SEAT Leon rear centre brake light not working – LED module, fuse, wiring, Hella/Valeo options

User question

seat Leon rear centre light not working

Artificial Intelligence Response

Direct answer to the question

• The rear-centre (high-level/third) brake light on a SEAT Leon usually fails because of (a) loss of supply/ground at the tailgate connector, (b) a blown fuse or defective brake-light switch, or (c) an internal fault in the sealed LED module (dry solder joints, open LEDs, or water damage).
• Work methodically: verify the other brake lights, check the relevant fuse, measure 12 V at the lamp connector with the pedal pressed, and if voltage is present replace or repair the high-level lamp assembly.

Detailed problem analysis

1. Confirm the symptom
   • Have an assistant press the brake pedal; note whether the left/right brake lamps operate.
   • If ALL brake lights are out → common fault (fuse, brake-light switch, BCM).
   • If only the centre lamp is out → fault is in its dedicated wiring or the lamp itself.

2. Electrical path overview (Leon Mk2/1P, Mk3/5F, Mk4/KL – hatch & ST)
   • Battery → brake-light fuse (F13/F23 depending on MY) → brake-light switch → Body-Control Module (BCM) → tailgate harness → CHMSL connector → LED driver PCB → LED strings → chassis ground.
   • BCM monitors current; open-circuit LEDs or wiring will log a “brake-light fault” DTC and can extinguish the driver.

3. Fuse & brake-light switch
   • Locate the brake-light fuse in the cabin fuse-box (left end of dash, fuse map in owner’s manual). Test with DMM; replace only with identical amperage.
   • If all lamps are dark and the fuse is intact, check the pedal switch (3- or 4-pin) — the switch can be tested in situ with a meter (should change from open to <0.2 Ω when pedal is pressed).

4. Accessing the high-level lamp
   • Hatch / ST: open tailgate, remove the upper plastic trim (trim-clip tool, Torx T20 if fitted).
   • Two spring clips retain the module; push the tabs and slide the lamp rearwards. Disconnect the 2-way plug. No spoiler removal is required on Mk3/5F.
   • Estate/ST spoiler style: lamp is clipped into the spoiler; release with a non-marring plastic lever.

5. Supply/ground test
   • Multimeter to DC 20 V.
   • Black probe to bare chassis metal, red probe to supply pin.
   • Pedal pressed → 12–14.4 V must be present; ground pin ≈ 0 Ω to chassis.
   • 0 V supply → trace back to tailgate gaiter: wiring often breaks inside the rubber boot due to flexing (typical colours: grey/black = +, brown = GND). Repair with solder & adhesive heat-shrink or replace mini-loom.

6. Lamp internal repair (if 12 V present but lamp dark)
   • Module is LED-based from MY 2005 onward. Carefully prise lens (softened with warm air) – beware of sonic-welded edges on later units.
   • Common failures:
   – Dry/cracked solder joints on LED legs or connector header → re-flow with fine-tip iron and 60/40 SnPb solder.
   – Open-circuit LED in a series string → entire strip dark. Identify with DMM diode-test; replace with 620–630 nm red LED (SMD 3528/2835 20 mA for Mk2, HE-SMD for Mk3).
   – Burnt current-limiting resistor (typically 47–150 Ω 0.25 W) → replace.
   – Water ingress → scrub board with IPA, dry, and re-seal housing with automotive silicone.

7. Replacement option
   • OE part numbers:
   – Mk2/1P hatch ‑ 1P0 945 097A
   – Mk3/5F hatch ‑ 5F0 945 097D
   • Quality aftermarket units from Hella/Valeo cost €35–€60 and are plug-and-play; this is faster/cheaper than board-level repair for most owners.

Current information and trends

• Since 2020 the Leon Mk4/KL uses a CAN-controlled full-width LED bar; individual LED failure triggers a BCM fault and requires complete lamp replacement – no serviceable parts.
• EU Regulation 48 now mandates continuous lamp monitoring; expect tighter diagnostics and higher LED integration.

Supporting explanations and details

• LED chain mathematics: if six red LEDs (Vf≈2 V at 25 mA) are in series, total Vf ≈ 12 V. With system supply 14 V the resistor R = (14 V – 12 V)/0.025 A ≈ 82 Ω (E-series 82 Ω).
• Wiring-boot failures: every tailgate cycle flexes the loom ≈ 50 mm; after ~80 k cycles copper work-hardens and strands break — most frequent on brown (ground) and grey/black (stop-lamp feed).

Ethical and legal aspects

• A non-functional CHMSL fails MOT/NCT/TÜV and compromises rear-end safety.
• Do not bypass fuses or defeat BCM monitoring.
• Dispose of damaged LED modules as WEEE electronic waste.

Practical guidelines

1. Tools: trim-clip set, Torx T20, multimeter, soldering iron (15-25 W), heat-shrink, dielectric grease.
2. Best practice: always isolate battery before soldering on vehicle wiring; reconnect and clear fault codes with OBD-II scanner afterward.
3. Seal repaired lamp with non-acetic RTV; test for condensation by 15 min heat-gun / cold-spray cycle.

Possible disclaimers or additional notes

• On some early Mk2 models the CHMSL shares the same filament as the rear fog-lamp; verify wiring diagram if symptoms differ.
• Housing plastic becomes brittle with age; prising too forcefully breaks locating tabs – work warm and slowly.

Suggestions for further research

• Investigate flexible-PCB LED assemblies with conformal coating to withstand tailgate flex.
• Study automotive high-power LED driver ICs (e.g., TI TPS9261x) for retro-fit upgrades.
• Review UNECE R7/R48 lighting regulations for future design work.

Brief summary

Check the fuse and brake-light switch; if they are good, probe the centre-lamp connector. No voltage → repair tailgate wiring; voltage present → the LED module has failed: either re-solder/replace faulty LEDs and resistors or fit a new OE/aftermarket CHMSL. Prompt repair is mandatory for safety and legal compliance.

Disclaimer: The responses provided by artificial intelligence (language model) may be inaccurate and misleading. Elektroda is not responsible for the accuracy, reliability, or completeness of the presented information. All responses should be verified by the user.