What the Start Stop Button function does
On a Nexus ECU, the start button isn't just wired to the starter. The ECU reads the button and decides what to do with it: crank the engine, shut it down, or ignore a press that would be unsafe. That's why the settings are split into three groups: the button type, how it behaves in normal use, and what counts as an emergency stop. The cranking itself is governed by the starter motor settings, and the physical wiring is covered in start stop button wiring.
Button type
- Momentary: a spring-return push button that's only on while you're pressing it. The usual choice for a push-button start.
- On / Off Switch: the input stays on while the engine runs. This is the mode for a traditional key, where the key sits in run after starting.
- CAN Input: the button state arrives over CAN, for example from a keypad.
Normal starting and stopping
| Setting | Options | Our advice |
|---|---|---|
| Engine Start Press Type | Short / Single Press: one tap and the ECU keeps trying until the starter's maximum starting attempt time runs out. Hold Until Started: the ECU only cranks while the button (or key) is held in start | Single press feels like a modern car. Hold until started gives the driver more control on a race car or a hard starter |
| Engine Stop Press Type | Short / Single Press, or Long Press | Long press is harder to trigger by accident |
| Short / Single Press Stop Maximum Speed | 5.0 to 40.0. Above this speed a single tap won't stop the engine | Keep it low. It needs a working vehicle speed signal |
That speed lockout is the key safety feature. Above the set speed, an accidental bump of the button does nothing, but the driver can still kill the engine deliberately with a long press or a burst of panic presses.
Emergency stop settings
A long press, or several quick presses inside one second, tells the ECU to stop the engine whatever the conditions. Two settings define those:
- Minimum Hold Button: how long, in seconds, the button must be held to count as a long press. Range 0.5 to 2.0.
- Minimum Number of Button Panic: how many presses within one second count as a panic stop. Range 3 to 5. The floor of 3 exists so a double tap can't shut the engine off by mistake.
With the car safely stationary, try every way of stopping the engine: a short press, a long press and a panic burst. Everyone who drives the car should know how the emergency stop works.
Need help wiring a push-button start into your build? Contact us.
