What speed sensors do on an Elite ECU
It's easy to think of vehicle speed as a logging channel and nothing more. In practice a lot of the Elite's strategies lean on it: fuel and ignition corrections, traction control, idle control, boost control and gear detection all use it. If the speed is wrong, all of those behave wrongly too.
The Elite can take up to five speed inputs: one drive train sensor (normally on the transmission output) plus one for each of the four wheels. Each can be wired straight to the ECU or received over CAN on vehicles where that's supported.
How many sensors do you need?
For speed display and most functions, one good sensor is enough. Traction control is different, because it works by comparing a driven wheel to an undriven one. The minimum for each drivetrain:
| Drivetrain | Minimum for traction control |
|---|---|
| Front wheel drive | One front wheel sensor (or the drive train sensor) plus at least one rear wheel sensor |
| Rear wheel drive | One rear wheel sensor (or the drive train sensor) plus at least one front wheel sensor |
| All wheel drive | At least two sensors, paired as a front wheel plus a rear wheel, a front wheel plus the drive train sensor, or a rear wheel plus the drive train sensor |
On a rear-drive car that means a transmission speed sensor alone won't give you traction control. You also need a front wheel sensor so the ECU knows how fast the car is actually traveling. Our guide to using ABS wheel speed sensors covers tapping into factory sensors.
Wiring tab
Options
- Main Source: the sensor the ECU treats as "vehicle speed" for every function that asks for it. On a rear-drive car we usually pick an undriven front wheel so wheelspin doesn't inflate the reading. The drive train sensor is a fine choice when it's the only one fitted.
- Drive Train Sensor, Front Left Wheel, Front Right Wheel, Rear Left Wheel, Right Rear Wheel: enable only the sensors you actually have, and for each one choose whether it arrives wired or over CAN.
Connections
For each wired sensor, choose Digital Frequency and assign an input. Use an SPI (Synchronised Pulsed Input), since these are the inputs built for pulse-train signals like speed. Then set:
| Setting | What it does | Our advice |
|---|---|---|
| Edge Select | Which edge of each pulse the ECU counts | Falling, unless the sensor maker specifies otherwise |
| Sensor Type | Digital Hall effect or reluctor | Match the physical sensor. A two-wire sensor is usually a reluctor; three wires usually means Hall. See Hall effect or reluctor? |
| Pull Up | Enables the internal pull-up resistor | Turn it on for Hall sensors that need one and don't have it built into the sensor or harness |
A Hall sensor with no pull-up usually reads zero or produces an erratic signal, so if speed never shows up on a Hall sensor, check this setting first.
Calibration tab
Calibration teaches the ECU how many pulses equal a unit of distance. It differs slightly between wired and CAN inputs.
Wired sensors
- Enter a Calibration Speed, the speed you'll hold during calibration.
- Drive the car at exactly that speed, confirmed with a GPS source rather than the factory speedometer, which usually reads high.
- Press Calibrate for each enabled sensor. The ECU measures and stores pulses per kilometer or pulses per mile for each.
If you already know the pulses per mile, for example from the sensor's tooth count and your tire size, you can type it in directly instead.
CAN sensors
The same process, but instead of counting pulses the ECU calculates a percentage correction for each speed arriving over CAN. That's how you account for a change in tire rolling diameter from the factory size.
Calibrate with a passenger and a GPS app, on a flat, straight road, at a steady speed like 40 or 50 mph. Holding steady matters more than which speed you choose. Recalibrate any time you change tire size or final drive ratio.
Driveshaft RPM sensor
These settings only appear once the drive train sensor is enabled on the wiring tab.
- Number of Teeth: pulses per driveshaft revolution, equal to the number of magnets in a driveshaft collar. Typically 2, 8 or 12. Haltech's driveshaft split collars are 8-magnet designs.
- Max Derivative: the fastest believable rate of change for driveshaft rpm. Anything quicker is treated as noise and filtered out.
- Warning Maximum: above this driveshaft rpm, related items in ESP flash red as a warning.
More detail is in our driveshaft RPM sensor article.
Diagnostics tab
The Elite can flag a failed or disagreeing sensor with a trouble code. How it decides depends on how many sensors you have.
With one or two sensors, a sensor is suspect if it reads zero speed while all of these hold for more than 10 seconds: throttle below the User Demand Minimum, MAP below -60 kPa (engine under strong vacuum, as on a closed-throttle overrun), and rpm between 2000 and 5000. In plain English: the engine is being driven by the wheels, so the car must be moving, yet the sensor says it isn't.
With more than two sensors, the ECU compares each one to the average of all of them. If rpm is below 4000, throttle is under 20%, and one sensor is more than 15 km/h (about 9 mph) away from the average, it's flagged.
| Diagnostic | Code set |
|---|---|
| Drive Train Speed | P0500 |
| Front Left Wheel Speed | C1024 |
| Front Right Wheel Speed | C1022 |
| Rear Left Wheel Speed | C1028 |
| Rear Right Wheel Speed | C1026 |
| Average Wheel Speed | C1029 |
Enable only the diagnostics for sensors you have fitted. A diagnostic enabled for a sensor that isn't there is just a guaranteed fault code.
Troubleshooting
| Symptom | Usually |
|---|---|
| Speed always reads zero | Wrong input selected, sensor type set incorrectly, Hall sensor missing its pull-up, or no power/ground to the sensor |
| Speed jumps or spikes | Noisy signal, unshielded wiring near ignition, or the wrong edge |
| Speed reads consistently high or low | Calibration done against the factory speedometer, or the tire size has changed |
| Traction control won't work | Missing the required sensor pairing for your drivetrain (see the table above), or one of those sensors not enabled or calibrated |
| P0500 or C-codes on a healthy sensor | Diagnostic enabled for a sensor that isn't fitted, or a sensor calibrated at a different speed from the others |
Vehicle speed sensor FAQ
Can I use my factory ABS sensors with an Elite ECU?
Often, yes. Either wire them to spare SPI inputs, or on supported vehicles receive wheel speeds over CAN. Check whether the ABS module needs the signal as well before you splice into it.
Which sensor should be the main speed source?
An undriven wheel gives the truest road speed, because it doesn't spin up under power. Use the transmission sensor if it's all you have.
Is there a Nexus version of this?
Yes, the Nexus setup is covered in our Nexus vehicle speed article. Need help choosing sensors for your build? Contact us.
