Torque Unlock — removing torque limits in the ECU and gearbox

Torque Unlock removes torque limits in the software of both the transmission control unit (TCU) and the engine ECU. After Stage 1 or Stage 2 the engine can make more torque, but limits set for the stock driveline cut the gain off before it reaches the wheels. For tuners: send us the original file and get a ready-to-flash file with corrected checksums, on average in 30–60 minutes.

Who limits torque: the gearbox and the ECU itself

The engine ECU and the TCU exchange data over CAN all the time. The ECU tells the gearbox the actual engine torque. There is no torque sensor on the engine: the ECU calculates the figure from fuelling, boost and ignition timing. The TCU uses that number to set clutch pressure and decide when to shift.

Requests go the other way too. During a shift the TCU asks for a brief torque cut so the gear engages smoothly and with less wear. It also sends a standing limit: do not give the engine more than this. The ECU collects every request (the pedal, its own limiters, the gearbox limit) and obeys the lowest one.

Torque limits inside the engine ECU

Some limits live in the engine ECU and need no request from the gearbox. A manual car has no TCU at all, so all of the driveline protection sits in the engine file.

• Per-gear limits. The allowed torque can depend on the engaged gear. In a low gear the torque at the wheels is several times higher than in top gear, because the gear ratio multiplies it. Hence separate caps for the low gears: on the Toyota Tacoma, according to tuners, the stock calibration held a load ceiling in 1st gear even where boost was higher in the other gears.
• Gearbox protection. BMW ECU logs have a separate state, GS_AUTARK, for self-sufficient gearbox protection: the ECU limits torque on its own, without waiting for a request from the TCU.
• Clutch protection on manual cars. The ECU watches clutch slip and cuts torque if the clutch is overloaded. BMW has a separate torque limitation state for it, and an FCA patent describes the whole logic: the unit calculates the energy going into a slipping clutch and trims the torque request as it nears a damage threshold.

All these limits are set for stock torque. After a Stage tune they cut the gain in particular gears just like the gearbox limit does.

Why a tuned car hits a torque plateau

A stock engine often runs close to the driveline limits. An example from calibrators' practice: a BMW 335i F30 makes 450 Nm from the factory, and the ZF 8HP45 limiter sits at about 465 Nm. Stage 2 adds roughly 150 Nm to this engine, yet a stock TCU still holds it at 465. Instead of the new torque curve you get a flat plateau.

TCU limits usually differ by gear. On the ZF 8HP the lowest ones are typically in 3rd and 6th, hence the classic complaint: the car pulls in some gears and goes flat in others. On a DQ250 DSG the stock calibration caps torque at roughly 350–380 Nm.

There may be no fault codes at all: the driveline is healthy and simply follows its calibration. Logs show the cause. Actual torque flattens at the same value while the request is higher. On a BMW the torque limitation state also tells you the source: the GS_PERM bit means a limit sent by the transmission, GS_AUTARK means gearbox protection inside the ECU.

Why not hide the extra torque in the engine file

A common workaround is to make the ECU report less torque than the engine really makes, so the gearbox stays out of the way. The car drives, but the TCU now calculates pressures from the understated figure. In the same 335i example the engine makes 600 Nm while the gearbox is told about 450. The TCU knows nothing about the other 150 Nm and applies pressure meant for 450. Shifts get soft and slow first, then the clutches wear from slipping on every shift and while driving in gear.

The right order is the opposite: the ECU reports real torque, and the limit is raised in the gearbox itself. If torque has gone up a lot, the pressures are adjusted along with the limit. That is the Oil Pressure Optimizations option.

What changes in the files

Checksums are recalculated, so the file is ready to flash straight away. If the engine is still stock, start with the engine file: Stage 1 or Stage 2. On a stock engine Torque Unlock gives nothing, because torque is already below the limit.

Clutches and service life: what to know before flashing

A limit in the file is software. The hardware stays the same: the same clutches, friction plates and shafts. Every extra newton-metre adds load and heat whenever the clutch slips or the car pulls away hard. COBB's findings, quoted in the ECUTEK knowledge base, put the risk of early clutch failure on the DQ250 at measured torque above roughly 520 Nm.

So raise the limits to match the real engine torque, not to the maximum. On a manual car the stock clutch has to hold the torque: if it already slips on a stock engine, it is too early to remove limits. Before flashing:

• check the gearbox fluid level and condition: with low fluid, slip and overheating come sooner;
• read the TCU fault memory and make sure the gearbox is healthy, since software will not fix worn clutches or faulty hydraulics;
• after flashing, reset the adaptations and let the gearbox relearn. On a DSG this step is mandatory, otherwise the unit does not apply the new parameters.

Which units are covered

The list further down this page covers gearbox units: ZF torque-converter automatics (8HP of several generations, 9HP, 6HP), DSG DQ200, DQ250, DQ38x, DQ400E and DQ500, S tronic DL382 and DL501, VGS units (NAG2, NAG3, FDCT) and a few other families. Limits in the engine ECU are removed in the engine file: send it together with the gearbox file or on its own. If your unit is not in the list, send the file with a request and we will check whether there is a solution.

How to order the file

1. Read the original files of the TCU and the engine ECU via OBD or on the bench with the tool you use. We need unmodified stock files.
2. Upload them to the portal and select TORQUE UNLOCK. For a big torque increase, add OIL PRESSURE OPTIMIZATIONS. Say in the comment which Stage the engine is on and what gearbox the car has: automatic, dual-clutch or manual.
3. Get the finished file with recalculated checksums, on average within 30–60 minutes.
4. Flash the files, reset the gearbox adaptations and check in the logs that torque no longer flattens out.