C0024 on 2020 Cadillac XT6: Loss of Brake Assist Causes and Fixes

What's Unique About the 2020-2020 Cadillac XT6

The 2020 Cadillac XT6 uses a sophisticated brake-by-wire system called 'eBoost' instead of a traditional vacuum-powered booster. This system integrates the master cylinder, electronic booster, and ABS control module into one assembly that relies on sensors and an electric motor to generate hydraulic pressure. For this specific model year and its platform mates, a known software issue can cause the Brake System Control Module (BSCM) to incorrectly calculate solenoid temperatures or determine that motor position sensors do not correlate, falsely triggering code C0024 even when no mechanical parts have failed. This issue is widespread enough that GM issued Technical Service Bulletin #20-NA-073 to address it with a specific software update.

Diagnostic Flowchart

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

Symptoms You May Notice

• Loss of power brake assist
• Brake pedal feels harder to press or requires significantly more effort
🎬 See this guide on common symptoms of a failing brake booster.
• Brake pedal travel may feel longer or softer than normal
• "Service Brake Assist" or other warning messages displayed in the Driver Information Center (DIC)
🎬 Watch: What the Service Brake Assist message means for your Cadillac.
• ABS or Traction Control warning lights may illuminate

Most Likely Causes

1. Brake System Control Module (BSCM) Software Error 🔴 High Probability A specific software issue was identified by GM where the module's 'model-based calculated solenoid temperature' deviates from the actual temperature, or where motor position sensors do not correlate, falsely triggering the DTC.
   How to confirm: A GM dealer or qualified shop with access to GM's Service Programming System (SPS) can check the current software calibration of the BSCM against the latest version specified in TSB #20-NA-073.
   Typical fix: Reprogram the Brake System Control Module (BSCM) with the updated software calibration provided by GM, following the exact procedure in the TSB. This repair may be covered under the Federal Emissions Warranty (8 years / 80,000 miles).
   Est. part cost: $0

Rare But Worth Checking

• Failed Brake System Control Module (BSCM) / eBoost Assembly: If reprogramming the module does not resolve the code, the module itself (which is integrated into the eBoost assembly) may have an internal hardware failure. This is much less common than the software issue.
• Wiring Harness or Connector Issue: Damage to the wiring or a corroded connector at the eBoost assembly or BSCM could cause a loss of communication or power, triggering the code. This is unlikely unless the vehicle has been in an accident or has flood damage.
• Low System Voltage: Modern electronic modules, especially safety-critical ones like the BSCM, are highly sensitive to battery voltage. A failing battery or alternator can cause unpredictable behavior and trigger various fault codes, including C0024. A Reddit user with similar driver assist issues on an XT6 noted their problem was suspected to be an incorrect (EFB instead of AGM) battery type.

Diagnosis Steps

1. Verify the presence of DTC C0024 using a professional OBD-II scanner capable of reading Chassis codes.
2. Check for a symptom byte using a GM-level scan tool. C0024 5A ('Not Plausible') strongly indicates the software issue described in the TSB.
3. Check for any other related DTCs, particularly those mentioned in TSB #20-NA-073 (P0606, C0021, C05D2, C0595, C2A3B, C053D, P25A2).
4. Connect the vehicle to GM's Service Programming System (SPS) to check the current software version of the Brake System Control Module (BSCM).
5. CRITICAL: Before programming, ensure the computer is connected via a network cable (hardwired), NOT wirelessly.
6. CRITICAL: Connect a GM Authorized Programming Support Tool or a fully charged booster pack to maintain stable system voltage. Do NOT use a standard battery charger.
7. If the software is outdated, perform the BSCM reprogramming procedure as detailed in TSB #20-NA-073.
8. After reprogramming, clear all DTCs and perform a test drive to ensure the code does not return.
9. If the code returns after the software update, perform a detailed inspection of the wiring and connectors for the eBoost system, paying close attention to the main ground connection for the module.
10. If wiring is intact and the code persists, the Brake System Control Module (as part of the entire eBoost assembly) may require replacement.

Parts You'll Likely Need

• Brake System Control Module (BSCM) Reprogramming — This is not a physical part, but a software update that corrects the logic error causing the false DTC. It is the official fix from GM and the most common solution. This service may be covered under the 8yr/80k mile emissions warranty.
  Trusted brands: GM (Dealer Service)
  OEM price range: $150-$350 (Labor for programming, typically 1-1.5 hours at dealer rates).
  Aftermarket price range: N/A
• eBoost Brake Booster / Control Module Assembly (OEM #84401914 (replaces 84329995)) — This entire hardware assembly is only replaced in the rare event that the BSCM has a hardware failure and does not respond to or fails after the software update. This part number is for related platforms and should be verified with a dealer using the vehicle's VIN.
  Trusted brands: ACDelco, GM Genuine
  OEM price range: $600-$900
  Aftermarket price range: $400-$700 (Remanufactured)

Related Codes That Often Appear With This One

• P0606 — Indicates a general internal performance problem with a control module, often set in conjunction with more specific fault codes like C0024.
• C0021 — Relates to Brake Booster Performance, indicating the system has detected an issue with the brake assist function.
• C05D2 — Points to a fault with the Brake Master Cylinder Piston Excessive Travel, which is directly related to the software issue described in the TSB.
• P25A2 — Another code related to Brake Booster Performance, often triggered by the same underlying fault as C0024.
• C0595 — An additional code related to Brake System Control Module Internal Driver Performance that GM added to the list of potential related DTCs in a TSB revision.
• C2A3B — An additional code related to a 'Hydraulic Shutdown Test Not Run' that GM added to the list of potential related DTCs in a TSB revision.
• C053D — An additional code related to Brake Pressure Sensor Circuit Performance that GM added to the list of potential related DTCs in a TSB revision.

Technical Service Bulletins (TSBs) & Recalls

• 20-NA-073 (revised June 2, 2020): Loss of Brake Assist, Various Messages Displayed in Driver Information Center (DIC), Brake Pedal Travel and Apply May Feel Different, One or More of the Following DTCs May be Set: P0606 with C0021, C05D2, C0595, C2A3B, C0024, C053D, and P25A2.

Platform-Specific Known Issues

• The 2020 Cadillac XT6 is subject to Technical Service Bulletin #20-NA-073, which directly addresses DTC C0024. The bulletin confirms the cause is a software error within the Brake System Control Module (BSCM) and the official correction is to reprogram the module. This TSB also applies to the 2020 XT5, 2020 Blazer, 2020 Acadia, and 2019-2020 Silverado/Sierra trucks.

Hidden / Shadow Codes Worth Checking

• C0024 5A: The symptom byte '5A' indicates a 'Not Plausible' signal. This directly aligns with the TSB's description of the fault, where the module's calculated software values (like solenoid temperature) do not match the expected physical reality, confirming the software glitch as the root cause. (see via GM GDS2 (Global Diagnostic System 2) or an equivalent high-end professional scan tool capable of reading manufacturer-specific symptom bytes.)

Scan Tool Commands That Help

• GDS2 (GM Global Diagnostic System 2): Module Programming > K17 Brake System Control Module (BSCM) — This is the primary function used to perform the software update as specified in TSB #20-NA-073. It is the first and most critical diagnostic step.
• GDS2 (or equivalent professional scan tool): Automated Bleed Procedure — This function is required if the eBoost hydraulic assembly (Brake Pressure Modulator Valve) is replaced. The procedure cycles the internal ABS solenoids and pump to purge trapped air from the new component, which cannot be done with a manual bleed alone.

Wiring & Ground Locations

• F36 Underhood Fuse Block — Located in the main fuse block in the engine compartment.. This 40A J-Case fuse supplies power to the 'Electronic brake control module electric brake booster'. A loss of power from this fuse would cause a total failure of the eBoost system and set multiple DTCs, including C0024.

OEM Part Supersession History

• 84329995 → 84401914 — Standard part evolution for design improvements, software compatibility, or manufacturing changes.
  Heads up: The new part (84401914) requires programming and setup procedures after installation using GM's Service Information to function correctly in the vehicle.