B1038 on 2021-2022 Cadillac CT5: Understanding the Door Ajar Message and Fixes

What's Unique About the 2021-2022 Cadillac CT5

Unlike many vehicles where a door ajar message points directly to a faulty door latch, General Motors has identified a platform-specific issue for the CT5 and several other models. A Technical Service Bulletin (TSB 22-NA-052) states that the root cause is often an internal fault or software glitch within the Body Control Module (BCM). The bulletin explicitly advises technicians *not* to replace the door latch assembly as the first step, which is a common misdiagnosis.

Diagnostic Flowchart

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

Symptoms You May Notice

• A 'Door Ajar' message appearing on the Driver Information Center (DIC) when all doors are closed.
• Interior dome/courtesy lights staying on, which can lead to a drained battery.
• In some cases, customers may comment on door latches being inoperable.
• A Reddit user with a CT5 mentioned an issue where the driver's side exterior door actuator would not work reliably, requiring a specific 'adventure' to get the door open, which was scheduled for a fix.
🎬 See a quick fix for an unresponsive exterior door handle

Most Likely Causes

1. Body Control Module (BCM) Software/Internal Fault 🔴 High Probability → Shop Body Control Module A specific GM Technical Service Bulletin (22-NA-052) identifies this as the primary cause for this model year range and a wide range of other GM vehicles.
   How to confirm: Perform a BCM reset by removing fuses F49DR (BCM1) and F4DR (BCM2) for five minutes. If the code clears and stays away, it was a temporary glitch. If it returns, contact a dealer to check for a BCM software update.
   Typical fix: A temporary fix is a BCM power cycle (fuse pull). The long-term fix is a BCM software update performed by a GM dealership. In rare cases where the module has an internal hardware failure, the BCM itself may need replacement, which can cost between $450 and $1,000 at a dealer.
   Est. part cost: $0 for a reset, dealer cost for software update varies (approx. $145-$250), or $300-$600 for a new BCM part.
2. Faulty Door Latch Assembly ⚪ Low Probability → Shop Door Latch Assembly While modern door latches contain integrated sensors that can fail, the TSB for this vehicle points to the BCM as the more likely culprit. This should be considered a secondary possibility.
   How to confirm: This should only be suspected if the BCM reset and software update do not resolve the code. A technician would then test the wiring and signal from the specific door latch indicated by the scan tool.
   Typical fix: Replacement of the affected door latch assembly.
   Est. part cost: $60-$170

Rare But Worth Checking

• Wiring or Connector Issue: A damaged wire or loose/corroded connector between the BCM and the door latch assembly could also cause a signal fault. This would typically be investigated after the BCM software has been ruled out as the cause.

Diagnosis Steps

1. Confirm the presence of DTC B1038 with symptom code 64 using a compatible OBD-II scanner.
2. As a first step, attempt to reset the Body Control Module. Turn the vehicle off.
3. Locate the BCM fuses in the instrument panel fuse block. 🎬 Watch: How to find the fuse box on your CT5 According to TSB 22-NA-052, these are F49DR (BCM1) and F4DR (BCM2).
4. Remove both fuses simultaneously and wait for at least 5 minutes.
5. Reinstall the fuses securely.
6. Start the vehicle, clear all DTCs with the scan tool, and check if code B1038 returns.
7. If the code does not return, the issue may be resolved. If it returns, professional service is required.
8. Contact a GM dealership and reference TSB #22-NA-052. Inquire if the BCM software update is available and applicable to your vehicle's VIN.
9. The dealer service for the BCM reset is filed under labor operation code 2888588 and takes approximately 0.3 hours.
10. If the software is up-to-date and the code persists, the dealer will then follow standard diagnostic procedures to test the wiring and the door latch assembly itself.

Parts You'll Likely Need

• Door Latch Assembly (OEM #13540963) — This part is only needed if the BCM reset and software update fail to fix the problem. It contains the sensor that reports the door's status to the BCM.
  Trusted brands: GM Genuine Parts, ACDelco
  OEM price range: $115-$170
  Aftermarket price range: $60-$120
• Body Control Module (BCM) — The TSB identifies an internal fault in the BCM as a primary cause. Replacement is a last resort after software updates and requires programming by the dealer. A new BCM from a dealer can cost $300-$600 for the part alone.
  Trusted brands: GM Genuine Parts
  OEM price range: $300-$600 (part only, requires dealer programming)
  Aftermarket price range: Not recommended, as used BCMs often cannot be reprogrammed to a new vehicle.

Related Codes That Often Appear With This One

• B2A00: An updated version of TSB 22-NA-052 added this DTC as a related keyword, suggesting it may appear alongside B1038 in some cases.

Technical Service Bulletins (TSBs) & Recalls

• 22-NA-052: Diagnostic Trouble Code (DTC) B1038 SYM64 Set in Body Control Module (BCM) and Door Ajar Message on Driver Information Center (DIC).

Platform-Specific Known Issues

• GM issued Technical Service Bulletin #22-NA-052 specifically to address DTC B1038 SYM64 on this and other vehicles, pointing to a BCM fault rather than a latch failure.

Hidden / Shadow Codes Worth Checking

• B1038 SYM64 (or B1038.64): This is the specific fault code combination addressed by TSB 22-NA-052. The 'SYM64' is a GM-specific symptom byte that typically translates to 'Signal Plausibility Failure,' meaning the BCM received a signal from the door latch that is not logical or expected (e.g., showing both open and closed at the same time). (see via A professional scan tool capable of reading GM-specific body codes, such as the dealer's GDS2 software.)

Scan Tool Commands That Help

• GDS2 (GM Diagnostic Software): BCM > Data Display > Vehicle Access Data — While not for B1038 directly, a related GM document for a 'Service Door Latch System' message advises technicians to use this path to monitor parameters like 'Right Rear Child Security Lock - Lock Command' and 'Left Rear Child Security Lock - Lock Command' to check for synchronization issues between components, which can point to BCM or latch communication problems.
• GDS2 (GM Diagnostic Software): Clear All DTCs — This is a required step after performing the BCM fuse-pull reset. The TSB specifies that after reinstalling the fuses, the technician must use the scan tool to clear codes and verify that B1038.64 does not immediately return.

Wiring & Ground Locations

• G300 / G303 (Example) — On similar GM vehicle platforms, grounds for door components are often located on the B-pillar behind the trim panel (G303) or on the floor near the B-pillar under the seat/carpet (G300).. A loose or corroded ground connection for the door latch assembly could cause erratic signals, mimicking the symptoms of B1038. If the BCM software update does not fix the issue, checking the integrity of the relevant ground point is a key step in diagnosing a potential wiring fault.
• Door Jamb Harness — The flexible rubber conduit between the vehicle body and the door.. This harness contains the wires running from the BCM to the door latch and handle. Repeated opening and closing of the door can cause wires to fatigue and break over time, leading to a loss of signal. This is a common failure point for any door-mounted electrical component.

Real Owner Repair Stories

• Reddit user PC--loadletter in r/CadillacV_Series (2021 Cadillac CT5-V) — The driver's side exterior door would not pop open when using the handle's button. The owner had to open another door and reach in, or use the key fob to lower the windows to get in.
  ❌ Tried (didn't work) The user went straight to diagnosing the handle assembly.
  ✅ What actually fixed it The owner purchased a new exterior door handle assembly for approximately $250 but only used the microswitch from within the new part to repair the original handle. This avoided the need to paint a new handle. The fix involved removing the interior door panel and the exterior handle to swap the switch, which resolved the problem.