2B57

What Code 2B57 Means

Code 2B57 points to a failed throttle actuator on BMW S65 and S85 engines. These engines run individual throttle bodies, with each cylinder bank driven by its own actuator that sets throttle plate position. When the actuator fails, the DME (engine control unit) stores code 2B57 and puts the engine into limp mode to prevent further damage.

Actuator failure has several causes, including worn plastic gears inside the unit or electrical faults. The mileage at which it fails is unpredictable and varies widely. The system gives no clear warning, so the failure usually comes out of nowhere.

Symptoms

• Engine drops into limp mode — the main sign that something serious has failed.
• Codes CDC0, 2B21, and/or 2B57 appear — these codes often show up together and point to a throttle problem.
• Engine may run slightly rough — from incorrect throttle plate control.
• Usually no warning signs — throttle actuators often fail suddenly, with no symptoms beforehand.

Diagnosis and Repair

When code 2B57 and the related CDC0 or 2B21 codes show up, run diagnostics with ISTA or INPA to confirm the throttle actuator fault.

Repair options for S85 throttle actuators:

1. Replace the gears with a repair kit — buy a throttle actuator repair kit with 4 gears to replace the gears inside both actuators. This works if worn plastic gears are the cause.

1. Replace the actuators as complete units — if the actuators failed for other reasons, such as an electrical fault, the repair kit alone won't help; you may need two new actuators. Replacing both at the same time is the usual recommendation.

Labor time:

• The job takes roughly 2–3 hours for an experienced mechanic and up to 4–5 hours for less experienced DIYers.

Important notes:

• When replacing the actuators, replace both at the same time to avoid a repeat failure.
• After the repair, run a throttle adaptation with BMW diagnostic equipment (ISTA).

Secondary Damage

Worn gears are suspected of causing constant adjustments that eventually overheat the electronics. That can kill the electrical side of the actuator and force replacement of the whole unit. Ignoring the fault and driving in limp mode can make the damage worse and lead to a more expensive repair.