Removing and installing control unit for fuel tank leak detection — AUDI
Removing and installing control unit for fuel tank leak detection on Audi: 9 steps, engines CADA, CAEB, CALB, CDNB.
The control unit for fuel tank leak detection (J909) sits under the floor on the Audi Q5 (8R, 2008–2017) and the other platform code listed below, behind the centre right underbody trim. It is a short job: the underbody trim comes off, the bracket is released by removing bolts 1 and 3 and nut 4, the electrical connector is unplugged after releasing its retainer catch, and the nuts holding the module are removed so J909 can be lifted off its bracket. There is nothing to adjust. The work is under the fuel system, so the general safety precautions and cleanliness rules apply, and the connector catch must be released properly rather than pulled, as a broken latch leads to intermittent leak-detection faults.
🧭 Before you start
Observe the safety and cleanliness rules, then remove the centre right underbody trim. Unbolt the bracket, release the connector catch and unplug J909, remove its nuts and detach it from the bracket. Install in reverse: bracket on, connector clipped, underbody trim refitted.
Fits: Audi Q5 (8R, 2008–2017); platform code 83
Don't miss
- Release the retainer catch before unplugging the connector; do not lever the housing.
- The module is held on the bracket by nuts 2; the bracket itself by bolts 1, 3 and nut 4.
- Refit the bracket before the centre right underbody trim goes back on.
- As general practice, clear any stored leak-detection fault codes after the module is reconnected.
Written for this job from the workshop steps below · TorqFix editorial.
🔧 Engine codes this applies to
📋 Procedure
- Observe safety precautions .
- Observe rules for cleanliness .
- Remove underbody trim (centre right) General body repairs, exterior66Underbody trim; Exploded view - underbody trim.
- Unscrew bolts (1, 3) and nuts (4) and remove bracket (2).
- Release retainer catch and unplug electrical connector (3).
- Remove nuts (2).
- Detach control unit for fuel tank leak detection J909(item 1) from bracket.
- Install bracket .
- Install underbody trim (centre right) General body repairs, exterior66Underbody trim; Exploded view - underbody trim.
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Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.
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The story behind TorqFix →Workshop data on this page last updated 20 Sep 2026.