GCU
The Gear Control Unit (GCU) sits between your paddles and the gearbox. It reads your paddle inputs, fires the air valves that move the shift drum, keeps the compressor topped up, and — on current cars — keeps an eye on the engine and refuses shifts that would over-rev.
Every Rush SR has a GCU. Which one you have depends on when your car was built.
Active GCU vs Legacy GCU
Section titled “Active GCU vs Legacy GCU”| Active GCU | Legacy GCU | |
|---|---|---|
| Fitted to | Newer builds (Gen2, drive-by-wire) | Earlier builds (Gen1, throttle cable) |
| Brain | 32-bit, 120 MHz, 192 KB RAM | 8-bit, 16 MHz, 8 KB RAM |
| ECU link | Native CAN — reads RPM, gear, and throttle position live | None — blind voltage output |
| Shift validation | Closed loop off the gear sensor — confirms in under 10 ms, auto-retries a missed shift | Open loop, timed |
| Money-shift protection | Projects the resulting RPM and refuses the shift | None |
| Logging | 2 MB flash, per-session logs, GPS wall-clock timestamps, crash log, reset cause | None |
| Tuning | 40 live tunables via the flasher, never locked | 2 EEPROM values, locked once the car has shifted |
| New to this unit | Auto-downshift, brake-light control, wheel-speed emulation, dash telemetry, watchdog + safe mode, car/moto modes, progressive neutral finder | — |
Which GCU Is in My Car?
Section titled “Which GCU Is in My Car?”Not sure which you have? It’s easy to tell at a glance.
- Active GCU — a small flat black box with a single plastic harness connector, about the size of two decks of cards. One multicolor status LED. It flashes with
.binfiles. - Legacy GCU — a much larger grey rectangular box with two metal connectors, roughly the size of a large coffee can. Separate red/yellow/green diagnostic LEDs. It flashes with
.hexfiles.
Still not sure? Connect the GCU Flasher and read the version — the Active GCU reports firmware 5.x, the Legacy GCU reports 3.x.
Choose Your Page
Section titled “Choose Your Page”- Have the Active GCU? See GCU — Active for flashing, live telemetry, log pulling, and troubleshooting.
- Have the Legacy GCU? See GCU — Legacy for firmware and flashing.
- Having mechanical shift trouble — missed shifts, false neutrals, compressor faults? The Shift Debugging page applies to every car, regardless of GCU generation.