What the table does
When NSP's Transmission Control function is holding a gear (not mid-shift), In Gear Base Duty is the duty cycle sent to the line pressure control solenoid. How it's used depends on your control mode:
- Open loop: the table value is exactly what the solenoid gets.
- Closed loop: the ECU adds a PID correction on top of the table value. The better the table, the less the PID has to fix.
During shifts a separate table takes over; see Shifting Base Duty Cycle. For the big picture, start with line pressure control.
Why more duty usually means less pressure
Transmissions are designed to fail safe. If a wire breaks or a connector falls off, the car should still drive rather than slip itself to death. So most line pressure solenoids give full line pressure at zero current, and pressure drops as current goes up. That's backwards from what many people expect, so keep it in mind: a higher duty number is asking for lower pressure.
Choosing the axes
| Control mode | Axis 1 | Axis 2 | Why |
|---|---|---|---|
| Open loop | A torque proxy: Load (Normalised Air Mass Flow), Manifold Pressure, Engine Demand or Throttle Position | Gear | You're tuning duty directly, so it needs to follow how hard the engine is pushing |
| Open loop w/ Target, or Closed loop | Line Pressure Control Target Pressure | Transmission Oil Temperature | The table becomes a translation from wanted pressure to duty, and solenoid resistance changes a lot with temperature |
Battery voltage could stand in for oil temperature on that second axis, but once the engine is running it barely moves, so temperature is the more useful choice. Set this table up before you start tuning targets. If it's wrong, every target you tune later is built on sand.
Filling it in: three methods
If a base map exists for your transmission, import its line pressure control settings and skip most of this. Otherwise, pick the best method you have the equipment for.
1. With a line pressure sensor (best)
This is the quickest and most accurate. You'll need a line pressure sensor fitted, enabled and calibrated. Then for each target pressure cell, adjust duty until the Line Pressure channel reads that value. Work from the highest pressure (lowest duty) upward.
The engine must be running because the transmission pump makes the pressure. If idle can't build enough, hold the engine at a steady cruise RPM while you work.
2. With a multimeter measuring current (good)
Many workshop manuals include a table of solenoid current versus line pressure. If yours does, you can do this with the engine off:
- Use those pressures as your target axis. Where the manual gives a range, use the midpoint.
- Put the meter in series with the solenoid. The simplest way is to de-pin that ECU terminal, connect it to one meter lead, and use a temporary wire and pin in the ECU connector to the other lead.
- Starting at the highest pressure (lowest current), raise duty until the meter shows the current the manual calls for, then move to the next cell.
Manufacturing tolerances mean this won't be perfect, but it's plenty to tune from. A pressure sensor is the upgrade if you want more precision.
3. Calculating it (rough, but workable)
No sensor and no meter? You can estimate duty with Ohm's law, then tune around it.
- Get the solenoid's resistance, ideally measured at the fluid temperature you'll tune at (typical operating temperature is about 212°F / 100°C). If you can't measure it, use the middle of the manual's spec.
- For each cell, find the current the manual gives for that pressure, then voltage needed = current x resistance.
- Duty = 100% x needed voltage / supply voltage. Take supply voltage from the Battery Voltage channel with the engine running, ideally at cruise.
Example with made-up numbers: a solenoid measuring 5 ohms that needs 1.0 A for a given pressure needs 5.0 V effective. With 14.0 V at the battery, that's 100 x 5.0 / 14.0, or about 36% duty.
If you only fill in the hot-oil column, the transmission will behave differently when cold because the solenoid's resistance is lower. Fill in cold columns too, even roughly, and use temperature correction where it helps.
Troubleshooting
| Symptom | Usually |
|---|---|
| Measured pressure far from target in closed loop | Base duty is off, so the PID is doing too much of the work |
| Slipping in gear | Duty too high for that cell (remember, more duty means less pressure) or target too low |
| Fine hot, harsh or slippy cold | Only the hot temperature column has been set up |
| Pressure can't be built during setup | Engine at idle isn't spinning the pump fast enough; hold a cruise RPM |
FAQ
Do I need a line pressure sensor?
No, but it's the easiest and most accurate way to build this table, and it makes closed loop possible.
Where do I set the target pressure?
In the In Gear Target table. This table only converts that target into solenoid duty.
Building an auto conversion? Book a free consultation and we'll help you plan it.
