What the function does
When a Nexus ECU is running transmission control, Paddle Shift Inputs is how the driver requests a gear. Don't let the name narrow your thinking. Any up and down request switch works, including the tiptronic-style plus/minus gate on an automatic's shifter.
A request only turns into a shift when the transmission function is in a mode that accepts manual requests and nothing is blocking the change. If something is blocking it, the request isn't thrown away. It's queued.
The paddle shift stack
The queue is a channel called the Transmission Control Paddle Shift Stack. It counts shifts the driver has asked for that haven't happened yet, in either direction.
Here's why it's useful on track. You're in 6th, braking for a hairpin you take in 2nd. Tap down four times, even before you're on the brakes, and focus on your braking point. The ECU works through the four downshifts as each becomes safe. You don't have to time each click against engine speed.
The stack respects the gearbox. It never queues beyond top gear or below first, so tapping down ten times in 3rd just gets you to 1st. (Getting into Neutral and Reverse works differently, covered below.)
What holds a shift on the stack
- The Shift Inhibit table conditions aren't met.
- Block Down Shift Over-Rev is on, and the downshift would push Engine RPM past the Main RPM Limiter End RPM.
- Another shift is still happening.
- The post-shift block-out period hasn't expired.
What clears it
- The queued shifts are completed.
- A shift happens in the opposite direction.
- The driver pulls the opposite paddle. That wipes the queue and replaces it with a single request in the new direction.
That last rule is a nice safety valve. If you queue three downshifts and then realize you've overdone it, one tap of the upshift paddle cancels them.
Shifting to Neutral and Reverse with the paddles
Paddles Shift to Neutral lets the driver select Neutral and Reverse from the paddles, so you don't need a separate gear selector position input. That's ideal for a race car with a sequential box and no PRNDL lever.
It only works if the ECU can actually command the transmission into Neutral or Reverse. Many sequential gearboxes and some modern automatics can do this; older automatics generally can't. NSP shows the enable setting in red if you turn it on with a transmission type that doesn't support it. With Generic Automatic selected, it's your call whether the transmission is capable. The ECU does one sanity check: the solenoid output pattern for Reverse has to be unique, because on some boxes the physical shifter is what separates reverse from the forward gears.
If your gearbox has a mechanical lock-out on Neutral or Reverse, the ECU can't shift past it. Either remove it, hold it disengaged with something solid, or make releasing it part of the driver's routine. Leaving it in place and asking the ECU to shift into it can cause unexpected behavior and damage.
Getting into Neutral
- Be in first gear (Gear channel = 1) or in Reverse (Gear channel = -1).
- If vehicle speed is set up, and we strongly suggest it is, the car must be at or below Paddles Shift to Neutral Maximum Speed. The suggested range is 0-10 mph (0-15 km/h).
- Hold the downshift paddle (from first) or upshift paddle (from Reverse) for at least the Paddles Shift to Neutral/Reverse Hold Time. The suggested value is 300 ms. A deliberate hold is what stops a clumsy click from dropping you into Neutral mid-corner.
- Keep the clutch and/or brake applied until you have real confirmation you're in Neutral, from a neutral light or a gear display fed by a gear position sensor.
That confirmation matters most with motorcycle-style gearboxes, where Neutral sits halfway between 1st and 2nd and it's easy to miss it on either side.
From Neutral, one tap of the upshift paddle selects first. On a clutched transmission, have the clutch in before leaving Neutral.
Getting into Reverse
- Be in Neutral (Gear channel = N / 0).
- If vehicle speed is configured, the car must be stopped (speed channel reads 0).
- Hold the downshift paddle for the same hold time.
- On a clutched gearbox, keep the clutch in while it shifts.
Calibrating the paddles
The paddles are read as voltages on one sensor input, so the ECU needs to know what "up" and "down" look like.
| Setting | What it does | Our advice |
|---|---|---|
| Upshift Request Voltage | The voltage seen when the upshift paddle is pressed | Hold the upshift paddle and press Calibrate rather than typing a number |
| Downshift Request Voltage | The voltage seen when the downshift paddle is pressed | Same process with the downshift paddle held |
| Voltage Tolerance | How far either side of each request voltage still counts as a press | Wide enough to cover noise and temperature drift, narrow enough that the two windows never overlap and neither window includes the released voltage |
| Paddles Shift to Neutral Maximum Speed | Highest road speed at which Neutral can be selected | 0-10 mph (0-15 km/h) |
| Paddles Shift to Neutral/Reverse Hold Time | How long a paddle must be held to select Neutral or Reverse | 300 ms, then adjust to driver preference |
After calibrating, log the input and click each paddle a few dozen times. Watch the voltage when released too; if the released voltage wanders toward either window, fix the wiring before you trust it. Wiring details are in Paddle Shift Wiring.
Troubleshooting
| Symptom | Usually |
|---|---|
| Paddle press does nothing | Transmission not in a mode that accepts paddle requests, or voltage outside the tolerance window |
| Downshift happens late, or not at all | Block Down Shift Over-Rev is protecting the engine; the shift waits on the stack until RPM allows it |
| Random or double shifts | Tolerance too wide or a noisy signal; recalibrate and check grounds |
| Unexpected shift after a delay | A queued request on the stack finally became possible |
| Can't select Neutral | Not in 1st or Reverse, too fast, paddle not held long enough, or enable shown in red |
| Neutral overshoots into 2nd | Normal risk on motorcycle-type boxes; keep the clutch in and confirm on the gear display |
FAQ
Can I use my factory shifter's +/- gate instead of paddles?
Yes. The function doesn't care what the switch looks like, only what voltages it produces.
Why didn't my downshift happen when I pulled the paddle?
Most often because the shift would have over-revved the engine. It stays queued and happens once speed drops enough, which is exactly what you want going into a slow corner.
Do I need a gear position sensor?
Not strictly, but the driver needs a trustworthy way to confirm Neutral before letting go of the clutch or brake: either a neutral light or a gear display driven by a gear position sensor. Related features worth reading about are Flat Shift and Ignition Retard.
