B3935 on 2007-2010 Saturn SKY: No-Start Causes and Fixes

What's Unique About the 2007-2010 Saturn SKY

The Saturn SKY, along with its GM Kappa platform siblings, is particularly sensitive to this issue, not because of inherently faulty parts, but due to its susceptibility to Radio Frequency Interference (RFI). Manufacturer Technical Service Bulletins (TSBs) specifically advise technicians *not* to replace parts initially, but to first investigate RFI from other devices on the owner's keychain. This highlights a design sensitivity in the immobilizer system rather than a common component failure.

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
• Security light is on or flashing on the instrument cluster.
🎬 Watch: Understanding what your immobilizer light is telling you.
• A single click may be heard from the relays when turning the key, but the starter motor does not engage.
• Engine may start and then immediately stall (start-stall)

Most Likely Causes

1. Radio Frequency Interference (RFI) 🔴 High Probability The vehicle's immobilizer system operates at a frequency (125 kHz) that can be easily disrupted by other electronic devices. TSBs #PIC5650M and #PIC5650L directly point to this as a primary cause to investigate before any parts are replaced.
   How to confirm: Remove all other keys, key fobs, garage door openers, and any other electronic devices from the keychain. Try starting the vehicle with only the single Saturn SKY key. If the vehicle starts, RFI was the cause.
   Typical fix: Keep other electronic devices separate from the ignition key when starting and operating the vehicle.
   Est. part cost: $0
2. Damaged or Faulty Ignition Key 🟡 Medium Probability The transponder chip embedded in the key head can be damaged from being dropped or from normal wear and tear, causing it to fail the authentication challenge.
   How to confirm: Try starting the vehicle with a known-good spare key. If the spare key works consistently, the original key is faulty.
   Typical fix: Replace the faulty key. A new key must be cut and programmed to the vehicle by a dealership or an automotive locksmith with the proper equipment.
   Est. part cost: $70-$200
3. Weak or Faulty Key Fob Battery/Solder Joints ⚪ Low Probability While the key's transponder is often passive, issues within the key fob itself, like a dead battery or broken internal solder joints for the battery clip, can sometimes cause intermittent signal problems.
   How to confirm: Replace the battery in the key fob. If that fails, inspect the internal circuit board of the fob for any visible damage or broken solder points, particularly where the battery holder connects.
   Typical fix: Replace the key fob battery or re-solder the broken connections. If the fob is damaged beyond repair, it will need to be replaced and programmed.
   Est. part cost: $5-$150

Rare But Worth Checking

• Faulty Theft Deterrent Module (TDM): The TDM is the computer that manages the key authentication process. While not common, it can fail. Diagnostic procedures often suggest replacing the TDM only after a new, properly programmed key also fails to resolve the issue.
• Faulty Ignition Lock Cylinder or Antenna: The antenna that energizes and reads the key's transponder chip is a ring located around the ignition lock cylinder. A break in this antenna's wiring or a failure of the cylinder itself can prevent the key from being read correctly.

Diagnosis Steps

1. Verify the complaint: Confirm the no-crank/no-start condition and the illuminated security light.
2. Scan for DTCs: Check for B3935 and any other related codes like B3055 or B3060.
3. Isolate the Key: Remove all other keys, fobs, and electronic devices from the keychain. Attempt to start the engine with only the Saturn key. This is the most critical and first step.
4. Test with a Spare Key: If available, try starting the vehicle with a second, known-good key. If it starts, the primary key is the issue.
5. Inspect the Key: Visually inspect the original key for any cracks or damage to the plastic head where the transponder chip resides.
6. Check Key Fob Battery: Replace the battery inside the key fob as a low-cost diagnostic step.
7. Professional Diagnosis: If the above steps do not resolve the issue, the vehicle needs to be diagnosed by a professional. They will use a scan tool to monitor data from the Theft Deterrent Module and test the circuitry of the ignition cylinder's antenna ring and the TDM itself.

Parts You'll Likely Need

• Ignition Key — If RFI is ruled out, the most likely hardware failure is the transponder chip within the key itself. A spare key working is definitive proof.
  Trusted brands: ACDelco, Strattec
  OEM price range: $70-$150
  Aftermarket price range: $40-$90

Related Codes That Often Appear With This One

• B3055 — Relates to a problem with the key transponder. Often set alongside B3935 when there is an issue reading or authenticating the key. [TSB #PIC5650M, TSB #PIC5650L, 32, 62]
• B3060 — Indicates an issue with the transponder antenna circuit. It can appear with B3935 if the car is having trouble communicating with the key. [TSB #PIC5650M, TSB #PIC5650L, 32, 62]

Technical Service Bulletins (TSBs) & Recalls

• PIC5650M: Notes B3935 with no-crank/no-start and security light symptoms, advises checking for RFI.
• PIC5650L: Explicitly states not to replace parts for B3935 and to ask the customer about Radio Frequency Identification devices on their keychain.

Platform-Specific Known Issues

• This platform is highly susceptible to Radio Frequency Interference, as documented in GM TSBs #PIC5650M and #PIC5650L, which should be the first suspected cause.
• The 2007-2010 Saturn SKY was subject to a major recall for the ignition switch, which could also cause a no-start condition. While it typically presents different symptoms (power loss while driving), it's a known electrical issue on this vehicle.

Mechanic-Grade Diagnostic Values

• Voltage Drop at Ground Connection — expected: Less than 0.4 Volts. Failure: A reading of 0.4 Volts or more indicates excessive resistance in the ground circuit.

Scan Tool Commands That Help

• GM Tech 2 / GDS2: VTD Learn (Vehicle Theft Deterrent Learn) — This function is used within the Service Programming System (SPS) menu after replacing the Theft Deterrent Module (TDM) or Engine Control Module (ECM) to program the new module to the vehicle and existing keys.
• No Tool Required: 30-Minute Manual Relearn Procedure — Used to program a new key when all keys are lost, or to sync an existing key after a component replacement (like the TDM or ECM) if a scan tool is not available. It involves three consecutive 10-minute cycles of turning the ignition ON without starting the engine, waiting for the security light to turn off after each cycle.
🎬 See this step-by-step walkthrough of the manual key programming procedure.

Wiring & Ground Locations

• Theft Deterrent Module (TDM) — Located on the top right side of the steering column, near the ignition lock cylinder.. This is the module that reads the key transponder and sends the authentication signal. Its location is critical for inspection of its connector and wiring.
• G300 — Under the center console.. This is a major interior ground point. A loose or corroded G300 can cause a variety of intermittent electrical issues, including problems with the Body Control Module (BCM) and Theft Deterrent Module (TDM) which rely on a stable ground reference.
• Body Control Module (BCM) — Located to the right of the HVAC module, typically accessed by removing the passenger side lower dash/glove box area.. The BCM communicates with the TDM and controls the security indicator light on the instrument cluster. Faults in the BCM or its wiring/ground can mimic TDM issues.

OEM Part Supersession History

• 15778671, 22719734 → 25807440 — Part revision and consolidation by the manufacturer.
  Heads up: The newest part number, 25807440, is the correct service replacement for the earlier numbers. Always verify fitment with VIN, but this part is listed for the Saturn SKY and Pontiac Solstice. This part requires programming upon installation.