Glossary

Terms as they are used in this wiki. Where a term means something slightly different in a swap context than in a factory car, the swap meaning is given.

Electrical

KL30 · Constant battery positive, live whether or not the ignition is on. Written BAT+ in some places. What to connect it to differs by device. IOcan is designed to sit on KL30 through a fuse, because it manages its own sleep. The standalone transmission controller has no low-power sleep mode and must not — its KL30 goes through a time-delay-off relay instead, held about 60 seconds after the ignition drops: advisory.

KL15 · Switched ignition. Asserting it is what makes the device active on CAN and wakes the transmission. A missing KL15 wire looks exactly like a dead CAN bus, which is the single most common first-install symptom.

KL31 · Ground / chassis return.

KL50 · Starter control.

Terminal numbering · The KLxx scheme is a German automotive convention (Klemme, "terminal"). It appears throughout BMW and VAG documentation.

Transmissions

ZF 8HP · ZF's eight-speed torque-converter automatic, used across BMW, Audi, Chrysler, Jaguar Land Rover and others. Built in generations — Gen 1, Gen 2, Gen 3 — which differ electrically and are not interchangeable in configuration.

DCT · Dual-clutch transmission, the generic term.

DKG · Doppelkupplungsgetriebe — BMW's name for its dual-clutch transmissions. DKG and DCT mean the same kind of gearbox; DKG is simply the BMW badge. In this wiki DKG refers specifically to the BMW units.

GS7D36SG / GS7D70SG · The Getrag dual-clutch units used by BMW. The two differ in torque capacity, bellhousing and sensor arrangement.

PDK · Porsche Doppelkupplung, Porsche's dual-clutch transmission. The 7DT45 is the variant documented here.

DQ250 / DQ500 · VAG dual-clutch transmissions, supported by the standalone controller.

Mechatronics · The integrated valve body, solenoid pack, sensors and — in most ZF and BMW units — the transmission control unit itself, mounted inside the gearbox. When people say "the TCU is in the box", this is what they mean.

Valve body · The hydraulic control plate that routes pressure to the clutches and brakes.

Torque converter lockup · Mechanically clamping the torque converter so it stops slipping, for efficiency. Behind a gateway the factory TCU decides this; it is not a gateway parameter.

TCC slip · Torque converter clutch slip — the speed difference across the converter clutch.

Tailshaft speed · Transmission output-shaft speed. The gateway prefers the TCU's own measurement of this over an external vehicle-speed input, because it is what the transmission itself measures.

Control units

TCU / TCM · Transmission control unit / module. The factory computer that runs the gearbox. Keeping it is the whole point of the gateway architecture.

ECU / DME / DDE · Engine control unit. DME is BMW's petrol engine controller, DDE its diesel controller.

PCM · Powertrain control module — a combined engine and transmission controller, as on the GM LS E38.

GWS · Gangwahlschalter — BMW's electronic gear selector, the shift-by-wire joystick in F- and G-series cars. It reports selections over CAN rather than moving a cable.

Gateway · A device that keeps the OEM TCU and recreates the CAN environment it expects. Contrast with a standalone controller, which replaces the TCU and drives the transmission's solenoids directly.

Communication

CAN · Controller Area Network, the vehicle bus everything here runs on. A differential pair, terminated at both ends with 120 Ω, giving ~60 Ω measured across the pair with the power off.

PT-CAN / PT-CAN2 · BMW's powertrain CAN buses. Many 8HP installations need both.

Baud rate · Bus speed. One node at the wrong rate does not just stay silent — it actively destroys traffic for everyone by sending error frames.

Termination · The 120 Ω resistors at each physical end of the bus. Exactly two, no more. The device's termination is software-switchable.

Bus off · The state a CAN controller enters after accumulated transmit errors, in which it disconnects itself entirely. "It worked, then went silent" is usually this.

ACK · The acknowledgement bit every CAN frame needs from at least one other node. A lone device on a bus cannot successfully transmit — "my device doesn't transmit" is very often "nobody acknowledges".

ISO-TP · ISO 15765-2, the transport protocol that carries messages longer than eight bytes over CAN by splitting them into sequenced frames. The basis for diagnostics and flashing.

UDS · ISO 14229, Unified Diagnostic Services — the request/response protocol that runs on top of ISO-TP for reading fault codes, reading data and flashing.

DTC · Diagnostic trouble code — a fault code stored by a control unit.

CAN preset · A ready-made frame definition in the configuration software for a known device, so you do not have to map frames by hand.

DBC · The standard file format describing a CAN database — which signals live in which frames, and how they are scaled.

Control and calibration

Adaptation · Learned corrections a controller stores to compensate for wear and unit-to-unit variation, typically clutch fill pressures and times. Corrections learned against a wrong torque signal stay learned — reset adaptations after changing the torque method or its calibration.

Limp home · A protective mode in which the transmission locks into one gear or a restricted set. It is a decision the TCU has made, usually for a reason stored in its fault memory — not a defect in itself.

Cut · A brief reduction of engine torque during an upshift, so the driveline is unloaded while the next gear engages.

Blip · A brief raise of engine speed during a downshift, to match the lower gear and avoid driveline shock.

Torque intervention · The general term for a transmission asking the engine to change its torque. Requested as a percentage or a torque limit — never as an ignition angle. The engine ECU decides how to achieve it.

DBW · Drive-by-wire — an electronic throttle. The DBW Modifier is a standalone-driver feature that executes a cut by overriding the pedal signal; it is not available on the OEM gateways.

VE · Volumetric efficiency — how completely the engine fills its cylinders, used by the air-model torque estimate. The VE tables are all-or-nothing: VE is applied only when all three are present.

Speed-density / Alpha-N · Two ways of estimating airflow — from manifold pressure and RPM, or from throttle angle and RPM. The VE Blending map weights between them.

Dead time · The delay between commanding an injector and it actually flowing, which must be subtracted before pulse width becomes fuel mass.

Diff ratio · Final-drive ratio between transmission output and wheels. With wheel diameter, it converts shaft speed to road speed — get it wrong and shift scheduling is built on a wrong speed.