Buying a Used Audi A6 C5 Comfort Module: Five Checks Before You Pay
The comfort module on the Audi A6 C5 — also labelled the Komfortsteuergerät or convenience control unit — manages central locking, electric window operation, interior lighting, mirror folding and in higher-spec cars the tilt and slide sunroof. A failed unit causes a cluster of body electrical faults that look unrelated until you trace them back to a single node on the CAN bus. Before paying for a used replacement, five checks will tell you whether the unit on offer is worth fitting.
Why the Comfort Module Fails on the C5 A6
The C5 A6 was built from 1997 to 2005, and units produced in the early part of that run are now over twenty years old. The comfort module sits behind the dashboard on the driver’s side, in a location that protects it from direct rain but not from condensation. Internal solder joint failure is common, especially on the relay contacts that handle the central locking pump. A secondary failure mode is the LIN bus driver chip, which causes individual door modules to stop reporting their status. Neither failure is visible from the outside — which is exactly why a visual-only inspection of a used unit tells you very little.
Check One — Confirm the Full Part Number Including Suffix
The comfort module for the C5 A6 carries a part number in the 4B0 series. Common references include 4B0 962 258 A, 4B0 962 258 B, 4B0 962 258 C și 4B0 962 258 D. On Allroad C5 variants and cars with the higher comfort package, you may also see 4B0 962 258 E și 4B0 962 258 F. The suffix letter is not a cosmetic difference — it reflects changes to the software calibration, the relay configuration and sometimes the number of LIN bus channels. Fitting a suffix A unit in a car that left the factory with a suffix D will leave the sunroof, folding mirrors or remote window operation non-functional even after coding.
Ask the seller to photograph the label on the unit itself, not just a listing description. Labels are sometimes updated at the factory when a board revision changes, so the printed number on the case is the only authoritative reference. Cross-check it against your car’s original part number, which you can read from the coding block in VCDS or from the label on the original unit. For comparison, see De ce eșuează Modulul de Confort Audi A6 C5: Cauze Principale.
Check Two — Ask Where the Unit Was Removed From
A comfort module pulled from a low-mileage accident-damaged A6 is a very different proposition from one stripped from a flood-damaged car. The module itself will not show obvious water marks unless immersion was severe, but the connector pins may show green oxidation or white mineral deposits. Ask the seller what the donor car’s fault history was. If the answer is “it was working fine” without any detail, that is worth less than a seller who can say the car came in with an airbag fault and the body electrics were unaffected.
When you receive the unit, inspect the multi-pin connector housing under good light. The main connector on the 4B0 unit carries 26 or 32 pins depending on specification. Any pin that shows brown discolouration at the tip, visible corrosion inside the socket or deformation from a previous extraction tool is a risk that will not improve after fitting.
Check Three — Read the Fault Memory if Possible
A seller who has access to a VCDS or OBD interface can read the stored faults from the comfort module before removal. The codes most relevant to a buyer are:
- 01284 — Central locking pump, open circuit or short to ground
- 01036 — LIN bus communication fault, door module not responding
- 01035 — LIN bus timeout, typically the front left or front right door
- 00928 — Access authorisation, relevant if the unit has been through an immobiliser mismatch
- 01290 — Interior lighting, implausible signal
Codes 01284 and 01290 that are stored but not active at the time of removal are less worrying — they may reflect a wiring fault on the donor car rather than a module failure. Code 01036 active at the time of removal means one of the door submodules was not communicating, and you need to know whether that was the door module or the comfort module itself causing the dropout. Code 00928 is a red flag — it suggests the unit was involved in an immobiliser coding procedure that did not complete cleanly.
Check Four — Confirm the Coding Requirement for Your Car
The C5 A6 comfort module requires variant coding after installation. This is not optional and it is not a formality — the coding block tells the unit which equipment is fitted: sunroof type, number of electric windows, whether folding mirrors are present, trailer electrics and the alarm system variant. A unit pulled from a car without a sunroof fitted into a car with a tilt-slide roof will operate the locking correctly but ignore the roof entirely until recoded.
Coding is done with VCDS (VAG-COM) or equivalent. The module does not require a PIN or dealer authorisation to recode on the C5 platform — this is one of the last Audi generations where comfort module swaps were genuinely DIY-friendly in this respect. However, if the car has a factory alarm, the siren synchronisation sequence needs to be run after fitting. Note the coding value from your original unit before removing it, or retrieve it from your scan tool’s session log. A related diagnostic guide is Modul de Confort Audi A6 C5 Defecte: Simptome și Reparație.
Check Five — Test the Unit Before Committing to Installation Labour
If you have the unit in hand before booking the car into a workshop, bench-testing it is possible with a 12 V supply, the correct connector and a short loom section. Most independent specialists who handle VAG work will do a bench power-up for a small fee. The unit should power up, communicate on CAN and report no internal hardware faults within the first thirty seconds. This does not guarantee it will perform perfectly in the car, but a unit that fails bench power-up is definitively not worth fitting.
Affected Vehicles and Platform Notes
The 4B0-series comfort module fits the Audi A6 C5 produced from model year 1997 to 2005, including the Avant estate and the Allroad quattro variant. The Allroad frequently uses a higher-suffix variant due to the additional chassis functions and the different sunroof configuration. The A6 C5 platform is not shared with the Passat B5 in the comfort module — the Passat uses a different control unit from the 3B0/3B9 family. Do not attempt cross-platform substitution between C5 and Passat B5 even where connectors look similar.
OEM Part Numbers for Reference
| Part Number | Typical Application |
|---|---|
| 4B0 962 258 A | Early C5, base specification, no sunroof |
| 4B0 962 258 B | C5 with tilt-slide sunroof, standard doors |
| 4B0 962 258 C | C5 with alarm system, 4 electric windows |
| 4B0 962 258 D | C5 late build, folding mirrors, alarm |
| 4B0 962 258 E | C5 Allroad, air suspension coded variant |
| 4B0 962 258 F | Late Allroad and high-spec Avant, full equipment |
Always verify against the label on the physical unit. Supplier databases sometimes list earlier suffix numbers as compatible when the equipment difference will cause missing functions.
Frequently Asked Questions
Can I fit a comfort module from an Audi A4 B6 into an A6 C5?
No. The A4 B6 uses a different comfort module family with a different connector arrangement and different software architecture. The part numbers are not interchangeable and the connectors will not mate correctly without modification. Stick to 4B0-series units for the C5 A6.
Does the replacement comfort module need to be matched to the VIN?
Not on the C5 platform. Unlike later Audi generations, the C5 comfort module does not store the VIN internally and does not require dealer-level authorisation to recode. Standard VCDS coding is sufficient, provided you have the correct coding value for your car’s equipment level. For additional context, read Modul de Control al Transmisiei Audi A6 C5 Allroad - Codificare După Înlocuire.
My central locking works but electric windows do not after fitting a used unit — why?
This is almost always a coding mismatch. The number of electrically operated windows is a coded parameter. If the unit was pulled from a two-window car (some earlier base models only coded front windows) and your car has four, the rear window control will appear dead. Correct the coding block to match your car’s actual equipment and retest.
Will a comfort module fault cause the alarm to trigger randomly?
Yes, this is a known symptom. If the comfort module loses communication with one of the door submodules on the LIN bus, the alarm interprets the missing status report as an intrusion event and activates the siren. A failed solder joint on the LIN driver circuit inside the module is the most common cause. Before replacing the module, confirm the door modules themselves are communicating correctly — a failed door module produces the same symptom.
How long does it take to fit and recode a used comfort module on the C5 A6?
Removal and refitting is typically one to one and a half hours for an experienced technician — the module is accessible behind the lower dash panel without needing to remove the instrument cluster. Coding takes under fifteen minutes if you have the original coding value. Budget for an additional alarm synchronisation step if the car has the factory siren fitted.
GiantParts supplies tested OEM comfort modules for the Audi A6 C5 with part numbers verified against the label on the unit. All modules are checked for communication function before dispatch and shipped worldwide.
Find tested OEM electronic parts and modules at:
https://giantparts.eu/
Ghiduri diagnostic aferente și piese originale
- Modul de control compresor suspensie pneumatică Audi A6 C5 Allroad - Testare
- Procedura de Testare a Modulului de Control al Suspensiei pentru Audi A6 C5 Allroad
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