W210 Alarm Module | Location

| Symptom | Likely Culprit | Action | | :--- | :--- | :--- | | Car won't start, lights flash, no siren | Immobilizer / Control module | Access | | Siren screams randomly, even with battery disconnected | Internal battery leak in Siren | Remove wheel liner siren | | Key fob works from 1 inch away only | Dirty IR sensor on door handle | Clean lens (unrelated to module) | | Doors lock/unlock randomly while driving | Faulty PSE pump | Access footwell pump |

Mercedes-Benz W210 alarm modules are VIN-coded to the car. You cannot simply swap one from a junkyard without an SDS (Star Diagnostic System) computer to reprogram it. The siren, however, is plug-and-play (and optional). w210 alarm module location

Shine your flashlight into the cavity you just exposed. | Symptom | Likely Culprit | Action |

The alarm module usually has a part number starting with 210 800... or A 210 820... It will have a multi-pin connector (usually blue or grey). Shine your flashlight into the cavity you just exposed

In most standard W210 models, the alarm control module is integrated into the Pseudo-Security Control (PSE) pump . This multipurpose unit is located underneath the rear seat cushion on the passenger side Lift the rear seat and look for a foam-encased block.

The component you are looking for is technically the (Part No. Typically: A 210 820 05 26 or A 202 820 05 26).

The module is a black, rectangular plastic box approximately 4" x 3" x 2". It has a small external speaker grille (or trumpet-like horn opening) facing downward or toward the fender. It is secured by a single 10mm nut to a threaded stud welded to the body.