How ECU traction control works
When a driven tire breaks loose, it spins faster than the car is traveling. The difference between the two is wheel slip. With wheel speed sensors on both driven and undriven wheels, the ECU can measure that slip continuously. Some slip is good, since a tire makes its best grip with a small amount of it. Too much and you're just making smoke.
Haltech's traction control compares measured slip against the amount you've said you want, and when there's too much, it cuts cylinders to pull power until the tires hook back up. Then it brings power back in at the rate you choose.
Choosing a traction control type
| Type | How it decides how much to cut | What you need |
|---|---|---|
| PID From Vehicle Speeds | A closed loop controller works out the cut needed to hold slip at your target | At least one front and one rear wheel speed sensor |
| Percentage Cut | When slip goes past the Desired Slip table, power is cut by the amount in the Cut Percentage table | Wheel speed inputs, and time to map both tables |
| Vehicle CAN Torque Limit | Uses a torque limit sent over CAN by a supported factory module | A vehicle with a compatible CAN unit that broadcasts a torque limit |
Percentage Cut is predictable: you decide exactly how hard the ECU reacts to each amount of excess slip. PID mode is more adaptive, because the controller keeps adjusting until slip matches the target, but it has to be tuned. The PID Tuning page sets how quickly and aggressively that closed loop control responds. If PID control is new to you, read our PID explainer first.
Core settings
| Setting | What it does | Our advice |
|---|---|---|
| Switch Enable | Lets a switch turn traction control on and off | Worth having on any car that sees both street and track |
| Input - Mode | Digital - Switched uses a physical switch on an AVI or SPI. Vehicle CAN uses a CAN device such as a keypad | A Haltech CAN keypad saves wiring if you already have one |
| Driven Wheel Minimum Speed | Traction control stays off until the wheels are faster than this | Needed because slip can't be calculated reliably at very low speed. Keep it low enough that launches are still covered if that's what you want |
| Ramp Out Rate | How quickly power returns after a cut | Start gentle. Too fast and the tires break loose again straight away |
| Cut Method | Ignition cut or injection cut | Ignition cut is the more common choice, and it usually responds fastest |
Cutting spark removes power on the very next firing event. Cutting fuel takes a little longer to show up, because fuel already in the port or cylinder still burns. Injection cut can make sense on some setups, for example where unburned fuel in a hot exhaust is a concern, but ignition cut is where we start.
Conditional activation
Sometimes you only want traction control active under certain conditions: above a certain speed, in a particular gear, or only when a switch is on and the car is rolling. That's what the Conditional Activation page does.
- Condition Enable: adds an ECU condition that must be met before traction control can work.
- When Traction Control Switch is On plus And/Or: combines the switch with the condition. Choose And to require both, or Or for either.
- Select: the ECU channel to test, such as vehicle speed or gear.
- Maths: the comparison to make. All the usual operators are there: =, ≠, >, <, ≥ and ≤.
- Value: the number the channel is compared against.
For example, you might set traction control to run only when the switch is on and gear is greater than or equal to 2, leaving first gear to your launch strategy.
Our first-setup approach
- Get the wheel speed sensors right first. Drive in a straight line and confirm the driven and undriven wheels read the same speed. If they don't agree when nothing is slipping, traction control will cut when it shouldn't. See traction control wiring.
- Start with a generous slip target so the system only steps in when things are clearly out of hand.
- Log slip, cut and wheel speeds together, and tighten the target in small steps.
- Adjust ramp out until power comes back smoothly without re-lighting the tires.
Troubleshooting
| Symptom | Usually |
|---|---|
| Cuts power when the car isn't slipping | Wheel speed sensors disagree. Check calibration, tire size settings and wiring |
| Never activates | Below Driven Wheel Minimum Speed, switch off, or a conditional activation rule not met |
| Car bucks or surges on corner exit | Ramp Out Rate too fast, or the slip target too tight |
| Still spins the tires with it on | Slip target too generous, or cut percentage too small |
FAQ
Do I need four wheel speed sensors?
For PID From Vehicle Speeds, the minimum is one front and one rear sensor. More sensors give the ECU a better picture of what each wheel is doing.
Is traction control the same as torque management?
No. Traction control reacts to measured wheel slip. Torque management is a separate feature with its own setup. See Haltech's advanced torque management for that side of things.
