Known failure patterns

Named signatures documented in the manual and service bulletins. A signature match short-circuits the triage tree — but still run the confirming static test, still fetch the cited page for the current procedure, and still check the live bulletins index.

Everything here is seeded from published documentation; no invented failure rates. Specs mentioned inline are labeled with the page to verify against — fetch before quoting.

Drivetrain

Paddock-only, both-direction rear clunk/chatter at low speed → Plate-LSD behavior: normal chatter, worn plates, lost preload, or wrong oil. Check: backlash, plate wear, preload, oil spec (Royal Purple 75W-140 per maintenance/fluids.md — verify live; raw-parts.com has listed 75W-90, the manual wins). Don’t confuse a broken-in diff with a worn one — an unloaded diff spins easily by hand by design (tunables/diff-plate-stacks.md). Bulletins: 2025-10-07 Differential Rebuild Upgrade Kit.

Click/tick from a rear corner under turning + load → Outboard CV joint. Bulletin 2025-07-09 Upgraded Outboard CV Joint Hardware published upgraded hardware — check whether the car has it before rebuilding with old parts. Page: maintenance/each-year/rebuilding-axles.md.

Shift system

(All procedures: maintenance/electronics-and-wiring/gcu-debugging.md unless noted.)

False neutrals / missed shifts, both directions, intermittent → Tank pressure first (watch AiM during a shift burst; compressor recovers ~1 psi/sec — verify live), then countershift setting, then mechanical. Start at the page’s “Where to Start” index. Bulletin: 2025-09-12 Compressor TSB.

No shifts, no compressor, all at once → GCU power-supply electrolytic cap (the blue P4 35V cap) — the most common cause after fuse and heartbeat LED are ruled out. Variant: shifts fine then dies completely, full car power cycle recovers it → loose solder joint at the same cap; reflow.

One shift then nothing → Shorted paddle filter cap (logic pin stuck low reads as continuous press). Bypass test confirms in minutes.

One direction weaker / sounds different / big pressure drop per shift → Valve block venting past its seat, or an unseated pin in the valve block’s Amphenol connector — inspect the connector before pulling the block. Shift valve is a four-event service item; overdue service masquerades as failure.

Throttle capped ~50%, no fault codes (Gen2 DBW) → Speed Emulator. Confirm: ~25 mph reported over OBD stationary, rev limit ~6000 RPM in neutral (verify live). Distinct from the Gearshift Sensor Mimic — don’t conflate.

Limp mode + no blip on downshift (Gen2 DBW) → Clutch switch state on the AiM channel; check the neutral switch hasn’t broken off.

Paddles register on LEDs but no blip/cut (Gen2 DBW) → Gearshift Sensor Mimic path (GCU pin 12 PWM → ECU). Serial console: no Writing X.XXV to DAC pin line during shifts = GCU isn’t driving it.

Dash shows N but engine won’t crank → Gearbox dogs not fully cleared; sensor reads neutral, starter interlock disagrees. Wiggle the car / clutch + paddle tap. Not a starter fault.

Erratic shifting, no consistent pattern → Water in the GCU housing. Confirm the daily water check was actually happening. Document contamination before drying (warranty).

Compressor fuse blows immediately or after a short run → Relay diode, or water in the compressor head. Compressor is a four-event replacement item. Bulletin: 2025-09-12 Compressor TSB (includes Kleinn fuse replacement).

Compressor runs continuously, system tight → MOSFET stuck open on the GCU; documented track-side workaround redirects control to MOSFET 6 (procedure on the gcu-debugging page). Remember: compressor circuit is always hot via the ABS fuse — pull the fuse to stop it, not the ignition.

FALLBACK: Using safe default timing in the serial log → Pressure sensor (A6) wiring. Shifts still work at fixed timing; sensor stuck-high keeps the compressor off by design.

Electrical

Voltage droop when fans/loads kick on, recovers at revs or when load drops → Charging system path: regulator/rectifier, battery, main power connections. R/R and stator are Suzuki-side — maintenance/suzuki-service-manuals.md. Pages: maintenance/electronics-and-wiring/main-harness.md. Bulletin: 2025-06-23 Battery (+) Wire Relocation.

Single dead subsystem → Fuse → connector → harness segment. main-harness.md has the distribution map.

Suspension / chassis

Loose/rattling control arm interfaces → Bulletin 2025-11-03 Control-Arm Retaining Compound.

Worn/notchy spherical bearings → Bulletin 2025-11-04 Upgraded Spherical Bearing and Bearing Install Tools.

Rod-end misalignment binding at travel extremes → Bulletin 2026-01-16 Misalignment Spacer.

Fuel / fire system

Installation and sealing issues have dedicated bulletins: 2025-09-22 6 Gal Fuel Cell Installation, 2025-07-21 Sealing Washers (12 gal), 2025-07-02 Fuel and Fire System TSB, 2025-06-23 12 Gal Vent Line Relocation, 2025-09-17 Lifeline Fire Suppression. Any fuel smell, seep, or fire-system question → fetch the bulletin before improvising.