B3924 on 2019-2023 Cadillac XT4: 'No FOB Detected' and No-Start Causes

What's Unique About the 2019-2023 Cadillac XT4

The Cadillac XT4, along with many other GM vehicles from this era using the 'GEN3R' BCM, is highly susceptible to memory corruption after a voltage fluctuation (like a battery change or jump-start). This known issue is documented in Technical Service Bulletin #23-NA-163. As a result, code B3924 is far more likely to be a software glitch requiring a dealer reset than an actual failed antenna. This is a common misdiagnosis that leads to unnecessary and expensive parts replacement. The TSB explicitly warns technicians not to replace modules before performing the software procedure.

Diagnostic Flowchart

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

Symptoms You May Notice

• "No FOB Detected" message on the instrument cluster.
• Engine will not crank or start (No Crank/No Start).
• Engine starts and immediately stalls.
• Key fobs are completely inoperative for passive functions (passive entry, push-start).
• Push-button start does not work.
• Message on DIC to "Place Key in Transmitter Pocket 🎬 Watch: How to start your XT4 with a dead key fob".

Most Likely Causes

1. Body Control Module (BCM) Memory Corruption 🔴 High Probability → Shop Body Control Module A known issue documented in TSB #23-NA-163 shows the specific 'GEN3R' BCM is sensitive to low-voltage events like a battery change, jump-start, or a failing battery, which can scramble its security memory. This is a software glitch, not a hardware failure.
   How to confirm: The problem appeared immediately after a low-voltage event. A professional scan tool (GM GDS2) shows DTC B389A 00 is current, along with B3924 00 and at least two other antenna codes (B3925, B3926, B3927). The technician must also verify the BCM is a 'GEN3R' type via its part number.
   Typical fix: Perform a BCM data reset/reprogramming procedure using the GM Service Programming System (SPS) as detailed in TSB #23-NA-163. This is a software-only fix that involves either 'Programming A' or 'Programming B' followed by an immobilizer relearn.
   Est. part cost: $0
2. Faulty Keyless Entry Antenna or Wiring ⚪ Low Probability → Shop Antenna While less common than the software issue, the antenna itself (B3924 often corresponds to Antenna 4 in the center console or rear of the vehicle) or its wiring can fail like any other electronic component. Rear antennas can be vulnerable to minor impacts or water intrusion.
   How to confirm: The code B3924 appears by itself, without the other antenna codes or B389A, and there was no recent low-voltage event. A technician would test the specific antenna circuit for continuity, shorts, or damage.
   Typical fix: Replace the faulty keyless entry antenna and/or repair the damaged wiring.
   Est. part cost: $15-$90

Rare But Worth Checking

• Parasitic Drain Causing Low Voltage:

Diagnosis Steps

1. Note if the symptoms began immediately following a battery replacement, jump-start, or other low-voltage event. This is the primary trigger.
2. Try the backup starting procedure: Place the key fob flat in the front cupholder and then press the start button with your foot on the brake. This may allow you to start the vehicle to get it to a shop.
3. Have the vehicle scanned with a professional tool capable of reading GM-specific Body Control Module codes and symptom bytes (e.g., GM GDS2).
4. Confirm the presence of DTC B389A 00. If it is not present, disconnect and reconnect the battery for at least 30 seconds and re-check.
5. Check for B3924 00 and at least two other codes from the B3925-B3928 range.
6. If B389A and multiple antenna codes are present, the cause is almost certainly the BCM software glitch per TSB #23-NA-163. The vehicle requires dealer service for reprogramming.
7. If B3924 appears alone and with no history of a voltage event, proceed with electrical testing of the specified keyless entry antenna circuit, checking for opens, shorts, or damage to the wiring and connector.

Parts You'll Likely Need

• No parts needed - BCM Reprogramming — The most common cause is a software glitch that is resolved by reprogramming the existing BCM, not by replacing hardware.
  OEM price range: $0
  Aftermarket price range: $0
• Keyless Entry Antenna (OEM #13545326) — In the rare case of an actual hardware failure, the specific antenna that has failed will need to be replaced. B3924 often corresponds to the antenna in the center console or rear of the vehicle.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $15-$40
  Aftermarket price range: $10-$30

Related Codes That Often Appear With This One

• B3925, B3926, B3927, B3928 — These are codes for the other keyless entry antennas. When they appear together with B3924 (specifically with a '00' symptom byte), it strongly indicates a system-wide BCM software glitch rather than multiple simultaneous hardware failures.
• B389A — This is a primary 'Environment Identification' code. Its presence is the key indicator that the BCM has experienced the memory corruption event that triggers the secondary B3924 code. TSB #23-NA-163 states that B389A will be current along with three or more of the other antenna codes.

Technical Service Bulletins (TSBs) & Recalls

• 23-NA-163: Addresses a 'No Crank, No Start, Quick Start/Stall, No FOB Detected, Key FOBs Inoperative' condition where codes like B3924 00 are set due to BCM memory corruption. It provides a specific software-based repair procedure for 'GEN3R' BCMs and explicitly warns against replacing parts first.

Platform-Specific Known Issues

• The 2019-2023 Cadillac XT4 is explicitly covered by GM Technical Service Bulletin #23-NA-163 for a condition where a low-voltage event can corrupt the 'GEN3R' BCM's memory, causing a no-start condition and setting code B3924 among others.
• Some 2023 XT4 models were also subject to TSB #22-NA-221 for a parasitic battery drain caused by the BCM, which can create the low-voltage condition that triggers the B3924 fault.
• Owners report other electrical gremlins after a battery change, such as power windows needing recalibration, further highlighting the platform's sensitivity to voltage events.

Hidden / Shadow Codes Worth Checking

• B3924 00: Indicates 'No Additional Symptom Information' or a general electrical failure. When seen with B389A and other antenna codes, it confirms the BCM memory corruption issue per TSB 23-NA-163. (see via GM GDS2 or equivalent professional scan tool.)
• B3924 02: Indicates 'Circuit Short to Ground'. This points specifically to a wiring or antenna hardware fault, not the TSB software glitch. (see via GM GDS2 or equivalent professional scan tool.)
• B3924 04: Indicates 'Circuit Open'. This points specifically to a broken wire or failed antenna, not the TSB software glitch. (see via GM GDS2 or equivalent professional scan tool.)
• B3924 5A: Indicates 'Signal Plausibility Failure'. This suggests the signal from the antenna is present but incorrect or irrational, pointing to a hardware or interference issue. (see via GM GDS2 or equivalent professional scan tool.)

Scan Tool Commands That Help

• GM SPS (Service Programming System): K9 Body Control Module > Programming A Per Bulletin 23-NA-163 and 23-NA-165 Only — This is the primary software fix for the BCM memory corruption. It must be performed first, followed by an immobilizer relearn.
• GM SPS (Service Programming System): Immobilizer procedure > Body Control Module IMMO Learn with Existing Transponder or Remote Key — This procedure must be performed immediately after executing 'Programming A' to re-synchronize the existing key fobs with the reprogrammed BCM.
• GM SPS (Service Programming System): K9 Body Control Module > Programming B Per Bulletin 23-NA-163 Only — This is a secondary recovery procedure used ONLY if 'Programming A' and the subsequent key learn do not resolve the no-start condition, or if an immobilizer learn was incorrectly attempted before starting the TSB procedure.
• GM GDS2: Module Diagnostics > [K9] Body Control Module > Identification Information — Used to view the BCM's Base Model Part Number (BMPN) to confirm it is a 'GEN3R' type, which is the only BCM hardware eligible for the TSB 23-NA-163 software fix.

Wiring & Ground Locations

• Body Control Module (BCM) — For the 2023 XT4, the BCM is located on the passenger's side. Access requires moving the passenger seat fully rearward and removing the right side front floor console extension panel.. This is the module that sets the code and requires reprogramming. A service update (N222390510) was issued for some 2023 models for improperly seated BCM connectors, which could cause various electrical faults.
• Keyless Entry Antenna 4 — While specific diagrams for the XT4 are scarce, on similar GM platforms this antenna is typically located in the rear console or rear bumper area.. In the rare case of a true hardware failure (not the software glitch), this antenna or its wiring is the component that has failed. Its location is necessary for inspection and replacement.
• BCM Ground Pin — On the K9 BCM X2 connector, Pin 2 (typically a Black/White wire) serves as the main ground for the module.. While the primary cause is a software glitch from a voltage event, a poor ground connection at the BCM itself could cause erratic behavior, communication faults, and potentially trigger the memory corruption. This is a secondary check if reprogramming fails.

Real Owner Repair Stories

• Reddit user /u/Sudden-Taro-910 (Cadillac XTS (similar GM platform)) — After disconnecting the battery for a few days, the car would not start unless the key fob was placed in the backup slot. The fob could still remote start, lock/unlock, and pop the trunk, but passive entry and keyless start did not work. Displayed 'No key detected'.
  ❌ Tried (didn't work) Replacing the RCDLR (Remote Control Door Lock Receiver) module., Attempting the standard key fob reprogramming procedure.
  ✅ What actually fixed it The user noted that others with the same issue found pinched or damaged wiring for the RCDLR module, often near the rear seat or pillars, and repairing the wire resolved the problem. This points to a potential wiring issue as an alternative cause if the TSB software fix does not apply.

OEM Part Supersession History

• 13592452 → 13545326 — Part has been updated by the manufacturer.
  Heads up: The new part number (13545326) is the correct replacement for the older number (13592452) for the Keyless Entry Antenna.

Model Year Variations Within This Range

• 2023: Certain 2023 Cadillac XT4 vehicles are subject to Service Update N222390510 for improperly seated BCM connectors from the factory. This could cause a variety of electrical issues, including those related to the keyless entry system, and should be checked before performing software repairs.