Audi A4 (2011 – 2018) Electric Power Steering Rack

The Audi A4 (B8, 2011–2018) is the volume model of this range, which makes it the B8 we see this steering fault on most often. Its power steering rack is electromechanical — the assist motor and control module are integrated into the rack, with no hydraulic pump — and the failure is in the electronics inside that unit rather than the mechanical rack. On some A4s the fault arrives with the car refusing to start at all. We repair the A4’s original rack and steering ECU at component level and return the same unit, reinforced against the fault returning.

The symptoms to watch for

The clearest sign is the red “Steering defective! Do not drive vehicle!” message on the cluster. It means precisely what it says — do not continue driving the A4 once it is active.

• Red “Steering defective! Do not drive vehicle!” warning on the cluster
• Heavy, unassisted steering, most obvious when parking and manoeuvring
• Loss of self-centre as you unwind the wheel out of a turn
• The warning appearing intermittently at first, then becoming permanent
• On some A4s the car will not start while the fault is active

The fault codes

Scanning an affected A4 rack, two codes come up again and again:

• C10AD29 — Motor Position Sensor
• B200049 — Internal Control Module Error

Both are internal to the rack’s own electronics rather than the tie rods, column or wiring — which is why a dealer scan usually ends with a quote to replace the entire rack.

What has failed inside the rack

The failure points sit inside the rack’s integrated steering ECU. The motor position sensor (C10AD29) stops reporting the assist motor’s position reliably, so the module shuts assistance down rather than trust feedback it cannot rely on. Separately, the control module’s electronics fail internally (B200049). Mounted low and exposed to heat, vibration and moisture, it is the sensor and control board — not the mechanical rack and pinion — that give out first on a high-mileage A4.

Repairing your A4 rack

Because the fault is in the electronics rather than the mechanical rack, your A4’s original unit can be repaired at component level instead of replaced. Ours is a mail-in repair-and-return service: you send in the failing rack and steering ECU, our engineers rebuild it in a cleanroom-standard, ESD-safe workshop with circuit-level repair to the sensor and control module, and we return your own unit repaired to meet or exceed OE specification. The known weak points are reinforced, many units come back ready to fit with no coding required, and most remanufactured parts carry a lifetime, unlimited-mileage warranty.

Once your order is complete, print the repair form, note the symptoms and any codes, and pack it in the box with your A4 rack — or send it to us in advance. With it alongside the unit, our engineers can begin the moment your rack reaches the bench. If you aren’t sure the rack is the exact part your A4 needs, our broader electric power steering repair service covers the related steering electronics.