Put the Electronic Parking Brake into Service Mode

Last updated: June 12, 2026

The Mercedes A-Class (W177, 2018–Present) uses a true electric parking brake (EPB), not a foot pedal or a lever. A small electric motor on each rear caliper clamps the pad against the disc, and that motor also drives the caliper piston outward. Before you touch the rear pads you have to drive that motor back electronically — either through the instrument-cluster workshop menu or with a diagnostic tool. Forcing the piston back by hand will strip the spindle inside the caliper.

This guide explains how to put the W177 rear EPB into the service (fitting) position so you can change the rear pads, and how to exit and bed in afterwards.

Which parking brake does the W177 have?

Every W177 A-Class — hatchback and saloon, A180 through A45 S AMG — left the factory with a pushbutton electric parking brake. The switch sits low on the dashboard left of the steering column. There is no cable, no ratchet lever and no foot pedal. Because the parking-brake function is integrated into the rear caliper itself (an electric motor-on-caliper design), the rear pistons cannot be wound or pushed back by hand the way an older cable-caliper can. The clamping motor must be commanded to the open/service position first.

Put the rear EPB into the service position

You can release the W177 EPB for pad replacement either from the cluster workshop menu (no tool) or with a generic OBD EPB scan tool. The cluster method:

1. Switch the ignition to position 1 (on, engine off — do not press the brake pedal or the start button to crank).
2. Close all doors, the bonnet and the glovebox — the menu will refuse to run if anything reads as open.
3. Set the central display to show the total odometer reading.
4. Press and hold the telephone/hang-up button and the OK button on the steering wheel together for about five seconds until the workshop menu opens.
5. Scroll to Brake Pad Replacement (Fitting Position), press OK, then confirm. You will hear the rear EPB motors run as the spindles retract.

With a tool, plug into the OBD port under the dash, select the W177/EPB rear-brake function and run “service mode” or “open caliper for pad change.” Mercedes XENTRY does the same and additionally lets you re-adapt the parking-brake travel afterwards. Once the EPB is fully retracted, the hydraulic piston still needs winding back with a piston tool to make room for the thicker new pads.

Critical warning

Never force a true EPB piston back by hand, with a clamp or with water-pump pliers. The W177 caliper has a threaded spindle driven only by its motor; pushing against it shears the gears and you will replace the caliper. Always retract it electronically through the cluster menu or a tool. (Note: this is the opposite of an older foot-brake or cable caliper, where the piston genuinely does wind back by hand — the W177 does not have that type, so do not apply that habit here.)

Exit service mode and bed in

Fit the new pads, wind the hydraulic piston home, and reassemble the caliper. Exit the cluster menu (or run the tool’s “close/calibrate” step) so the EPB clamps back to its normal travel — in the cluster you press OK again to take it out of fitting position. With the car still stationary, pump the brake pedal several times until it goes firm so the pistons seat against the new pads. Apply and release the EPB switch a few times and confirm the dash warning clears. Finally bed the pads in: from a safe speed make six to eight moderate stops, then a few firmer ones, avoiding a hard stop from high speed on cold new pads.

Frequently Asked Questions

Can I change the W177 rear pads without any tool? Yes — the cluster phone + OK workshop menu gives you the Fitting Position with no scan tool. A generic OBD EPB tool is a reliable alternative if the menu does not appear on your trim.

Why won’t the workshop menu open on my A-Class? The most common cause is an open door, bonnet or glovebox, or the display not showing the odometer. The ignition must be on with the engine off, not cranking.

Do the front pads need this procedure too? No. The EPB only acts on the rear axle, so the front pads are a normal hydraulic-piston wind-back with no electronic step.

The parking-brake light stayed on after the job — what now? Take the EPB out of service mode (exit the menu or run the tool’s close step), pump the pedal firm, then cycle the EPB switch. If it still shows, an EPB re-adaptation in XENTRY usually clears it.

Is the A45 AMG any different? The AMG uses larger calipers but the same motor-on-caliper EPB and the same service-mode procedure.

If a brake or EPB fault code is logged on your A-Class, you can look up what it means on autodtcs.com before you start the job.