What would cause the ABS and TCS system to stop functioning?

I recently had my timing chain replaced. When I picked up my car from the mechanic I noticed that both the ABS and TCS lights were on (they were not on before). I have since realized (after trying to drive in the snow) that both of these systems are not functioning. What could my mechanic have done when he replaced the timing chain that would have caused these systems to stop functioning? Thank you.