Audi A4 B6 Comfort Control Module Faults: Common Failures and Repair
The comfort control module (also known as the Komfortsteuergerät or J393) in the Audi A4 B6 is responsible for managing central locking, interior lighting, electric windows, mirror adjustment and the convenience open/close function. When it fails, several of these systems stop working simultaneously — often in confusing combinations that can point straight at this one module if you know what to look for.
What Exactly Does the B6 Comfort Module Do?
Think of it as the nerve centre for cabin convenience electronics. It sits behind the dashboard or in the driver’s door area depending on the variant, and it communicates over the CAN comfort bus with the central locking, window regulators, interior lights and the key/transponder system. A lot happens through this single unit — which is exactly why its failure tends to produce a scattered, hard-to-read symptom list.
On the B6 platform (2000–2004), water ingress is by far the leading cause of failure. The module sits in a location that can get damp from a blocked windscreen drain or a leaking plenum chamber. Corrosion on the PCB kills the module slowly, sometimes over months, before it dies completely.
Common Symptoms of a Failing A4 B6 Comfort Module
- Central locking operates intermittently or not at all from the remote or interior button
- One or more electric windows stop responding or move very slowly
- Interior lights stay on permanently or don’t come on at all
- The convenience open/close function (hold unlock to open windows) stops working
- Mirror fold or adjustment stops responding
- Random fault codes stored in the gateway/body electronics scan
- Battery drain overnight — the module staying active and drawing current
What throws people off is that some of these symptoms come and go. On a cold morning everything works; after rain it falls apart. That’s the moisture expanding and contracting on the corroded solder joints. Classic water-damaged comfort module behaviour on this generation. For comparison, see Audi A4 B6 Comfort Control Module Faults: Common Failures and Repair.
Common Fault Codes for the A4 B6 Comfort Module
| Fault Code | Description |
|---|---|
| 01277 | Comfort system control module — malfunction |
| 01044 | Control module incorrectly coded |
| 00907 | Immobilizer — no signal / communication fault |
| 01176 | Central locking — open circuit or no signal |
| 00932 | Supply voltage — too low (module not powering correctly) |
| 01325 | Convenience closing — electrical fault |
Code 01277 on its own, or alongside 01044, almost always means the module has failed or lost its coding. Don’t just recode without verifying supply voltage and ground connections first — a bad ground can cause the same codes without the module actually being faulty.
Diagnostic Steps
Start with a full VCDS or ODIS scan on the convenience/body channel. Check that you’re actually reaching the module — if the scan can’t communicate with J393 at all, that tells you more than any stored code. Next, pull the module and visually inspect for corrosion or moisture damage on the connector and PCB.
Verify ground point G75 (usually located on the A-pillar area) is clean and tight. A corroded ground here causes phantom comfort module faults that mislead even experienced technicians. Also check fuse SC16 in the fuse box under the dash — the comfort circuit runs through this.
If the module communicates but shows erratic behaviour, try a fresh coding session. If coding fails or won’t hold, the module is almost certainly gone internally.
Common OEM Part Numbers — Audi A4 B6 Comfort Module
| OEM Part Number | Notes |
|---|---|
| 8E0 959 433 AH | Common B6 comfort module variant, 2001–2004 |
| 8E0 959 433 BH | Later B6 revision, updated firmware |
| 8E0 959 433 M | Early B6 production, 2000–2002 |
| 8E0 959 433 P | Mid-series replacement, widely available used |
| 8E0 959 433 S | Variant for cars with convenience package |
Always cross-reference the full part number on the original module before ordering. The suffix letters matter — different variants carry different software and are not all interchangeable without recoding. A tested used OEM module matched to the correct suffix and recoded with VCDS is the most cost-effective fix for most owners. A related diagnostic guide is When the Audi A4 B6 Comfort Module Causes Central Locking Problems.
Affected Vehicles
- Audi A4 B6 (8E/8H) — all bodystyles (saloon, estate, cabriolet), 2000–2004
- Audi A4 B7 (8E) — shares the same comfort module family; early B7 (2004–2005) uses B6-spec units
- Seat Exeo (derived from B6 platform) — uses compatible module variants
The B6 cabriolet (8H) is particularly prone because the hood drainage can dump water directly toward the module location. If you’re buying a used B6 cabriolet, checking the comfort module function before purchase is non-negotiable.
Repair vs Replacement — What Makes Sense?
Professional electronics repair shops can rework the PCB on a water-damaged comfort module — reflowing solder joints, cleaning corrosion and replacing damaged ICs. This costs roughly €80–120 in labour and is worthwhile if you can’t source a correctly coded replacement easily.
However, a tested used OEM module with matching part number suffix, precoded or supplied with coding data, is usually the cleaner fix. Labour to swap and recode is under an hour. New OEM modules from Audi are still available but are priced significantly higher — usually not justified on a B6-age vehicle unless you’re doing a full restoration.
FAQ
Why does my Audi A4 B6 central locking work sometimes but not others?
Intermittent central locking on the B6 is one of the most common signs of a failing comfort control module (J393). Moisture on the PCB causes the module to malfunction inconsistently — it tends to be worse after wet weather or temperature changes. Scanning with VCDS for codes in the comfort module channel is the right first step. For additional context, read Audi A4 B6 Immobilizer and EWS Faults: Diagnosis and Repair Guide.
Can I swap the comfort module myself on an A4 B6?
The physical swap is straightforward — usually a few screws and a connector. The critical step is coding the replacement module to your car using VCDS or ODIS. Without correct coding, the module will either not function or trigger fault codes. If you don’t have access to the software, a workshop can recode it in 15–20 minutes for a small fee.
Does a used comfort module from another A4 B6 need coding?
Yes, always. The module stores vehicle-specific configuration — central locking type, equipment options, convenience functions. A used module from a donor car retains the donor’s coding and must be recoded to your car’s specification. The part number suffix must also match, as different variants carry different base software.
What causes the Audi A4 B6 comfort module to fail?
Water ingress is the primary cause on B6 models. A blocked plenum drain or windscreen seal failure allows water into the cabin and onto the module. The result is corrosion on the PCB solder joints and connector pins. Electrical overvoltage from a failing alternator can also damage the module, though this is less common.
How do I find the correct OEM part number for my B6 comfort module?
The original part number is printed on a sticker on the module body itself. It follows the 8E0 959 433 XX format where the suffix letters define the variant. You can also find it via the VIN in ETKA (Audi’s parts catalogue) or by asking a dealer to look it up. Always match the full number including suffix when sourcing a replacement.
Find tested OEM electronic parts and modules at:
https://giantparts.eu/
