2004 S60. First they reprogrammed the PCM after CEL came on. Next day came on again and I took it back to mechanic, they ran diagnostics again and determined timing belt problem. After replacing timing belt, solenoid and both actuators I picked up the car. Total repairs $3500 at this point. 2 days later check engine light is back on again. My question is shouldn't all the issues be showing up on the scanner the first time? How can there be a new code again, it's only been a couple days...

 

What codes have appeared each time?

 

codes just mean a device is reporting an unexpected signal to the ECU. Some codes will set immediately (say you unplugged a sensor... the ECU will read the open circuit right away) other codes are "averaging" meaning they take a sample of readings over time or after some run time data / criteria has been met. Fuel trim errors are typically in the averaging category since there's different mechanisms for managing fuel mix at idle vs at speed. Who did the work - a dealer or an indy shop? It would be useful to go back to the original diagnosis and see what codes originally presented then what codes are now being presented after the repairs to see if they are related (or if the initial diagnosis was wrong).