Audi S4 (2011 – 2018) Electric Power Steering Rack

The Audi S4 (B8, 2011–2018) pairs a supercharged V6 with saloon and Avant practicality, and like the rest of the B8 range it relies on an electromechanical power steering rack — assist motor and control module built into the rack, no hydraulic pump. The fault owners meet is electronic: the sensor and control board inside the rack fail while the mechanical rack and pinion remain sound. We repair the S4’s original rack and steering ECU at component level and return your own unit, so its coding is preserved and the weak points are reinforced.

How you’ll know

The unmistakable sign is the red “Steering defective! Do not drive vehicle!” message on the cluster. Read it literally — do not keep driving the S4 once it shows.

• Red “Steering defective! Do not drive vehicle!” warning on the cluster
• Steering going heavy and unassisted, most noticeable at parking and low speeds
• Steering that no longer self-centres after a turn
• The warning starting intermittently before it stays on permanently

The fault codes

When the S4 rack is scanned, two codes recur:

• 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 loom — which is why a fault-code read rarely moves a main dealer beyond replacing the whole rack.

The real point of failure

The weak points sit inside the rack’s integrated steering ECU. The motor position sensor (C10AD29) stops reporting the assist motor’s position reliably, so the control module shuts the system down rather than act on data it cannot trust. Separately, the control module’s electronics fail internally (B200049). Heat and vibration wear out the sensor and control board over time — the mechanical rack and pinion are usually still sound.

Repairing your S4 rack rather than replacing it

Because the fault is in the sensor and control electronics, your S4’s original rack can be repaired at component level rather than replaced with a full new assembly. Ours is a mail-in repair-and-return service: our engineers carry out circuit-level board repair on the sensor and control module, then program and calibrate the unit with dealer-level diagnostic tools before returning your own rack — repaired to meet or exceed OE specification with the weak points reinforced. Most remanufactured parts carry a lifetime, unlimited-mileage warranty, and keeping your original rack means no matching against the B8 chassis and no lost coding. Because the S4 is used across saloon and Avant as an everyday car, keeping downtime short matters — repairing the rack you already have avoids the delay of sourcing a replacement and coding it to your specific vehicle.

After checkout, print the repair form, add your details and the fault the car has shown, and include it in the box with your S4 rack — you can also send it ahead of the unit. It ensures your rack is logged and ready to work on as soon as it arrives. Should you want to confirm the rack is the right part first, the rest of our electric power steering repair service explains what else we repair.