Continuing with current hardware

Keeping a working GCU is a reasonable decision. It is serviceable, its firmware is maintained, and nothing on this page is an argument against it. If your car works, the useful pages are Repair and service and Faults and diagnostics.

Two things to know before you decide to keep one, neither of them a reason not to: units in some serial ranges have known service items associated with them, and a hardware revision boundary decides which firmware a given unit can run — Identify your unit places yours.

This page is for the other case: a new build, a different transmission, or a unit that is not worth repairing.

Two architectures, not one product

Current hardware splits the job two ways. The GCU does the first of them.

The standalone transmission controller replaces the factory transmission control unit and drives the transmission directly — solenoids, sensors, speed signals. You control shift points and pressures. This is the same architecture as the GCU, so it is the closer relative.

The IOcan gateway keeps the factory transmission control unit in place and recreates the vehicle environment it expects. The factory unit keeps doing the control; the gateway makes it believe it is in its original car.

Which device do I need? walks through the decision. 8HP controller comparison compares both against running the transmission from the engine control unit.

What carries over

  • The wiring approach. Solenoid, sensor and speed-signal circuits are the same problem, and the standalone wiring diagrams will look familiar.
  • The concepts. Inputs, outputs, controllers and maps are the same model.
  • Your transmission knowledge. Adaptations, torque calibration and shift behaviour transfer directly.

What does not

  • The configuration. The 1.x configuration format does not transfer. Configuration is rebuilt, not migrated — the same as crossing the 1.1 boundary within the legacy line.
  • The harness, exactly. Pin functions differ. Read Controller pinout against your existing harness before assuming a swap.

What a gateway gives up

If you are considering the gateway rather than the standalone controller, this is the honest part, and it is a real constraint rather than a small one:

  • Shift points, drive modes and torque converter lockup live in the factory transmission unit's own tune. There is no device parameter for any of them.
  • Shift firmness is not a parameter either. You influence it indirectly, through an accurate torque signal.
  • The engine control unit performs the torque cut, not the gateway. If it ignores the request, shift quality suffers.

If direct control over shift points and pressures is why you chose a GCU, the standalone controller is the equivalent, not the gateway.

Read the limitations first

Stated limitations lists what the current devices do not do — platform maturity, transmissions being withdrawn, and configuration fields that are visible but inert. Read it before deciding. It is the page that will tell you if the answer is "keep what you have".

Planning a build and want the hardware question settled? See Which device do I need?