Puede el módulo de confort del Mercedes W203 C-Class causar fallo del cierre centralizado

The comfort module — known internally as the Komfortsteuergerät or KG — in the W203 C-Class is the central controller for door locking, electric windows, the interior light delay and several convenience functions. When it develops a fault, the most immediate symptom is usually partial or total central locking failure, but the module can also produce bizarre window behaviour, lights that stay on, or complete loss of remote key response.

What the W203 Comfort Module Actually Controls

The W203 uses a single comfort control unit mounted behind the dashboard on the driver’s side. It receives commands from the door lock switches, the remote key receiver and the ignition signal, then drives the door lock actuators through a relay network. It also manages the interior light cutoff timer, the anti-trap logic on the windows and, on some equipment levels, the rain-closing function for the sunroof and windows.

Because it sits at the centre of so many body functions, a fault in this one module can produce symptoms that look completely unrelated — a window that closes partially and then reverses, a central locking system that only locks the front doors, or interior lights that never extinguish. Chasing these faults across individual switches and actuators is time-consuming if the module itself is the actual problem. For comparison, see ¿Puede el módulo SAM de la Mercedes W203 Clase C descargar la batería durante la noche?.

How the Comfort Module Fails on the W203

Failure is rarely sudden. Most W203 comfort modules develop problems gradually, typically caused by one of three root causes:

Capacitor degradation on the internal power supply board. The module runs constant low-level monitoring even with the ignition off. Over time, electrolytic capacitors dry out, causing voltage instability inside the unit. This often produces the intermittent locking faults that are temperature-sensitive — working fine in summer, misbehaving on cold mornings.
Moisture ingress. Water can reach the module if the windscreen seal leaks or if drain channels behind the dashboard become blocked. Corrosion on the board connectors produces communication errors between the module and the door control units.
Connector pin oxidation. The main harness connector on the module is a multi-way block that carries both power and CAN signals. Oxidised pins cause the module to lose contact intermittently, which the diagnostic system reads as a communication timeout rather than a clear hardware fault.

Diagnostic Fault Codes to Expect

Reading the W203 with a Star Diagnosis (SDS/DAS) tool or a compatible third-party scanner gives a clearer picture than basic OBD readers. The comfort module stores its own fault memory. Relevant codes include:

Código de avería	Descripción
B1000	Control unit — internal supply voltage fault
B1001	Control unit — EEPROM read/write error
B1450	Door locking motor — front left, open circuit or short
B1451	Door locking motor — front right, open circuit or short
B1601	Window regulator anti-trap — calibration lost
U1110	Missing message from instrument cluster via CAN
U1120	Communication fault — interior CAN bus timeout

B1000 and B1001 typically point to the module itself rather than an external wiring problem. U-codes indicate network-level issues which could be the module, a wiring harness fault, or another node affecting the bus. Start by verifying power supply and ground connections to the comfort module before condemning it on U-codes alone.

Testing Before Replacing

Before ordering a replacement module, carry out basic checks. Confirm battery voltage is above 12.4 V with the engine off. Check the 30A fuse for the comfort module in the front fuse box — it is the fuse labeled KG or F30 depending on the year and equipment variant. Inspect the main 26-pin or 32-pin connector on the module itself for pushed-back pins, green corrosion or burn marks.

If the connector is clean and supply voltage is correct but the fault codes persist and recur after clearing, the module board itself is the likely cause. A useful cross-check: connect a working door lock actuator directly to a 12 V supply. If the actuator moves freely, the module is not driving it correctly. A related diagnostic guide is Cómo probar la pasarela CAN de Mercedes W203 C-Class antes de reemplazarla.

Números de referencia de los fabricantes de equipos originales (OEM) pertinentes

The W203 comfort module varies by build date, engine, left- or right-hand drive and equipment level. Common OEM references include:

A 203 820 01 26
A 203 820 02 26
A 203 820 04 26
A 203 820 26 26
A 203 820 27 26

Matching the full OEM number stamped on your original unit is strongly recommended. Comfort modules from the W203 C180, C200, C220 CDI and C320 can differ in software coding even when the part number looks similar. A used replacement from the same equipment specification is the most reliable starting point. If you fit a unit from a different specification, re-coding with Star Diagnosis is required to activate correct functions.

Affected Vehicle Range

The W203 C-Class was produced from 2000 to 2007, covering the facelift (2004 onwards) and pre-facelift variants. Both saloon, estate (S203) and coupe (CL203) use the same comfort module concept, though exact part numbers differ between body styles. Petrol engines from C160 to C320 and diesel variants C200 CDI, C220 CDI and C270 CDI are all affected — the comfort module is not engine-specific, but it is body-style and equipment-level specific.

Preguntas frecuentes

Can a faulty comfort module drain the W203 battery overnight?

Yes, this is a recognised failure pattern. A comfort module that fails to enter sleep mode keeps the interior CAN bus partially active, drawing between 50 and 150 mA continuously. Over one to two days this will flatten a standard battery. If you measure quiescent current above 30 mA with all doors closed and the ignition off, the comfort module is one of the first components to suspect on the W203.

Does a used W203 comfort module need coding after installation?

In most cases yes, although the extent depends on whether the replacement module comes from an identical-specification vehicle. Basic functions like central locking often work immediately without coding, but rain-closing, window anti-trap calibration and remote key pairing usually require a Star Diagnosis session. A module from a different body style will require full variant coding before all functions operate correctly. For additional context, read Qué sucede dentro del inmovilizador EWS del Mercedes W203 cuando falla.

Can I repair the comfort module board rather than replace it?

Board-level repair is possible if the fault is caused by failed capacitors or a corroded connector rather than a failed microcontroller. Specialist electronics workshops can replace the capacitors and clean the board, which is a viable option when the module is difficult to source. However, if the fault codes include EEPROM errors or internal voltage faults pointing to the main processor, board repair becomes unreliable and replacement is the safer choice.

Why does my W203 central locking only lock the front doors?

This is a classic comfort module symptom. The module drives front and rear lock actuators through separate relay outputs. When one relay circuit weakens, the front doors respond but the rear actuators do not receive enough voltage to operate. The problem can also be caused by a failed rear door actuator, so confirm by measuring voltage at the rear actuator connector while pressing the lock button — if voltage is present but the actuator does not move, the actuator has failed, not the module.

Which diagnostic tools work with the W203 comfort module?

Mercedes Star Diagnosis (SDS/DAS/Xentry at the older software level) reads the comfort module correctly and allows coding and actuator tests. Autel MaxiSYS, iCarsoft MB II and Launch X431 with a Mercedes-specific licence also cover the W203 comfort module reasonably well for fault reading, clearing and basic output tests. Generic ELM327 readers do not communicate with this module as it sits on the proprietary interior CAN network rather than the OBD-II diagnostic bus.

Encuentra componentes y módulos electrónicos OEM probados en:
https://giantparts.eu/

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Explora la categoría: Módulos BCM, SAM y de confort