Mercedes ML W163 Door Locks Cycle Rapidly (Machine Gun Locks): Cause and Fix

Last updated: October 28, 2026

In this guide (5 sections)

1. Temporary Fix: Disable Automatic Locking
2. What Causes Machine Gun Locks
3. Door Lock Actuator Part Numbers
4. How to Replace the Door Lock Actuator on the ML W163
5. Confirm the Faulty Door Before You Open a Panel

Are the door locks on your Mercedes-Benz ML moving up and down rapidly? This is known as the machine gun locks problem. It happens because the actuator in one of the doors is defective: the plastic tappet plate inside the actuator has broken. You can replace the whole actuator or the broken part inside it. The videos at the end of this article show the repair. In the meantime, you can disable automatic locking and stop the rapid locking and unlocking.

Estimated repair cost: $300 to $400 at a shop. If you do it yourself, you are looking at under $200.

Parts: You can get them from these sellers for much less than the dealer.

Affected models: W163 ML-Class, 1998 to 2005: ML230, ML270 CDI, ML320, ML350, ML400 CDI, ML430, ML500 and ML55 AMG.

Temporary Fix: Disable Automatic Locking

The ML locks the doors automatically once you are driving at about 9 mph (15 km/h). With automatic locking switched off, the car stops trying to lock the doors on its own, which stops the cycling while you drive.

• Turn the key to position 2, so all the cluster lights are on. Don’t start the car yet.
• Press and hold the unlock button on the center console for at least 10 seconds. This switches automatic locking off. To switch it back on later, do the same with the lock button.

What Causes Machine Gun Locks

The actuators in the individual doors get damaged and jam, so they no longer respond when the motor tries to lock or unlock the door. When you lock or unlock with the key fob or the dash button, the system retries the action several times. Because the micro switch in the damaged door never reports a locked or unlocked status to the All Activity Module (AAM), the AAM unlocks and relocks all the doors repeatedly, waiting for every door’s micro switch to report locked.

Solution: Replace the door lock actuator in the faulty door, and the locks will work normally again.

You can get the door lock actuator for a fraction of the dealer price from Amazon; see here.

Door Lock Actuator Part Numbers

• Late W163, right rear: 163 730 28 35
• Early W163, left front (driver side): 163 720 25 35
• Late W163, left rear: 163 730 27 35
• Late W163, right front: 163 720 32 35

Early and late W163 actuators differ, so check the part number on your old actuator or confirm by VIN before you order.

How to Replace the Door Lock Actuator on the ML W163

1. Find the door with the broken actuator.
   • Manually unlock all the doors, then lock them. One of them will stay unlocked.
   • Manually lock all the doors, then unlock them. One of them will stay locked.
   • If all four doors work properly, check the liftgate.
2. Remove the cover from the door handle with a flat screwdriver. Behind it you will see two Phillips screws.
3. Remove the two screws inside the door handle.
4. Remove the plastic SRS logo, then unscrew the last screw under it.
5. The door panel is held in place with push in clips. Pry off the door panel.
6. Unplug the wire for the lower door lamp.
7. Disconnect the other wires. One is for the door lock, and the other goes to the speaker.
8. Roll the window up.
9. Find the hole on the edge of the door, in line with the outside door handle. It is covered by a rubber drain seal. Use a T27 Torx to loosen the bolt inside it. You do not need to remove it, only loosen it enough to release the plastic cap on the outside door handle.
10. Remove the plastic cap from the outside door handle.
11. Carefully slide the rest of the door handle back, toward the rear of the car.
12. With the handle off, you will see two more bolts. Loosen them, but do not remove them.
13. Carefully peel back the door moisture barrier.
14. Remove the door latch. It is held by two Torx bolts.
15. Pull the old actuator out and install the new one. This is the tricky part. Don’t bend the window guides; if you do, set them back to their proper position, or the window will not run smoothly.
16. Reassemble everything in reverse order.

Confirm the Faulty Door Before You Open a Panel

The AAM stores the fault for the door that never reports locked, and its live data shows the lock status of each door, which pins down the bad actuator before you take a panel off. After the repair, clear the stored codes and check that every door reports locked. The UCAN-II Pro reads every module on the car, including the body control modules, and shows live data, so you can do both from the OBD port. If the locks are dead rather than cycling, check the central locking fuse in the W163 ML fuse chart first. For the bouncing lock pin on other Mercedes models, see why the Mercedes door lock pin bounces up and down.