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

Battery voltage reading in the 11.4–13.6 V range, with a sag of up to ~1.5 V while the rear radiator fans run → This is NORMAL. Do not route it to the charging-system tree. Normal operating range is ~11.4–13.6 V. Expect a sag of up to ~1.5 V while the rear radiator fans are on; larger on an AGM battery, much smaller on lithium (which also runs slightly higher voltage). A reading in this range is not a fault, does not need a voltage-drop test, and does not implicate the regulator/rectifier, battery, or main power connections. Diagnose only when voltage stays below the normal range under no load, or sags far beyond ~1.5 V with fans/loads. The dash has no documented voltage alarm threshold — do not invent one.

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.

Throttle unresponsive / car feels like it ran dry / tank reads nearly full after a long stint (6-gal cell) → Stuck fuel flapper inside the 6-gallon tank. A stuck flapper blocks fuel flow and can starve the engine while fuel is still in the tank, and it makes the tank read fuller than it is. Check the flapper before replacing the pump. Page: maintenance/each-weekend/checking-fuel-pressure.md — configure the fuel pressure channel on the AiM dash so pressure is visible; starvation shows up as pressure dropping before the car feels out of fuel. Cross-check the fuel level sender: it is not precise for quantity but should flag a 0-fuel condition; the owner tracks its full/empty readings. Still showing fuel while the car acts dry points at a delivery fault, not an empty tank.