A very common symptom we are presented with quite often is a report of ABS or ESP fault, Handbrake fault, maybe depollution fault and sometimes engine loses power or goes into 'limp mode'.
The fault may go away if you stop and restart the engine. The fault can be due to an EGR valve sticking. The engine computer tells the ABS computer that it's information is not valid and the handbrake computer needs information from the ABS so it also reports a fault because it is a secondary brake and may have safety implications. When you restart the engine, the EGR valve goes through a cleaning routine and frees off for a while.
Diagnosis is reasonably easy and it's a case of replacing the EGR valve.