B3935 on 2015-2019 Cadillac ATS-V: No-Start Causes and Security Fixes

What's Unique About the 2015-2019 Cadillac ATS-V

On modern, high-feature GM vehicles like the Cadillac ATS-V built on the Alpha platform, the key fob and push-start systems are sensitive to a wide range of radio frequencies. The issue is rarely a faulty component on the vehicle itself, but rather external interference that disrupts the delicate 125 kHz communication between the key and the car's security module. GM has issued multiple evolving Technical Service Bulletins, including #PIC5650M, advising technicians to investigate RFI from keychains crowded with other fobs, access cards, toll passes, aftermarket phone chargers, and even non-OEM LED lights before replacing any parts.

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 (no-crank)
• Engine cranks but will not start (crank-no-start)
• Engine starts and immediately stalls
• Security/anti-theft light is illuminated or flashing on the instrument cluster.
• "No Key Detected" or "Service Theft Deterrent System" message on the driver information center.

Most Likely Causes

1. Radio Frequency Interference (RFI) 🔴 High Probability The vehicle's security system operates on a frequency (125 kHz) that is easily disrupted by other electronic devices. TSB PIC5650M specifically lists other vehicle key fobs, garage door openers, RFID access cards, toll passes, low-quality aftermarket phone chargers, and aftermarket LED lights as common culprits.
   How to confirm: Remove the Cadillac ATS-V key fob from your keychain. Ensure no other keys, fobs, or electronic devices are near the ignition or push-start button. Unplug all accessories (phone chargers, dash cams, etc.) from the vehicle's power outlets. If the car starts consistently with the key isolated, RFI is the cause. If it still fails, try placing the key fob in the designated transmitter pocket 🎬 Watch: How to start your Cadillac with a dead key fob (located inside the center console storage area) which is designed to overcome interference.
   Typical fix: Keep the vehicle key separate from other electronic devices. No parts replacement is needed.
   Est. part cost: $0
2. Weak or Defective Key Fob 🟡 Medium Probability → Shop Keyless Entry Transmitter The internal battery (CR2032) of the key fob can become weak, preventing it from properly completing the cryptographic handshake. The transponder chip itself can also fail over time from being dropped or from age, which was the confirmed fix for one owner of a platform-mate vehicle.
   How to confirm: First, try replacing the CR2032 battery 🎬 See this quick walkthrough for replacing your key fob battery in the key fob. If that does not work, try starting the vehicle with your spare key fob. If the spare key works reliably, the primary key is faulty.
   Typical fix: Replace the key fob battery. If the fob itself is faulty, a new one must be purchased and professionally programmed to the vehicle 🎬 Watch: How to program a new Cadillac ATS smart key by a dealership or qualified automotive locksmith.
   Est. part cost: $5-$300
3. Weak Vehicle Battery ⚪ Low Probability → Shop Vehicle Battery Low system voltage during cranking can cause various electronic modules, including the BCM, to behave erratically and fail to communicate properly, leading to a false authentication error.
   How to confirm: Test the 12V battery with a multimeter or a battery tester. A healthy battery should read approximately 12.6V at rest and should not drop below 10V during cranking.
   Typical fix: Recharge or replace the vehicle's 12V battery.
   Est. part cost: $150-$350

Rare But Worth Checking

• BCM Software Glitch: For 2015 models in particular, TSB PI1180A notes that a no-start condition with both B3935 and B2955 set may be resolved by reprogramming the BCM with updated software. This should be investigated before module replacement.
• Faulty Body Control Module (BCM): → Shop Body Control Module This is rare and should only be considered after all other causes, especially RFI and key fob issues, have been exhaustively ruled out. The BCM is an expensive component that requires programming. A GM bulletin warns that the BCM can be damaged if its ground path is removed while the battery is connected.
• Damaged Immobilizer Antenna/Wiring: → Shop Antenna The antenna (exciter coil) that reads the key transponder, or its wiring, can be damaged, though this is uncommon. This would typically set other codes like B3055 as well.

Diagnosis Steps

1. Verify that code B3935 is present using an OBD-II scanner capable of reading Body (B-prefix) codes.
2. CRITICAL FIRST STEP: Completely isolate the Cadillac ATS-V key fob from all other keys, fobs, and RFID cards. Remove all aftermarket accessories (phone chargers, dash cams, LED lights, etc.) from power outlets.
3. Attempt to start the vehicle with the isolated key. If it starts, the issue is RFI. The diagnosis is complete.
4. If the vehicle still does not start, place the key fob into the designated transmitter pocket (inside the center console storage area) and attempt to start. If it starts now, this strongly confirms an RFI or weak key fob battery issue.
5. If the vehicle still does not start, replace the CR2032 battery inside the key fob.
6. Attempt to start the vehicle again. If it starts, the diagnosis is complete.
7. If the vehicle still does not start, attempt to start it with a known-good spare key. If the spare key works, the primary key is faulty and needs to be replaced and programmed.
8. If the spare key also fails to start the vehicle, test the main 12V vehicle battery to ensure it has adequate voltage (above 12.4V at rest).
9. If all the above steps fail, the vehicle requires professional diagnosis to inspect the BCM (checking for software updates per TSB PI1180A, especially on 2015 models), immobilizer antenna, and associated wiring.

Parts You'll Likely Need

• Key Fob Battery (OEM #CR2032) — A weak battery is a common cause for the key fob failing the authentication handshake or being susceptible to interference.
  Trusted brands: Energizer, Duracell, Panasonic
  OEM price range: $5-$10
  Aftermarket price range: $2-$8
• Key Fob (OEM #13598530 (interchangeable with 13580811, 13510254, 13594024, 13598507)) — If the transponder chip in the key has failed, the entire fob must be replaced and programmed to the vehicle. FCC ID is HYQ2AB.
  Trusted brands: ACDelco (OEM)
  OEM price range: $150-$300
  Aftermarket price range: $50-$150

Related Codes That Often Appear With This One

• B3055 — This code means 'No Transponder Modulation,' indicating the BCM received no signal from the key at all. It is listed in TSB PIC5650M as being caused by the same RFI that triggers B3935, or a completely dead key.
• B3060 — This code means 'Unprogrammed Transponder.' It can be set alongside B3935 if interference corrupts the key's signal, making it appear like an unknown key to the BCM. It is also mentioned in TSB PIC5650M.
• B2955 — Indicates a security sensor data circuit malfunction. According to TSB PI1180A, when this code appears with B3935 on some 2015 models, it points to a BCM software issue that requires a dealer reprogram.
• C0750, C0755, C0760, C0765, C0775 — These are Tire Pressure Monitor (TPM) sensor codes. The provided TSB #PIC5650M links them to B3935, suggesting that strong RFI can disrupt multiple vehicle systems that rely on radio communication simultaneously.

Technical Service Bulletins (TSBs) & Recalls

• PIC5650M: Addresses intermittent no crank, no start, or start stall concerns with the security light on, specifically mentioning B3935 and the need to investigate external RFI sources (like chargers, toll passes, other fobs) before replacing parts.
• PI1180A: Relevant for 2015 models, this bulletin addresses a no-start condition where B3935 is set along with B2955, indicating a BCM software issue that requires reprogramming.

Platform-Specific Known Issues

• Per TSB #PIC5650M, this vehicle is susceptible to intermittent no-start or start/stall conditions with code B3935 due to Radio Frequency Interference from devices on the owner's keychain or aftermarket accessories plugged into the vehicle.
• A key diagnostic step for this vehicle is to place the key fob in the transmitter pocket inside the center console, which is designed to allow the car to start even with a weak fob battery or in the presence of RFI.

Hidden / Shadow Codes Worth Checking

• B3935 57: The '57' is a symptom byte specifying 'Transponder Authentication Error.' It confirms the key was detected but failed the subsequent cryptographic challenge-response calculation with the Theft Deterrent Module (TDM). (see via A professional scan tool like the GM GDS2/Tech2 or a high-end aftermarket scanner capable of reading GM-specific body codes and their symptom bytes.)

Scan Tool Commands That Help

• GDS2 (GM Diagnostic Software): Immobilizer Learn / Add or Replace Key Fobs — This function is required after replacing a key fob or the Body Control Module (BCM). It guides the technician through the process of programming new keys to the vehicle's immobilizer system. The path is typically: Module Diagnostics -> Remote Control Door Lock Receiver -> Configure/Reset Functions -> Add or Replace Key Fobs.
• GDS2 (GM Diagnostic Software): Data Bus Diagnostic Tool — If communication issues are suspected with the BCM or other modules, this tool can be used to check which modules on the CAN bus are communicating. This helps isolate a non-responsive module or a wiring fault before attempting to replace parts.

Wiring & Ground Locations

• K9 Body Control Module (BCM) — On the Cadillac ATS, the BCM is located inside the passenger cabin, typically behind the driver's side lower dashboard or kick panel area.. The BCM contains the Theft Deterrent Module (TDM) logic for the immobilizer system. All key authentication signals are processed here. A poor connection or a fault in this module is a root cause of B3935, though less common than external factors.
• G201 — Located at the left (driver's side) kick panel area.. This is a major interior ground point for various components in the instrument panel harness. A loose or corroded G201 can cause erratic behavior in multiple electronic modules, including the BCM, potentially leading to false security codes.
• G218 — Located on the driver's side, behind the instrument panel, near the base of the A-pillar. On related GM platforms, this ground is notorious for having sound-deadening material trapped under the terminal, causing a poor connection.. TSB PIT5405C for related GM platforms identifies a poor connection at G218 as a direct cause of no-start conditions, stalling, and numerous communication DTCs due to an unstable ground for the BCM. Checking this ground for tightness and ensuring no insulation is trapped underneath is a critical step in advanced diagnosis.
• Immobilizer Antenna (Exciter Coil) — This is a ring antenna integrated into the push-to-start button assembly.. This antenna energizes the transponder chip in the key fob via a low-frequency signal. If the antenna's wiring is damaged or the antenna itself fails, the BCM will not receive a signal from the key, typically setting B3055 but sometimes contributing to B3935 if the signal is intermittent or corrupted.

When the Usual Fixes Don't Work

• While RFI is the most common cause, a DIY key relearn procedure exists for situations where all keys are lost or not recognized, which can sometimes resolve the issue without a trip to the dealer. The procedure involves a 30-minute sequence of turning the physical key in the driver's door lock cylinder and pressing the start button in 10-minute intervals. This forces the BCM to erase all known keys and learn the new key placed in the transmitter pocket. This can overcome a logic lock-up in the BCM that simple battery pulls or RFI elimination might not fix.

OEM Part Supersession History

• 13580811, 13510254, 13594024, 13598507 → 13598530 — Standard part evolution, consolidating previous numbers into a single replacement part number for the 5-button smart key.
  Heads up: All listed part numbers with FCC ID HYQ2AB are generally interchangeable for the 2015-2019 ATS-V, but programming is always required.

Model Year Variations Within This Range

• 2015: A specific BCM software glitch addressed by TSB PI1180A can cause a no-start with codes B3935 and B2955. Later models received updated software from the factory. For 2015 vehicles, checking for this available BCM reprogram should be done before considering module replacement.