GCU documentation and support
Apex Control Innovations is not HTG Electronics sp. z o.o. and is not affiliated with, endorsed by, or a successor to it. HTG Electronics ceased operating in 2024. The firmware running on GCU hardware was written by Adam Klama, who now maintains this documentation independently through Apex Control Innovations. HTG and HTG Tuning are trade marks of HTG Electronics sp. z o.o., referenced here only to identify the hardware described.
Last reviewed: 2026-08-06
If you own a GCU, this is where to start. Firmware updates, hardware repair and configuration help are all available, and the technical documentation your unit needs is on this site.
The GCU is a gearbox control unit — a standalone controller that drives an automatic or dual-clutch transmission directly. The hardware is still serviceable and the firmware is still maintained. Most of what you need is in the main documentation, which covers the current hardware and applies to your unit wherever the wiring and configuration are the same.
Start here
| If you want to | Go to |
|---|---|
| Know whether anyone can still help you | Support status |
| Get a unit repaired, reflashed or tested | Repair and service |
| Find a wiring diagram or pinout | Wiring and pinouts |
| Update firmware, or find the configuration software | Firmware and software |
| Work out which unit you have | Identify your unit |
| Diagnose a fault code or a symptom | Faults and diagnostics |
| Compare your options for a new build | Continuing with current hardware |
Before you ask for help
Three pieces of information turn a slow conversation into a fast one: the serial number stamped on the unit, the firmware version it is running, and the transmission it is driving. Identify your unit explains where to find each.
Evaluating hardware for a new build rather than running an existing unit? See Which device do I need?