Audi A6 C5 Comfort Control Module Faults and Repair Guide
The comfort control module (Komfortsteuergerät) in the Audi A6 C5 is a compact but essential unit that manages central locking, electric windows, interior lighting, the luggage compartment lid and — on some variants — the sunroof and heated mirrors. When it starts to fail, the symptoms can look like a completely random electrical gremlin rather than a single clear fault, which makes diagnosis frustrating if you don’t know what you’re looking for.
Quick Answer
The Audi A6 C5 comfort control module (part of the convenience system, sometimes called the BCM or J393) controls central locking, electric windows, interior lighting and related comfort features. Common failures include water ingress into the module causing short circuits, failed window regulators being falsely blamed, and door-locking systems that stop responding intermittently. Replacement with a tested used OEM unit and correct coding is the most cost-effective repair in most cases.
What Does the Comfort Module Actually Do?
On the C5 platform — which covers the A6 from 1997 through to 2005, including the Allroad and S6 variants — the comfort control module sits under the dashboard on the driver’s side or behind the driver’s door panel depending on production year. It communicates over the CAN bus and the older K-line protocol, collecting inputs from door switches, the remote key receiver, the ignition, and individual window and locking motors.
The module handles anti-pinch protection for the windows, one-touch operation, convenience unlocking logic, and interior lighting delay after you exit the vehicle. It also stores fault events that can be read with VCDS or a compatible diagnostic tool. When this unit develops an internal fault — usually from age, vibration or water damage — several of these functions can drop out simultaneously or behave erratically. For comparison, see Audi A6 C5 Comfort Control Module Faults: Common Failures and Repair.
Symptoms: How a Failing Comfort Module Presents
- Central locking operates from the key fob but not from the interior door button, or vice versa
- Windows drop on their own or refuse to auto-close, even when the car is parked
- Interior lights stay on after closing doors, or don’t come on at all
- One or more doors no longer lock or unlock with the rest
- The remote key range becomes very short — often only works when standing directly next to the car
- Rear windows stop responding while front windows still work, or one corner stops entirely
- Luggage compartment lid release stops working from the button on the dash
A common workshop mistake with C5 A6s is blaming the window regulator or the door lock actuator first. Before replacing mechanical components, always read the comfort module’s own fault memory. Nine times out of ten the module is logging internal supply faults or CAN communication errors that point straight back to itself.
Common Fault Codes
| Fault Code | Description |
|---|---|
| 01044 | Control module incorrectly coded — often appears after battery disconnect |
| 00588 | Central locking — implausible signal from one or more door contacts |
| 01176 | Comfort system — no communication with comfort control module (J393) |
| 00290 | Electric window motor, driver side — open circuit or over-current |
| 00955 | Anti-theft alarm — comfort system not responding |
| 01116 | Supply voltage — too low or intermittent at comfort module connector |
Root Causes — Why the Module Fails
The most destructive enemy of the C5 comfort module is water. The sunroof drain tubes on these cars are notorious for blocking with debris, and when the water backs up it often finds its way into the A-pillar and down behind the dashboard trim. The module connector can sit in a damp environment for months before anyone notices — by which point the PCB inside has corroded at the solder joints on the relay section or the voltage regulator.
Age-related dry solder joints are the second most common cause, particularly on high-mileage cars from the early 2000s. Vibration over many years causes hairline cracks to develop at the joints for the relay pins that drive the central locking circuit. Reflowing the board often fixes this, but the repair doesn’t always last long on a module that’s already 20 years old.
Finally, some failures come from a previous owner’s attempt to fit an aftermarket alarm or remote-start kit. Incorrect wiring into the central locking circuit can send reverse voltage into the module, burning out the transistors on the locking output stage.
Common OEM Part Numbers
These part numbers cover the J393 comfort control module across C5 A6 production years. Always cross-reference your 17-digit VIN before ordering, as the correct coding depends on the exact vehicle specification. A related diagnostic guide is Audi A6 C5 Climate Control Unit Faults: Diagnosis and Repair Guide.
- 4B0 962 258 A — A6 C5 saloon/avant, early production (1997–2001)
- 4B0 962 258 B — revised variant, fits most 2001–2004 C5 models
- 4B0 962 258 C — late C5 and some C5 Allroad applications
- 4B0 962 258 D — S6 C5 and higher-specification comfort variants
- 4B1 962 258 A — right-hand-drive market specific variant
- 4B0 962 258 — base reference number, unfitted (blank) unit for coding
Affected Vehicles
The C5 platform spans a wider range than many owners realise:
- Audi A6 C5 saloon and Avant, 1997–2005, all engine variants
- Audi A6 C5 Allroad Quattro, 2000–2005
- Audi S6 C5, 1999–2004
- Some late C5 RS6 variants share the same module reference
Vehicles built between 2000 and 2003 seem to show the highest failure rate in workshop records, likely because those cars are now over 20 years old and the original solder joints are at the end of their service life. Facelift C5 models (2001 onward) have a slightly revised module with improved relay specifications, but they are not immune.
Repair or Replace?
Electronic repair specialists can reball or reflow the PCB, and in the case of water damage they can clean and re-pot the board. However, if the comfort module has been wet for a long time, corrosion on the multi-pin connector itself causes resistance that a repaired board can’t compensate for. In those cases a tested used OEM replacement is the cleaner solution — provided it is correctly coded to the vehicle using VCDS adaptation channels.
Blank new modules are available from Audi but they carry a significant cost penalty. A tested used OEM unit from a C5 donor car, matched to the correct part number and adapted with dealer-level diagnostics, typically brings costs down to a fraction of the price while delivering the same result.
FAQ
Can I drive an Audi A6 C5 with a faulty comfort control module?
Yes, in most cases the car remains drivable. Central locking may not work fully and the windows may behave oddly, but the engine management system is separate. That said, if the anti-theft alarm system starts triggering randomly due to the comfort module fault, it can prevent starting — so it’s worth diagnosing early rather than waiting. For additional context, read Audi A6 C5 Allroad Air Suspension ECU Faults Diagnosis Guide.
Does replacing the comfort module on an A6 C5 require coding?
Yes, always. The replacement module needs to be adapted to the vehicle using VCDS or an equivalent VAG diagnostic tool. Without correct coding, central locking sequences, anti-theft arming logic and window one-touch operation will not function correctly. The coding process takes about 15 minutes with the right software.
Where is the comfort control module located on the Audi A6 C5?
On most C5 A6 models the J393 module is located behind the driver’s side lower dashboard trim, close to the A-pillar. On some production variants it may be positioned in the door sill area or behind the steering column trim panel. Removing the lower dash trim exposes the module and its two main connectors.
What is the difference between the comfort module and the central locking pump on the C5 A6?
Earlier C5 models used a vacuum-based central locking system with a separate pump; the comfort module controls the signals that operate that pump. Later C5 models switched to electric lock actuators in each door. If your car has a locking pump, check the pump and its hoses before suspecting the module — a blocked vacuum line gives very similar symptoms to a module fault.
Is a used comfort module from a different A6 C5 safe to fit?
Yes, as long as the part number matches your vehicle specification and the unit is tested before fitting. The module stores coding data that links it to the original car’s immobiliser profile, so after fitting it must be re-adapted using diagnostics. A tested OEM unit verified to be fault-free before shipping is the safest and most reliable option for this repair.
Find tested OEM electronic parts and modules at:
https://giantparts.eu/
