When the Audi A4 B6 Comfort Module Causes Central Locking Problems

The comfort control module in the Audi A4 B6 — known internally as the Komfortsteuergerät — sits at the heart of the vehicle’s body electronics. It governs central locking, electric window operation, interior lighting, and in many configurations the anti-theft alarm logic. When it develops a fault, the symptoms rarely announce themselves cleanly. Instead, owners find themselves chasing what looks like a wiring problem, a faulty door handle, or a dead key fob — when the actual source is a failing module sitting behind the dashboard.

What the B6 Comfort Module Actually Controls

Unlike a basic relay box, the comfort module in the A4 B6 (built approximately 2001–2004) actively manages several interconnected systems. Central locking is the most visible: the module interprets signals from the key transponder, the door handles, and the remote and then drives the locking motors across all four doors. Electric window regulation — including the one-touch up/down function with anti-pinch protection — also runs through this unit. Interior lighting delay, boot release, and mirror folding on equipped models are additional responsibilities.

Because so many functions share this single control unit, a partial failure can produce a confusing mix of symptoms. One door may lock while another does not. The windows might work from the driver’s switch but not from the passenger side. Interior lights might stay on too long or not activate at all. None of these symptoms immediately point to one electronic module — which is exactly why misdiagnosis happens so frequently on this platform.

How Failures Typically Develop

The B6 comfort module fails in a few recognisable patterns. Water intrusion is the most destructive. On early B6 examples the door seal and A-pillar drainage can allow moisture to reach the module, which sits in the driver’s footwell area on many build variants. Corrosion on the connector pins then causes intermittent communication faults — the module might respond normally on a dry day and fail completely after rain.

Solder joint fatigue is another failure mode. The PCB inside the unit uses surface-mount components that develop hairline cracks over time, particularly around the main processor and the relay drivers for the locking motors. This produces exactly the kind of intermittent behaviour that makes diagnosis frustrating — the fault clears itself, only to return weeks later under vibration or temperature stress. For comparison, see Audi A4 B6 Comfort Control Module Faults: Common Failures and Repair.

A less obvious but surprisingly common issue is internal relay failure. The comfort module contains small relays that drive the locking actuators. When these degrade, specific doors may stop responding to lock or unlock commands even though the rest of the system appears functional.

Fault Codes Associated With This Module

Reading codes from the comfort module with VAG-COM (VCDS) or an equivalent OBD tool that supports the full CAN bus on B6 platforms is the first diagnostic step. The following codes appear frequently:

Fault Code	Description
00532	Supply voltage terminal 30 — implausible signal or undervoltage
01218	Central locking pump motor — open circuit or short
00928	Central locking — no communication with module
01196	Comfort module internal fault — general electronics error
00490	Door contact switch — implausible signal (linked to module misread)

Code 00928 in particular — where the central comfort module reports no communication — can point either to the module itself or to a wiring harness fault between the module and the CAN bus. Always verify supply voltage and ground at the module connector before condemning the unit.

Checking the Module Before Replacement

Before ordering a replacement, carry out three checks. First, inspect the module connector for corrosion or moisture. On B6 cars driven in wet climates or with failing door seals, the 32-pin connector on the comfort module often shows green oxidation on the signal pins. Cleaning the connector sometimes restores function temporarily — but the solder damage is usually already done internally.

Second, verify battery voltage at terminal 30 and terminal 15 at the module. A weak connection at either supply rail will cause the module to behave erratically without generating a definitive internal fault code.

Third, use VCDS to check whether the module is visible on the CAN bus at all. If it does not respond to a module scan, the fault is either the module itself or the wiring feeding it — not a downstream component like a door handle or window regulator. A related diagnostic guide is Audi A4 B6 Immobilizer and EWS Faults: Diagnosis and Repair Guide.

OEM Part Numbers for the Audi A4 B6 Comfort Module

The correct part number depends on the equipment level, model year and body configuration. Always cross-reference against the label on your original unit before ordering. Common OEM references include:

8E0 959 433 AQ
8E0 959 433 AR
8E0 959 433 BH
8E0 959 433 BK
8E0 959 433 BL

The suffix letters matter significantly. A module coded for a car with alarm differs internally from one without. Fitting the wrong variant may result in the alarm triggering unexpectedly, or central locking failing to complete its full cycle. Match the suffix from your original unit wherever possible.

Does a Replacement Module Need Coding?

Yes. A used OEM comfort module from another B6 will carry the previous vehicle’s configuration. Before it functions correctly in your car, it must be adapted using VCDS or equivalent VAG diagnostics. This process writes the correct equipment configuration — alarm presence, number of locking zones, window regulator type — to the replacement unit. Without adaptation, central locking may work in a limited mode, or the anti-theft alarm may not arm correctly.

Coding is straightforward for any workshop with VAG-capable diagnostic equipment. It does not require a dealer visit in most cases. The replacement module itself does not need to match the VIN — only the equipment configuration must be written correctly during adaptation.

Affected Vehicles

The Audi A4 B6 platform runs from 2001 to 2004 across saloon, Avant estate and Cabriolet body styles. The comfort module is a shared component across most equipment levels, though Cabriolet variants use a different configuration with additional roof control logic. The B6-based Audi A4 Cabriolet (8H) uses a separate unit. If you own the Cabriolet, verify the module reference carefully before purchasing.

Frequently Asked Questions

Can the B6 comfort module cause the central locking to lock and unlock on its own?

Yes. A failing comfort module can trigger unintended locking cycles, particularly when an internal relay is degrading or a connector pin is intermittently losing contact. This symptom is often mistaken for a faulty key fob or a failing lock actuator. Pulling a live data scan during the event can confirm whether the command originates from the module or from an external input. For additional context, read Audi A4 B6 ABS Control Module Failure: Symptoms and Repair Guide.

My windows stopped working on one side only — is this always the comfort module?

Not necessarily. The comfort module processes the switch inputs and drives the regulator motors, but a failed window switch, a broken regulator, or a damaged wiring loom in the door card can cause the same symptom. Check fault codes in the comfort module first. If the module logs no fault for that window channel, shift attention to the regulator and wiring.

Will a used comfort module from a B6 saloon work in a B6 Avant?

In most cases yes, provided the equipment configuration is identical — same alarm variant, same number of locking zones. The body style itself does not affect the module internally. However, the coding written during installation must reflect the actual vehicle’s equipment, not the donor car’s. Adaptation through VCDS is required regardless.

How do I know if water damage has reached the comfort module?

Open the driver’s footwell and locate the module — typically mounted near the A-pillar. Check the connector for moisture or white residue on the pins. If the connector looks clean but intermittent faults persist after rain, carefully remove the module and inspect the PCB for corrosion tracks or component discolouration. Even minor moisture ingress can corrode hairline traces on the board.

Can the Audi A4 B6 comfort module drain the battery?

A malfunctioning comfort module can prevent the vehicle from entering sleep mode properly on the CAN bus, resulting in a parasitic drain that discharges the battery overnight. If the car suffers repeated flat battery incidents with no obvious cause, measure quiescent current draw after locking the vehicle. A healthy B6 should draw below 50 mA after several minutes. Higher readings with the comfort module active suggest the unit is failing to go into standby.

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