Put the Electronic Parking Brake into Service Mode

Last updated: June 11, 2026

The BMW 3 Series (G20, 2019–Present) uses an electromechanical parking brake with electric motors mounted directly on the two rear calipers, replacing the old cable mechanism. Because those motors hold the rear pistons, a rear pad change starts not with a wind-back tool but by putting the EPB into service (maintenance) mode so it retracts the pistons electronically. There is no accelerator-and-switch owner sequence on the G20 — it is a tool-led job, with a manual fallback for the toolless.

What service mode is and why the G20 needs it

Each rear caliper carries a geared motor that drives the parking-brake piston. With the car live, that motor clamps the piston and resists being pushed back. Service mode commands both rear motors to wind fully open and locks the EPB out so it cannot re-apply while your hands are at the caliper. Only then can the pistons be compressed and the new pads fitted.

Retracting the rear calipers on the G20

Park on level ground, chock a front wheel, and connect a battery charger — the motors draw current and low voltage can abort the cycle. Then pick a route:

1. Scan-tool route (recommended). Plug a BMW-capable tool into the OBD port: BMW ISTA / Rheingold is the factory option, and consumer tools such as BimmerLink, Foxwell or a Schwaben/Autel EPB unit also carry the function on the G20. Open the parking-brake service function and run service / install position. You’ll hear the rear motors whir as the pistons retract.
2. Manual route (no tool). Confirm the EPB is released, unbolt the actuator motor (two Torx screws) from the back of each rear caliper, insert a T45 Torx bit into the splined spindle and turn it clockwise until it stops to wind the piston in. Refit the motors before driving.

With the pistons home, compress them fully, fit the new pads and refit the caliper.

Never force the pistons back by hand

Never compress the G20’s rear EPB pistons with a clamp or wind-back tool while the actuator is attached. They are electromechanical — forcing one back through its motor shears the internal plastic gearing and destroys the caliper. Retract the piston electronically in service mode, or only ever by turning the spindle clockwise with the actuator removed. If a piston feels solid, the car is not in service mode — stop and re-run the routine instead of forcing it.

Exit, CBS reset and bed-in

Once the pads are in and the wheels back on, end service mode with the tool (or pump the brake pedal firmly several times then apply the EPB switch once) so the motors re-clamp to the correct air gap. Pump the pedal until firm before moving the car. While the tool is connected, open the Condition Based Service (CBS) section in ISTA/BimmerLink and reset the rear-brake counter so the dash stops counting the old pads — note the in-car iDrive menu often won’t reset rear pads on its own, which is why a tool is the dependable path. Then bed the pads in: several firm slow-downs from about 30 mph with cooling between them, and check the parking brake holds on a slope.

Frequently Asked Questions

Can I reset the rear-pad CBS from the iDrive screen? Often not — on the G20 the in-car CBS reset frequently won’t clear the rear-brake item, so plan to reset it in ISTA or BimmerLink while you have the tool connected.

Can I do the job without any tool? Yes, by the manual route — release the EPB, unbolt each rear actuator and wind the spindle in clockwise with a T45 Torx. You’ll still want a tool to reset the CBS reminder cleanly.

Do the pistons screw in or push straight? The rear EPB pistons wind in clockwise; they don’t push straight like the fronts. With the actuator off, turn the spindle clockwise on each side.

Service mode quit partway — why? Usually low battery voltage. Put the G20 on a charger and retry; the EPB motors need a strong 12 V supply.

If the dash throws a brake or EPB fault code while you work, decode it first on our sister site autodtcs.com.