C056D: A control module reports an internal hardware fault

Electronic control unit hardware / internal malfunction

Severity: Inspect soon

The module has found an internal fault and Saab service information says it then refuses further inputs; owners of GM cars report losing power steering assist suddenly with this code.

It gets more serious if:

Stop: Stop driving and have it towed if a Service Power Steering message shows and the steering turns heavy, since you lose assist.

Safety-critical system: explanation only, no DIY steps. Source: how we rate severity

C056D in short

C056D means a control module found an internal hardware fault. On GM cars it most often points to the power steering module, with a Service Power Steering message and sudden heavy steering. On others it can be the brake or rear differential module. Check the code is current, and have a shop confirm.

C056D is a module reporting on itself: it ran its own check at power-up and found an internal fault. Saab service information says the module then refuses additional inputs, and that a code stored only as history, not current, does not call for replacing the module.

Which module it is depends on the car. Owner complaints on Chevrolet and Buick quote GM dealers and scan tools naming the power steering module (Impala, Encore, Colorado, Volt, Malibu). A Cadillac SRX owner quotes a mechanic reading it as a brake module hardware fault, and a GMC Terrain dealer found it in the rear differential module and reprogrammed it.

The Volt complaint has the dealer finding the code with GM bulletin 18-NA-313; the bulletin itself was not read.

Most likely causes

Cause 1: Power steering control module internal fault
Supported by vehicle data
Why it ranks here
Most owner complaints with dealer or scan-tool readouts, on Impala, Encore and Volt, name the power steering module, often replaced as part of the column or gear.
What would change this
Rises if the Service Power Steering message shows with the code. Falls if the code is stored in another module.
How to test the power steering control module
Cause 2: Another module reporting its own hardware fault
Supported by vehicle data
Why it ranks here
A brake module reading on the SRX and a rear differential module reprogram on the Terrain show the code is not limited to steering.
What would change this
Rises if the code sits in the brake or driveline module list. Falls if it sits in the steering module.
Cause 3: Low voltage or a bad power or ground to the module
Possible — needs testing
Why it ranks here
Saab notes the module needs only voltage and ground to run its self-check, so power problems are worth ruling out before replacement.
What would change this
Rises if battery voltage is low or connections look corroded. Falls if supply and ground test normal.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: With a scan tool, note which module stored C056D and whether it is current or history only.
Low riskTool: scan tool that reads all modules
- IfHistory only and no steering or brake symptoms
  It meansSaab says the module should not be replaced on a history-only code.
  Go to step 2
- IfCurrent in the power steering module
  It meansInternal module fault is likely.
  Points to: Power steering control module internal fault
- IfCurrent in a brake or driveline module
  It meansThat module is reporting its own fault.
  Points to: Another module reporting its own hardware fault
Step 2: Have the battery, connectors and grounds for that module checked.
Best left to a shopTool: multimeter
Warning:Steering and brake modules are safety systems. Leave the testing to a shop.
- IfVoltage or ground is poor
  It meansRepair the supply first.
  Points to: Low voltage or a bad power or ground to the module
- IfSupply is normal and the code is current
  It meansModule internal fault; a shop will confirm and program the replacement.
  Points to: Power steering control module internal fault

Symptoms

Service Power Steering message on the dash
Steering suddenly heavy with no assist Gets more serious: stop and have it checked.
StabiliTrak or stability control light on
Service all-wheel drive message on some models

How to fix

This is a safety-critical system, so we explain the code but don't give repair steps. Have it inspected by a qualified technician.

Parts and cost context

Power steering control module:On several GM models the module is part of the column or gear, so the repair can be large. Labor varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Chevrolet

2018 · Volt
Supported by vehicle data
An owner reports a dealer finding C056D with GM bulletin 18-NA-313 after a Volt lost power steering assist. The bulletin was not read, so this is owner-reported.

Buick

2016 · Encore
Supported by vehicle data
An owner quotes a dealer invoice naming internal failure of the power steering module for C056D; the column with module was replaced and programmed.

No curated relationships for C056D yet.

All Power steering and steering sensors codes

C056D questions

Is it safe to drive with C056D and a Service Power Steering message?

Not if the steering turns heavy. Owners report sudden loss of assist, so have it towed rather than driven.

Should the module be replaced straight away?

Only if the code is current. Saab says a history-only code does not call for replacement.

Sources and review

DTC C056D (9-5 9650 2011) — Saab Workshop Information System (SaabWISonline mirror)
NHTSA complaint ODI 11042674: 2016 Buick Encore power steering failure — NHTSA Office of Defects Investigation
NHTSA complaint ODI 10991338: 2017 Chevrolet Impala lost steering assist — NHTSA Office of Defects Investigation
NHTSA complaint ODI 11375073: 2018 Chevrolet Volt power steering lost — NHTSA Office of Defects Investigation
NHTSA complaint ODI 11690783: 2015 Cadillac SRX StabiliTrak light — NHTSA Office of Defects Investigation
NHTSA complaint ODI 11570919: 2022 GMC Terrain service all wheel drive — NHTSA Office of Defects Investigation

Last reviewed: October 15, 2026
Written by: Saurabh K.
Editorial review: Pending
Technician review: Technician review pending

This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error

Severity: Inspect soon

Most likely causes

Cause 1: Power steering control module internal fault

Cause 2: Another module reporting its own hardware fault

Cause 3: Low voltage or a bad power or ground to the module

What to test first

Step 1: With a scan tool, note which module stored C056D and whether it is current or history only.

Step 2: Have the battery, connectors and grounds for that module checked.