Hello Angela,
Always difficult to diagnose without examination, but this could be as simple as a dirty contact on a sensor on one of the wheels. Or possibly corrosion on one of the signal toothed rings etc. Someone more experienced than me with the capabilities of diagnostics, will confirm or otherwise that it would be possible to identify which wheel set up to investigate first.
If it were mine, I would be booking it in to a trusted local garage who can identify the problem for you.
Kind regards,
Gareth.