PSE · vacuum
The R129 does not lock its doors with electric solenoids. A pump in the trunk pushes and pulls air through colour-coded lines to actuators in the doors, the fuel flap, the trunk, and (on some cars) lumbar bladders. When the pump chatters or never stops, you have a leak. When it never runs, you have power, the IR receiver, or the pump itself.
Trunk, spare-wheel well, in a foam cube next to (not the same as) the hydraulic roof pump. Black plastic, several vacuum nipples, an electrical plug.
Supply manifold to the distribution block. Intake through a small filter that blocks with 30-year-old dust.
No click when you press the key or the dash lock switch: trunk fuse 6, then power at the pump, then the pump. Runs for more than a couple of seconds: leak. Rebuild kits (diaphragm + valves) are cheaper than a new pump.
Near the pump, or further forward along the right-side harness depending on year.
Splits lock (typically yellow) and unlock (typically red) plus a black supply. Colours were not religiously consistent — tag them before you pull anything.
One function dead (fuel flap, but doors work) usually means a line off this block, not a dead pump.
Inside the left door, toward the rear. The vacuum lines pass through the rubber boot between A-pillar and door — the #1 rot point on the car.
Two small tubes in the boot, bundled with the window and lock wiring. Dry-rot here lets the pump run forever and will also take out window Hall wiring when water follows.
Left door does not lock, or locks and immediately unlocks. Pop the boot before you buy an actuator.
Mirror of the left, inside the right door.
Same two-tube boot. Slightly easier to reach on LHD cars.
Same as left. If BOTH doors fail, it is the pump, fuse 6, or a common line — not two actuators at once.
Behind the filler door, in the rear quarter. A tiny pneumatic ram.
A single branch off the lock circuit so the flap locks with the doors.
Flap stuck shut: do not pry the paint off. The emergency release is inside the trunk, right side, usually a yellow loop or a rod. Then replace the ram or the split line.
In the lid or on the latch, depending on year.
Short run from the distribution block.
Lid that will not central-lock, or a latch that breathes and unlatches on bumps. Combined with a dead IR, still check fuse 6 first.
Receivers in the door handles / mirror area on early cars; later cars still use infrared, not radio, for the factory remote. Aim at the handle, not the sky.
Electrical only — the IR unit commands the PSE pump. Power from trunk fuse 6 and engine-bay fuse 8 (logic).
Key fob: cracked solder on the IR LED and tired batteries. Car: a receiver that only works at 10 cm is dying. After a battery change the remote may need the factory re-sync procedure (lock cycle with the key in the door, then press remote).
Centre console / dash, the two-icon lock button.
Electrical request to the PSE unit. If this button works and the remote does not, the pneumatics are fine.
This is your fastest split: button works / remote does not = IR. Neither works, pump silent = fuse or pump. Neither works, pump chatters = leak.
| From | To | Via |
|---|---|---|
| PSE pump | Distribution block | short supply |
| Distribution block | Left door actuator | right-to-left run, then door boot |
| Distribution block | Right door actuator | right door boot |
| Distribution block | Fuel flap | rear quarter |
| Distribution block | Trunk latch | lid loom |