What this table controls
When the Nexus transmission controller is changing gears, the Shifting Base Duty table sets the duty cycle sent to the line pressure control solenoid. There's a separate In Gear Base Duty table for when the transmission is holding a gear. How the ECU uses this table depends on your control mode:
- Open loop: the value in the table is exactly what the solenoid gets.
- Closed loop: the table gives the starting point, and the PID controller adds or subtracts from it to hit the shifting target pressure.
Why more duty usually means less pressure
Transmissions are designed to fail safe. If the solenoid loses power or a wire breaks, you still want the car to drive, so most line pressure solenoids give maximum line pressure with no current flowing. Adding current reduces pressure. That's backwards compared to most things you tune, so keep it in mind: in this table, a higher duty cycle normally means softer, lower-pressure shifts.
Choosing the axes
| Control mode | Axis 1 | Axis 2 |
|---|---|---|
| Open loop | Something that tracks engine torque: Normalised Air Mass Flow, manifold pressure, Engine Demand or throttle position | Transmission Control Current Shift |
| Open loop with target, or closed loop | Line Pressure Control Target Pressure | Transmission Oil Temperature |
In the target-based modes, oil temperature is the second axis because the solenoid's coil resistance changes a lot with temperature. The same duty gives a different current, and so a different pressure, hot versus cold. Battery voltage would also work as an axis, but once the engine is running it barely moves, so temperature is the more useful choice. Set up the axes before you start tuning values.
Filling in the table
If there's a Haltech base map for your transmission, import its line pressure settings and start from there. If there isn't, there are three ways to build the table, from most to least accurate.
1. With a line pressure sensor (best)
If you have a line pressure sensor fitted and calibrated, this is quick and accurate. With the engine running so the pump makes pressure, adjust the duty in each cell until the Line Pressure channel reads the pressure you want. Start at the high-pressure, low-duty end and work up. If idle doesn't make enough pressure, hold the engine at a steady cruise rpm while you work.
2. With a multimeter measuring current
This works with the engine off, but you need the solenoid's current-to-pressure chart. That's often in the factory workshop manual for the transmission. Build the target pressure axis from the pressures in the chart. Where the manual gives a pressure range for a current, use the midpoint. Manufacturing tolerances mean it won't be perfect, but it's close enough to tune from.
To measure current, the meter has to be in series with the solenoid. The easiest way is to de-pin the solenoid's wire from the ECU connector and connect it to the meter's red probe, then fit a temporary wire with a terminal into the empty ECU position and connect that to the black probe. Starting at the lowest-current cell (usually the highest pressure), raise the duty until the meter reads the current from the chart. Need a sketch of this hookup? Ask us and we'll send one over with advice for your build.
3. By calculation (a rough start)
The least accurate method, but fine as a starting point, since you'll refine it anyway.
- Measure the solenoid resistance at the fluid temperature you're tuning for. If you only tune one temperature, make it normal operating temperature, around 212 °F (100 °C), and accept that cold shifts won't be ideal. If you can't measure it, use the midpoint of the resistance range from the workshop manual.
- For each cell, multiply the current you need by the resistance (Ohm's law, V = I × R) to get the average voltage the solenoid needs.
- Divide that by the running battery voltage from the Battery Voltage channel, ideally at cruise, and multiply by 100 to get duty.
As an illustration with made-up numbers: a coil you measured at 6 ohms that needs 0.8 A needs 4.8 V. With 14.0 V at the battery, that's 4.8 / 14.0 × 100, or about 34% duty.
Troubleshooting
| Symptom | Usually |
|---|---|
| Shifts get harsher as you add duty | This solenoid works the normal way round (more current, more pressure). Check the manual |
| Shifts feel different hot versus cold | Only one temperature row tuned. Add rows for cold fluid, or use temperature correction |
| Closed loop hunts during shifts | Base duty too far from reality, so PID is doing all the work. Tune the base table closer |
| No change in pressure at all | Check the line pressure control wiring and output setup |
For the bigger picture, see line pressure control.
