C056D on GMC: How to Diagnose & Fix
Electronic Brake Control Module Internal Fault (manufacturer-specific)
1 GMC model · 1 documented issue · 1 critical
C056D on GMC by model: symptoms, diagnosis and fix
On 2020+ Sierra 3500HD (T1 platform) with electric power steering, owners report intermittent loss of steering assist and warning messages such as "Steering Assist Reduced". NHTSA complaints and GM service information commonly point to EPS module/software issues, wiring/connector concerns, or rack-related faults that can occur without prior symptoms.
Common Symptoms
- "Steering Assist Reduced" or "Service Power Steering" message
- Heavier steering effort, especially at low speeds
- Intermittent assist loss after startup or during turns
- EPS warning light and stored steering control DTCs
- Assist returns after key cycle
How to Fix
Scan for EPS-related DTCs and follow GM SI diagnostics for the steering gear/module and harness. Perform GM-released software updates/reprogramming when applicable; repair wiring/connectors or replace the steering gear/rack assembly if internal faults are confirmed. Verify battery/charging system health because low voltage can trigger EPS faults.
Sources for this issue (1)
C056D code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does C056D mean on a GMC?
C056D stands for "Electronic Brake Control Module Internal Fault (manufacturer-specific)." C056D is a manufacturer-specific chassis code (frequently seen on GM vehicles) that generally indicates an internal hardware/electronics failure within the electronic brake control module (EBCM)/ABS assembly. When the module's own self-test detects a fault it cannot recover from, it disables ABS, traction control, and stability control and commonly triggers the 'Service StabiliTrak'/'Service Traction Control' messages. Because the fault is internal to the module, the usual repair is reprogramming or replacing the ABS/EBCM unit after confirming wiring and power/ground are good. Conventional braking still functions while the electronic aids are offline. On GMC it is documented across 1 model: Sierra 3500HD.
What are the most common causes of C056D?
The most common causes of C056D are: Internal EBCM/ABS module hardware failure, Corroded or damaged module connector/pins, Poor power or ground to the ABS module, Low battery voltage or charging system issues, Water intrusion/corrosion in the module, Module software/calibration corruption, Wiring faults at the brake module connector. The specific cause varies by vehicle.
How much does it cost to fix C056D on a GMC?
Repair costs vary widely with the root cause and GMC model; each issue on this page carries its own estimate where one is published.
Looking for C056D on a different make?
View C056D across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.