Why gear detection matters
A gear channel is one of the most useful axes in a tune. We use it for boost by gear, ignition trims by gear, per-gear launch and traction settings, shift lights and dash displays. If the gear reading is wrong, all of those follow it, so it pays to choose a method that suits your hardware.
Choosing a Gear Detection Type
| Type | How it works | Best for |
|---|---|---|
| Gear Ratio | Compares engine speed with road or shaft speed and matches the result to your configured ratios | Most manual cars with a vehicle speed sensor. Needs the Gear Ratios function set up |
| Gear Switch | A switch on the shifter, such as a load cell, counts up one gear per shift. A clutch press resets the count to zero | Sequential and dog boxes. See Gear Switch |
| Gear Position Sensor | A gearbox sensor that gives a different resistance in each gear | Transmissions fitted with one. It's the only option when the Transmission Type is Automatic |
| RPM Drop | Counts upshifts from the fall in engine RPM | Drag cars with only an engine RPM signal that never downshift. See RPM Drop |
| Use Selector Position | Gear comes from the selector ("PRNDL") input | Needs a Selector Position Type set, see below |
| CAN Input | Reads a gear value the vehicle broadcasts on CAN | Modern cars where the factory TCU or ECU already knows the gear |
| Transmission Control Function | Takes gear from the ECU's own transmission control, where you pick the gearbox (GM 4L60E/4L80E, Ford 4R70W and others) | Cars where the Nexus is also shifting the automatic |
Because it only counts RPM falls, it has no way of knowing about a downshift. That's fine on a drag car, but on a road course it will lose track of the gear within a lap.
Selector position (PRNDL / T-bar)
The Selector Position tells the ECU where the shift lever is, which on an automatic isn't always the same as the gear the transmission is in. The options are:
- Disabled: no selector signal.
- Voltage Input: a sensor with voltage-based calibration data, on an analog voltage input (AVI).
- CAN Input: the selector position comes from vehicle CAN.
- GM 4L60E / 4L80E: pick it when that's the transmission and the selector type you're using.
- One Input Per Position: a separate wire for each position (Park, Reverse, Neutral and each drive gear).
Older transmissions with a switch-based selector sometimes need converting. For example, the PRNDL signal converter for the Toyota A340 turns that transmission's signals into something the ECU can read.
Connections
| Input | Shows up when | Notes |
|---|---|---|
| Gear Switch Input | Gear Switch is the detection type | AVI or SPI. The clutch switch function must also be set up and wired, since it resets the count. Enter Switch On and Switch Off voltages that match your switch |
| Gear Voltage Input | Gear Position is the detection type | AVI or SPI |
| Selector Position Input | Voltage Input is the selector type | AVI or SPI |
When setting switch voltages, leave a clear gap between the On and Off thresholds so noise can't make the input toggle. A gear switch that double-counts is one of the most common problems we see.
Troubleshooting
| Symptom | Usually |
|---|---|
| Gear shows 0 or flickers at low speed | Gear Ratio method with no reliable speed signal at low speed. Normal when rolling slowly or with the clutch in |
| Gear count jumps two at once | Gear switch thresholds too close together, or switch bounce |
| Gear count never resets | Clutch switch not configured or not wired |
| Wrong gear on an automatic | Gear taken from the selector position, which shows where the lever is rather than the gear engaged. Recheck the Gear Detection Type against your Transmission Type setting (only Gear Position Sensor works with Automatic) |
See also Gear Position and Vehicle Speed.
FAQ
Which method is most reliable on a street car?
For a manual, Gear Ratio with a good speed sensor. For a modern car, CAN is hard to beat if the factory network already reports gear.
Can I use gear as a tuning axis straight away?
Yes, once the gear channel reads correctly. Confirm it in a log first, including through shifts and at a stop.
