keychain (other car keys, access cards) has been ruled out. This makes external factors, rather than a failed part on the van itself, the most common cause.

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 indicator light on the dashboard is illuminated or flashing.
• Message on the driver information center like "No Fob Detected" or "Service Theft Deterrent System".
• Remote Keyless Entry (RKE) has poor or no range.

Most Likely Causes

1. Radio Frequency Interference (RFI) 🔴 High Probability The GM Passkey III+ system's 125 kHz frequency is easily 'jammed' by other electronic devices. This is the most common cause, as stated in numerous GM TSBs. Common culprits include other vehicle keys, building access cards, toll passes, aftermarket LED lights, and cheap USB phone chargers.
   How to confirm: Remove the Express ignition key from the keychain so it is completely isolated. Unplug all aftermarket devices like phone chargers, dash cams, and GPS units. If the vehicle starts consistently, RFI was the cause.
   Typical fix: Keep the ignition key separate from other keys, fobs, and RFID cards (toll passes, building access cards). Avoid using low-quality aftermarket electronics that plug into the vehicle's power outlets.
   Est. part cost: $0
2. Faulty or Damaged Ignition Key 🟡 Medium Probability The Philips ID 46 (Circle-Plus) transponder chip embedded in the key can be damaged by drops, water, or simply fail with age, preventing it from completing the security handshake. The battery in the key is for remote functions and is not related to the transponder chip.
   How to confirm: After ruling out RFI, try starting the vehicle with a known-good spare key. If the spare key works reliably and the primary key does not, the primary key is faulty.
   Typical fix: The faulty key must be replaced. A new key will need to be cut and programmed to the vehicle by an automotive locksmith or a dealership. A manual 30-minute relearn procedure may also be possible.
   Est. part cost: $75-$250
3. Low Vehicle Battery Voltage ⚪ Low Probability Low system voltage during startup can cause various electronic modules, including the BCM, to malfunction and set erroneous security codes. This can also happen after a jump start or battery replacement.
   How to confirm: Test the 12V battery with a multimeter or a battery tester. A healthy, fully charged battery should read approximately 12.6 volts with the engine off. A load test is recommended to confirm battery health.
   Typical fix: Recharge or replace the vehicle's 12V battery.
   Est. part cost: $150-$350

Rare But Worth Checking

• Faulty Immobilizer Antenna (Exciter Coil): This is the ring around the ignition lock cylinder that powers the key's transponder. While not a common failure, a break in its wiring or an internal fault can prevent it from energizing the key, leading to this code.
• Faulty Body Control Module (BCM): In rare cases, the BCM itself can fail. This is an expensive last resort and should only be considered after all other possibilities, including wiring issues, have been exhausted. Sometimes a software re-flash by the dealer can resolve the issue without replacing the module.
• Blown Fuse: An owner of a 2015 Express 4500 with a no-crank/no-start and anti-theft light found a blown 2-amp fuse (F22) was the ultimate cause. Checking relevant fuses in the under-hood block is a worthwhile step.

Diagnosis Steps

1. Verify the security light is on or flashing when the no-start condition occurs.
2. Isolate the ignition key. Remove it from any keychain with other keys, fobs, or RFID cards and try to start the vehicle. This is the most critical first step.
3. Unplug all aftermarket accessories from the 12V power outlets (phone chargers, dash cams, LED lights, etc.) and try to start the vehicle again.
4. If the issue persists, attempt to start the vehicle with a known-good spare key. If the spare key works, the original key is faulty.
5. Check the vehicle's 12V battery to ensure it is fully charged (12.6V+) and in good health.
6. Inspect fuses related to the anti-theft system or BCM in the under-hood fuse block.
7. If the above steps do not resolve the issue, the vehicle requires professional diagnosis with a scan tool (like a GM Tech 2 or GDS2) capable of reading GM body codes to inspect the immobilizer data stream and test the components of the security system.

Parts You'll Likely Need

• Ignition Key with Transponder (OEM #GM 23300334) — If RFI is not the cause, the transponder chip in the key is the next most likely component to have failed. The key uses a Philips ID 46 (Circle-Plus) chip.
  Trusted brands: ACDelco, Strattec
  OEM price range: $100-$200
  Aftermarket price range: $50-$120

Related Codes That Often Appear With This One

• B3055 — This code means 'No Transponder Modulation or No Transponder,' indicating the BCM couldn't detect a key at all. It often appears with B3935 when RFI is strong enough to completely block the signal or the key is completely dead.
• B3060 — This code means 'Unprogrammed Transponder.' It can be set with B3935 if interference corrupts the signal, making it appear as if an unprogrammed key is being used.
• C0750, C0755, C0760, C0765, C0775 — These are Tire Pressure Monitor (TPM) codes. TSB PIC5650M notes they can appear alongside B3935, suggesting widespread RFI is affecting multiple vehicle systems that rely on radio frequencies.

Technical Service Bulletins (TSBs) & Recalls

• PIC5650M: Addresses intermittent no crank/no start/start stall with security light on, listing B3935 as a possible code. Provides an extensive list of RFI sources including aftermarket LEDs, phone chargers, and toll passes.
• PIC5650L: Advises technicians not to replace parts for this concern and to first ask the customer about Radio Frequency Identification devices on their keychain.
• PIC5650K: A later revision that details the frequencies used by GM systems (125 kHz for passive entry) and suggests tools for detecting RFI.

Platform-Specific Known Issues

• GM Technical Service Bulletin PIC5650M directly links B3935 to intermittent no-start or start/stall conditions with the security light on, often caused by aftermarket equipment such as LED lights, phone chargers, and even decorative trim rings around the ignition.
• GM Technical Service Bulletin PIC5650L explicitly warns technicians *not* to replace any parts for this concern initially, but to first investigate RF interference from devices on the customer's keychain.
• A real-world forum post on ChevroletForum.com highlighted a no-crank condition on a 2015 Express 4500 with the anti-theft light on. After trying spare keys and checking the battery, the owner discovered a blown 2A fuse (F22) was the culprit.

Mechanic-Grade Diagnostic Values

• Immobilizer Antenna (Exciter Coil) Resistance — expected: 7-15 Ohms. Failure: A reading of 0 Ohms indicates a short, while an infinite (OL) reading indicates an open circuit in the coil.

Hidden / Shadow Codes Worth Checking

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

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > Body Control Module > Immobilizer Learn — This function is required to program new keys or to relearn existing keys after a BCM replacement or a system reset. It can resolve synchronization issues.
• GDS2 (GM Global Diagnostic System 2): Module Diagnostics > BCM > Data Display > Immobilizer Data — Use this to monitor the live status of the immobilizer system. Look for parameters like 'Transponder Key State' to see if it changes from 'Authenticated' to 'Invalid' when the fault occurs, which helps confirm an intermittent problem.

Wiring & Ground Locations

• Body Control Module (BCM) — Located behind the driver's side of the instrument panel, typically to the left of the steering column.. The BCM is the central module for the Passkey III+ system. All immobilizer signals are processed here. Loose connectors or internal faults in the BCM can cause B3935.
• G218 — A primary body ground point located behind the driver-side kick panel, near the A-pillar.. A poor connection at G218 is a known cause for various electrical issues on GM trucks and vans, including BCM malfunctions that can trigger security codes. TSB PIT5405C specifically calls out checking this ground for looseness or trapped insulation.
• Immobilizer Antenna (Exciter Coil) Connector — The wiring runs from the BCM to the ignition lock cylinder housing in the steering column.. The two wires (often purple and purple/white) carry the signal between the BCM and the antenna that energizes the key. Damage or chafing to these wires, especially where they flex with a tilt steering column, can cause an intermittent connection and trigger B3935.

Real Owner Repair Stories

• ChevroletForum.com user (Express 3500 4.8L (year not specified, but platform consistent)) — No crank, no start, and power locks not working immediately after a battery replacement.
  ❌ Tried (didn't work) Replacing the Body Control Module (BCM) with a cloned unit.
  ✅ What actually fixed it The owner performed a hard reset by disconnecting the battery and touching the positive and negative battery cables together for a moment. This fully drained residual power from all modules. After reconnecting, the van started and functioned normally.

OEM Part Supersession History

• 23300334 → 84538391 — Standard part number update/revision.

Model Year Variations Within This Range

• 2022-2026: There are no significant known variations within the 2022-2026 model years for the Chevrolet Express regarding the Passkey III+ immobilizer system. The diagnosis and common causes remain consistent across this range.