What it's for
The reverse switch function gives the ECU a single, reliable answer to "is the car in reverse?" Other features build on it, such as switching reverse lights or a reverse lockout. The signal usually comes from the gearbox's reverse light switch, or from the vehicle CAN bus on cars that already broadcast it.
Choosing the input mode
Reverse Switch Input Mode has two choices:
- Digital - Switched: a wired switch on any free AVI (analog voltage input) or SPI (synchronized pulsed input).
- Vehicle CAN: the ECU reads reverse from the car's own network, with no extra wiring.
Wired to an AVI
An AVI reads a voltage, so you tell it where "on" and "off" are. Set Switch On Voltage and Switch Off Voltage with a gap between them, so small fluctuations can't make the input chatter.
Example: a switch that pulls the input to ground when reverse is selected. The input sits near 5V with the switch open and near 0V with it closed. An on voltage around 1V and an off voltage around 4V gives a wide, stable band between the two states.
Wired to an SPI
| Setting | What it does | Our advice |
|---|---|---|
| Edge Select | Falling if the switch grounds the input when active, Rising if it feeds voltage to it | Match how the switch is actually wired |
| Sensor Type | How the input interprets the signal | Hall Effect for a switch input |
| Pull Up | Holds the input high when nothing is driving it | On for a switch that only grounds the input |
| Arming Voltage (table) | The voltage the signal must pass before the ECU starts watching for an edge. Only shown when the SPI signal type is Reluctor | Rarely needed for a simple switch |
| Glitch Filter (table) | How long, in microseconds, the signal has to stay changed before it counts. Anything shorter is ignored | Increase it if the reading flickers from electrical noise |
Checking it
With the engine off, select reverse and watch the Reverse Switch channel in NSP. It should switch cleanly each time, without flickering. If it does flicker, check the ground at the switch first, then widen the AVI voltage gap or raise the SPI glitch filter.
More on how SPI filtering works is in glitch filter and arming voltage. Elite owners should see the Elite reverse switch article.
