What it measures and why it's useful
The transmission input RPM function reads the speed of whatever drives the gearbox input: the clutch on a manual car or the torque converter turbine on an automatic. There are two big reasons to add it:
- Overspeed protection. Clutches, converters and the parts behind them have limits. The ECU can raise a warning in ESP when input speed passes the RPM you set.
- Slip detection. If engine RPM climbs while input RPM doesn't follow, the clutch or converter is slipping. Seeing both channels side by side in a log makes that obvious.
Setting it up in ESP
| Tab and setting | What it does | Our advice |
|---|---|---|
| Wiring: input | Chooses where the sensor is connected | Use an SPI or DPI (synchronized or digital pulsed input) |
| Wiring: Edge Select | Which edge of each pulse is counted | Falling, unless the sensor's documentation says otherwise |
| Wiring: Sensor Type | Digital Hall effect or reluctor | Match the sensor fitted. Not sure? Read Hall effect or reluctor |
| Wiring: Pull Up | Provides the voltage a Hall sensor switches to ground | Turn it on for Hall sensors that don't have a pullup in the sensor or the harness |
| Calibration: Number of Teeth | Pulses per revolution of the shaft being read | Count the teeth on the target wheel |
| Diagnostics: Operating Max | Sets DTC P1699 when input RPM goes above your limit | Disabled by default. Set it below what your clutch or converter is rated for |
With the engine protection function active, you can give P1699 a DTC severity level, so the ECU can act on the fault instead of just recording it.
Checking it works
On a manual with the clutch fully engaged, input RPM should match engine RPM. On an automatic with converter lockup engaged, it should also match closely. If it reads a steady fraction or multiple of engine RPM in those conditions, your tooth count is wrong. If it's noisy or drops out, look at the pullup, sensor gap and wire routing first.
FAQ
Where does the sensor usually go?
Many automatics already have an input or turbine speed sensor from the factory, and that's often the easiest option. On manual gearboxes it usually means reading a toothed part turning at input shaft speed. Tell us about your gearbox and we'll help you find a good target.
What about the output side?
Pair this with a driveshaft RPM sensor and you can see the whole driveline, from engine to clutch to tail-shaft. For shift-related logic, see gear detection.
