line lock??

Did you press the brakes?

 

Yup, or while locking the line lock. I suggest just locking the line lock and then using the brakes at the same time as throttle.

 

Enable the line lock, press the brake and hold it, then mash the throttle in a 2WD car and you should see either the car stalling or do a burnout.
--- Post updated ---
You can also just enable it and then try braking, then only 2 wheels should lock up.

 

There's a misunderstanding about what a line lock is.

Line lock is a mechanism to lock the pressure on the chosen brake line.

If you choose to lock the pressure on the front line, it means the pressure of the front brakes will be locked (freezed) at their current pressure. If you were not pressing the brake pedal, then it will get locked at zero pressure. If you were half-pressing the brake pedal, it will lock at 50% pressure. Etc.

Now, how you use the line locking mechanism, is up to the driver. You may choose to lock the rear brakes at 0% pressure, and use the pedal to therefore modulate only the front wheels. This is a typical way to use line locks.

Another way could be to lock the fronts at 100% pressure, and then never touch the brake pedal (which would act on only the rear brake line). This provides less control over the car behaviour during burnout, but for a very simple burnout it can work too.

 

Pick the rear wheel line lock, enable it, press the brakes and hold them, press the throttle while holding brakes and you should do a burnout.
If you have any more trouble, use the "pedals app" and record the video of what are you doing.