C056D: Electronic Control Unit Hardware Internal Malfunction (GM)
Severity: high
What it means: On GM vehicles, the module that set the code (often the electric power steering module) has found an internal hardware or software fault. The -39 subtype is a common version on power steering modules.
Safe to drive? Use caution. Power steering assist can drop out, making the wheel very heavy. Get it checked promptly.
Common symptoms
- Service Power Steering message
- Heavy steering or loss of assist
- Message may clear after a restart and come back
Likely causes, ranked
- Power steering module softwareShop
- Internal power steering module failureShop
- Low battery voltage or poor connectionsDIY
Vehicle-specific notes
- 2014–2014 Chevrolet Silverado: 1500 built before the VIN breakpoints: GM bulletin PI1273 ties a Service Power Steering message with C056D-39 to steering module software. The fix is an operating-system update that must be done with a fully charged battery. GMC Sierra 1500 is covered too. Read the full answer · Source
What it means: On GM vehicles, the module that set the code (often the electric power steering module) has found an internal hardware or software fault. The -39 subtype is a common version on power steering modules.
Severity: High. Safe to drive? Use caution. Power steering assist can drop out, making the wheel very heavy. Get it checked promptly.
DIY or shop?
Dealer or well-equipped shop. Some trucks need a software update. Others need a steering module or gear.
Before you replace parts
- Read all stored codes with a scan tool that can talk to the ABS, steering or body modules, not just the engine computer.
- Check battery voltage, grounds and the module connectors first. Low voltage can set chassis codes.
- Check your VIN for recalls, service bulletins and extended coverage.
- Clear the code only after a repair, then confirm it stays off.
Safety / mechanic note
Verify with a mechanic. Loss of power steering assist can make the vehicle hard to steer, especially at low speed. A code points to a circuit or system, not always a specific part.